BTW I have calculated the cost of these Electrolytics from Maplin=£29 (p&p free over £10) and from Cricklewood=£4.18 (inc.VAT) + p&p How can there be such a variance!! There were certain values unavailable= 0.47mF & 0.33mF
Since I have already ordered, this is purely academic.
_________________
Michael
Well, I did give you some advice on buying electrolytics, knowing what rip-offs many retail organizations are. This is not unique to the UK but there is the question of what grades you actually ordered, as prices vary considerably between cheapest of all types and boutique brand "audio grade" electrolytics. You were looking for low ESR or, if large power supply electros, they may be referred to as "high ripple current" types but this will not likely be an issue in a tape recorder. I gave you an example of Panasonic FC type which is widely available.
Like anything targeted at audio or hobbyists fanatics, these components can be unimaginably expensive, simply to satisfy buyer expectations and soak up the amount of spare cash in some wallets, regardless of any real merit.
As AndrewT mentioned, Styrol, as well as Styroseal, Styroflex, Styrolam and no doubt many more Styro... trade names refer to various polystyrene film capacitors once supplied by many manufacturers. The main issue with them is that being polystyrene, they are very easily damaged by prolonged heating of the leads or contact with the iron. Otherwise, leave them alone and they can last a lifetime and again, you don't need to replace them.
Thanks for the advice, Ian. The only 'rip-off' in this transaction (I hope!) is the cost of Fed-Ex. I ordered from Mouser and tried to get Panasonic where available, otherwise, as there's no indication on the Parts List other than 'values' it's 'Hobson's Choice' so I ordered 'same voltage or higher' but same values (of course). I now wait for Fed-Ex to deliver.
____________________
Michael
So you think FedEx is is a rip-off? Well, I have to pay them $US39 for anything from a empty packet upwards to $200 worth of goods, so spare me the tears - I have plenty myself 
.
Japanese service parts lists usually omitted their component references because foreign agents only stocked locally available types and usually serviced many other brands too. There were, even in the 1980s, few other electrolytic types to choose from, apart from specific duty types, listed as such.
More recently, the explosion in switched mode (SMPS) power supplies has introduced many and better performing caps which generally, are better for audio applications too, so we use them at every opportunity, specifying them as replacements and ignoring the basic grades.
There is a downside in that there are now many players in the market with a confusion of brands and grades out there so it becomes necessary (as a repairer at least) to settle on a widely acceptable, reliable grade for general audio use. What is used on new projects or high-end gear is a matter of one's understanding, fancy and pocket depth but that isn't the issue here.
. Japanese service parts lists usually omitted their component references because foreign agents only stocked locally available types and usually serviced many other brands too. There were, even in the 1980s, few other electrolytic types to choose from, apart from specific duty types, listed as such.
More recently, the explosion in switched mode (SMPS) power supplies has introduced many and better performing caps which generally, are better for audio applications too, so we use them at every opportunity, specifying them as replacements and ignoring the basic grades.
There is a downside in that there are now many players in the market with a confusion of brands and grades out there so it becomes necessary (as a repairer at least) to settle on a widely acceptable, reliable grade for general audio use. What is used on new projects or high-end gear is a matter of one's understanding, fancy and pocket depth but that isn't the issue here.
New electrolytic capacitors now in Pre/Amp PCB.
First - test supply voltage: 239v AC from UPS.
Voltages at Fuse Panel:
Chassis Gnd - BLK Xfmr Should read 95v. Does read 78v. No fuse reads 75v.
Chassis Gnd - YLW. Xfmr Should read 30v. Does read 13v. No fuse reads 11.6v.
Chassis Gnd - ORG - Xfmr Should read 25v. Does read 15.6v No Fuse reads 26v
Chassis Gnd - GRY - Xfmr Should read 9.5v. Does read 4.4v. No Fuse reads 7.6v.
Quite bizarre. None of the readings tally with the AKAI requirements. I'm assuming here that all AC voltages are relative to Chassis GND.
_____________________
Michael
First - test supply voltage: 239v AC from UPS.
Voltages at Fuse Panel:
Chassis Gnd - BLK Xfmr Should read 95v. Does read 78v. No fuse reads 75v.
Chassis Gnd - YLW. Xfmr Should read 30v. Does read 13v. No fuse reads 11.6v.
Chassis Gnd - ORG - Xfmr Should read 25v. Does read 15.6v No Fuse reads 26v
Chassis Gnd - GRY - Xfmr Should read 9.5v. Does read 4.4v. No Fuse reads 7.6v.
Quite bizarre. None of the readings tally with the AKAI requirements. I'm assuming here that all AC voltages are relative to Chassis GND.
_____________________
Michael
I should have identified the equipment I am testing - it is an AKAI GX-635D 10 1/2" R - R NAB tape recorder.
_______________
Michael
I guess you just want to verify what you see on the schematic. However, those separate transformer winding voltages you quote are measured directly across each winding's terminals, leads etc. Otherwise, depending on whether a rectifier is involved or whether the circuit even has a ground connection, the AC multimeter readings WRT ground will certainly seem bizarre.
All you need to read (if at all) is to confirm that the DC output of the power supplies is within 5% or so of the marked voltages and you check this particularly on the preamp boards. Measure this WRT power supply ground (pin 21), which may not be chassis ground - it could be a separate wire. Look at the layout diagram for the particular PCB's connections to find it, if fitted. Since you were replacing mostly signal capacitors, I think the matter of audio getting through correctly is more the concern. Use the recorder and check this aspect if your 21V power supply is correct.
For caps in the power supply and bypassing the power rail, this only confirms that they are not about to explode because of wrong rating or orientation. I think by now though, you would already have realised that, the hard way.
All you need to read (if at all) is to confirm that the DC output of the power supplies is within 5% or so of the marked voltages and you check this particularly on the preamp boards. Measure this WRT power supply ground (pin 21), which may not be chassis ground - it could be a separate wire. Look at the layout diagram for the particular PCB's connections to find it, if fitted. Since you were replacing mostly signal capacitors, I think the matter of audio getting through correctly is more the concern. Use the recorder and check this aspect if your 21V power supply is correct.
For caps in the power supply and bypassing the power rail, this only confirms that they are not about to explode because of wrong rating or orientation. I think by now though, you would already have realised that, the hard way.
Thank you Ian for this. I think I shall leave the Power Cct. for this moment while satisfying the reason for bringing it into discussion. The diversion into questioning the power supply was caused by a queer reading at the Collector of one of the KSC1845 - by queer I mean no reading at all. In order to be more specific I shall make a table of all the transistor voltage readings for all the new Pre/Amp transistors and post it here. I am hopeful of not disturbing the Power PCB.
________________
Michael
________________
Michael
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OK, you don't say which transistor but since the collectors are all coupled either directly or via a single resistor to the 21V rail, it shouldn't take more a few seconds with the DMM to deduce where the problem lies. You don't need to do a full circuit analysis and report to diagnose local problems like this.
AKAI GX-635D following new Pre/Amp transistors & electrolytic caps:
OK. Now I know what happened - my cheapo meter HP9804 (Hold Peak) packed up and refused to read more than 0.00vDC. I moved on to my Thandar DMM with the following results tabled:
TR1 (L) B=0.34 C=1.33 E=0.05 TR1 (R) B=0.03 C=1.33 E=0.58
TR1 (L) B=1.34 C=9.51 E=0.59 TR2 (R) B=0.60 C=9.37 E=1.22
TR3 (L) B=0.31 C=8.88 E=1.06 TR3 (R) B=1.06 C=8.68 E=1.76
TR4 (L) B=1.81 C=8.64 E=1.07 TR4 (R) B=1.07 C=8.75 E=1.76
TR5 (L) B=8.54 C= /// E=7.67 TR5 (R) B=8.55 C= /// E=7.73 **
TR6 (L) B=3.65 C=15.0 E=2.93 TR6 (R) B=3.67 C=14.9 E=2.93
TR7 (L) B=0.38 C=1.14 E=0.22 TR7 (R) B=0.39 C=1.15 E=0.21
TR8 (L) B=1.16 C=7.59 E=0.42 TR8 (R) B=0.61 C=7.17 E=0.43
TR9 (L) B=0.87 C=1.71 E=0.19 TR9 (R) B=0.87 C=1.69 E=0.17
TR10(L) B=1.73 C=7.03 E=1.25 TR10(R) B=1.70 C=9.66 E=0.93
FET11(L)D= // G=0.16 S= // FET11(R)D=// G=0.47 S= // **
TR12(L) B=11.56 C= // E=10.55 TR12(R) B=11.18 C=// E=10.49
** In TR5(L)&(R)the Collectors initially read high, disappearing instantly
** FET (L)&(R) Drain and Source give a reading disappearing instaqntly.
___________________
Michael
.
If you look at the schematic, TR5 collector is connected to the 21V rail so, if you mean "no reading" by ///, then you have a soldering, lead ID or another meter problem. If you realise it should be 21V, then that's fine.
FET TR11 gate is referenced to OV by a 3.3M resistor so its not surprising even the tiny load of your meter soon flattens any static gate charge as it probably switches state when you attempt to measure DC there.
Working transistors (the ordinary bipolar junction transistor variety) have a Base-Emitter voltage drop of around 0.65V. If you don't measure this voltage difference in circuit, there is an error, either in the power to the circuit, the fitting of replacement parts or your measurements. I'd suggest you need to consider both your meters as suspect, if not for their vintage, at least their batteries.
I guess it's too late to remind you not to change parts in both channels at once as you no longer have a working frame of reference for comparison of right and wrong. There are some basics that can be slowly checked and rechecked though. Patience + a reliable meter may still save the day.
You can easily check the figures from your measurements and some actually appear correct but overall, most show L, R or both transistors with wrong B-E measurements and they seem all over the place, so to check your meter first, just power up and measure across the B-E leads (take care not to short them) and compare with the subtracted B-E differences from your posted results in each case. There is no need to present a tabulation here as you are looking to check the differences for your own understanding - the individual terminal voltages WRT OV, ground etc. are not useful until the measurements are certain. Only errant B-E differences are of interest.
FET TR11 gate is referenced to OV by a 3.3M resistor so its not surprising even the tiny load of your meter soon flattens any static gate charge as it probably switches state when you attempt to measure DC there.
Working transistors (the ordinary bipolar junction transistor variety) have a Base-Emitter voltage drop of around 0.65V. If you don't measure this voltage difference in circuit, there is an error, either in the power to the circuit, the fitting of replacement parts or your measurements. I'd suggest you need to consider both your meters as suspect, if not for their vintage, at least their batteries.
I guess it's too late to remind you not to change parts in both channels at once as you no longer have a working frame of reference for comparison of right and wrong. There are some basics that can be slowly checked and rechecked though. Patience + a reliable meter may still save the day.
You can easily check the figures from your measurements and some actually appear correct but overall, most show L, R or both transistors with wrong B-E measurements and they seem all over the place, so to check your meter first, just power up and measure across the B-E leads (take care not to short them) and compare with the subtracted B-E differences from your posted results in each case. There is no need to present a tabulation here as you are looking to check the differences for your own understanding - the individual terminal voltages WRT OV, ground etc. are not useful until the measurements are certain. Only errant B-E differences are of interest.
Thank you Ian. I shall take your words into my Workshop and test the B-E leads as you suggest. What does "across the B-E leads" mean - and how do I interpret it? You can see I am somewhat out of my depth here - so apologies for lack of insight!
You are right, it is indeed too late, for all the transistors and electrolytics are replaced. Bull in a china shop is nothing on my approach I fear! But I shall take my soldering iron over all the new joints and re-melt them as a form of insurance!
I am somewhat worried about two of the Styrol capacitors - Nos. C29 and C30. They had been physically glued down to the PCB. Why? I don't know - but I carefully separated them from the PCB and stood them up like the other Styrol Caps. May I have damaged them? Hard to say - but if so would this be the cause of my problem?
Meters. I only have one now - the Thandar TM361. The Battery in the Thandar was originally 6 x 1.5 'C' cells. I changed that to 2 x PP3 9v wired in parallel in order to prolong battery life and not land up with leaking 'C' cells inside the meter - which was why I did this. Do you think I should revert to the 6 x 'C' format? I am not sure whether the internal resistance of the two 9v. is the same as 6 x 'C' cells - or even if such a change has any bearing here.
_______________
Michael
Ha-ha! You clicked on or hovered over the U character above the message window. I'm sure you're aware it means to underline or underscore the selected text, as I have just done. 
Polystyrene caps were known to be microphonic (sensitive to sound or vibration) and many film caps and other types were glued down in an effort to damp this in sensitive applications like mic, tape head and phono preamps. FM radio tuners and some TV tuners were once also full of wax and bits of sponge to do the same thing there. So yep, a bull in a china shop! Place them back where they belong and use blue-tack or silicone RTV, building mastic or similar removable adhesive. You may have damaged the caps if you have peeled off the outer film layers and disturbed the aluminium foil beneath. If there is no short between the terminals (yes, across the leads!) they be OK if closed up and sealed over as you fasten it to the PCB again. Otherwise, you'll need to replace them but now you would use a multilayer ceramic COG type cap, 50V rated, because those wonderful old polystyrene caps are too rare and expensive to contemplate if they are any size above a few thousand pF.
If you have a why? issue with something, just ask first. If I don't know, others here will, and have much better explanations too, if it's important. However, assume first that the designer(s) did know what they were doing and there is no justification for removing things we don't understand. After all, you once bought an Akai tape machine but it was out of admiration for brand excellence rather than with a view to to redesigning and rebuilding it, I'm sure.
The six C cells in the Thurlby Thandar meter will be for heavy power consumption. I had a couple of quality LCD DMMs in the 1970s that went 12 months on a single PP3 battery so I don't see why this one needs so much current for an LCD model (is it actually LED?) but that may be why they don't make or sell them now - only thumping great bench models for precision applications. The crazy thing is, you could now buy a cheap but quite adequate DMM for less than the price of those batteries at a hardware bargain store or at any of hundreds of market sellers. Just make sure it goes down to a 2V range so that you can measure those small voltages. Here's some armchair shopper's offerings for a bit more than the £5 you might pay for something similar or maybe even better, on the street. http://www.amazon.co.uk/Digital-Multimeter-Tester-Multi-Meter-MultiTester/dp/B004HSSJXG
"across the B-E leads" means literally that. I had spelt out the B and E symbols as base and emitter already and when we measure across terminals, leads etc. It means to make a measurement between those points, to bridge across, measure over etc. with the probes. e.g. To measure a voltage you place the probes across the source terminals. You could say "place the red probe on the red terminal and the black probe on the black terminal but brevity, common sense and convention rule. I trust I don't need to go further with that.
Polystyrene caps were known to be microphonic (sensitive to sound or vibration) and many film caps and other types were glued down in an effort to damp this in sensitive applications like mic, tape head and phono preamps. FM radio tuners and some TV tuners were once also full of wax and bits of sponge to do the same thing there. So yep, a bull in a china shop! Place them back where they belong and use blue-tack or silicone RTV, building mastic or similar removable adhesive. You may have damaged the caps if you have peeled off the outer film layers and disturbed the aluminium foil beneath. If there is no short between the terminals (yes, across the leads!) they be OK if closed up and sealed over as you fasten it to the PCB again. Otherwise, you'll need to replace them but now you would use a multilayer ceramic COG type cap, 50V rated, because those wonderful old polystyrene caps are too rare and expensive to contemplate if they are any size above a few thousand pF.
If you have a why? issue with something, just ask first. If I don't know, others here will, and have much better explanations too, if it's important. However, assume first that the designer(s) did know what they were doing and there is no justification for removing things we don't understand. After all, you once bought an Akai tape machine but it was out of admiration for brand excellence rather than with a view to to redesigning and rebuilding it, I'm sure.
The six C cells in the Thurlby Thandar meter will be for heavy power consumption. I had a couple of quality LCD DMMs in the 1970s that went 12 months on a single PP3 battery so I don't see why this one needs so much current for an LCD model (is it actually LED?) but that may be why they don't make or sell them now - only thumping great bench models for precision applications. The crazy thing is, you could now buy a cheap but quite adequate DMM for less than the price of those batteries at a hardware bargain store or at any of hundreds of market sellers. Just make sure it goes down to a 2V range so that you can measure those small voltages. Here's some armchair shopper's offerings for a bit more than the £5 you might pay for something similar or maybe even better, on the street. http://www.amazon.co.uk/Digital-Multimeter-Tester-Multi-Meter-MultiTester/dp/B004HSSJXG
"across the B-E leads" means literally that. I had spelt out the B and E symbols as base and emitter already and when we measure across terminals, leads etc. It means to make a measurement between those points, to bridge across, measure over etc. with the probes. e.g. To measure a voltage you place the probes across the source terminals. You could say "place the red probe on the red terminal and the black probe on the black terminal but brevity, common sense and convention rule. I trust I don't need to go further with that.
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Ha-ha! You clicked on or hovered over the U character above the message window. I'm sure you're aware it means to underline or underscore the selected text, as I have just done.
Polystyrene caps were known to be microphonic (sensitive to sound or vibration) and many film caps and other types were glued down in an effort to damp this in sensitive applications like mic, tape head and phono preamps. FM radio tuners and some TV tuners were once also full of wax and bits of sponge to do the same thing there. So yep, a bull in a china shop! Place them back where they belong and use blue-tack or silicone RTV, building mastic or similar removable adhesive. You may have damaged the caps if you have peeled off the outer film layers and disturbed the aluminium foil beneath. If there is no short between the terminals (yes, across the leads!) they be OK if closed up and sealed over as you fasten it to the PCB again. Otherwise, you'll need to replace them but now you would use a multilayer ceramic COG type cap, 50V rated, because those wonderful old polystyrene caps are too rare and expensive to contemplate if they are any size above a few thousand pF.
If you have a why? issue with something, just ask first. If I don't know, others here will, and have much better explanations too, if it's important. However, assume first that the designer(s) did know what they were doing and there is no justification for removing things we don't understand. After all, you once bought an Akai tape machine but it was out of admiration for brand excellence rather than with a view to to redesigning and rebuilding it, I'm sure.
The six C cells in the Thurlby Thandar meter will be for heavy power consumption. I had a couple of quality LCD DMMs in the 1970s that went 12 months on a single PP3 battery so I don't see why this one needs so much current for an LCD model (is it actually LED?) but that may be why they don't make or sell them now - only thumping great bench models for precision applications. The crazy thing is, you could now buy a cheap but quite adequate DMM for less than the price of those batteries at a hardware bargain store or at any of hundreds of market sellers. Just make sure it goes down to a 2V range so that you can measure those small voltages. Here's some armchair shopper's offerings for a bit more than the £5 you might pay for something similar or maybe even better, on the street. http://www.amazon.co.uk/Digital-Multimeter-Tester-Multi-Meter-MultiTester/dp/B004HSSJXG
"across the B-E leads" means literally that. I had spelt out the B and E symbols as base and emitter already and when we measure across terminals, leads etc. It means to make a measurement between those points, to bridge across, measure over etc. with the probes. e.g. To measure a voltage you place the probes across the source terminals. You could say "place the red probe on the red terminal and the black probe on the black terminal but brevity, common sense and convention rule. I trust I don't need to go further with that.
Many thanks indeed, Ian, for your interpretations and your patience! Here are my findings:
1.The Thandar is, I think, an LCD model. I'm not sure how to recognize LCD from LED screen. It will not read the Collector voltage at the collector of TR12. So:
2. I have just taken delivery of a replacement meter: UNIT-T UT61E which, unhelpfully, came with an Operating Manual totally in Chinese hieroglyphics. I have emailed the seller about this. BUT it does read the collector at TR12.
3. Both C6's had defective solder joints - which accounted for the lack of collector voltage at TR5. Once the iron was applied all was changed. Thank you for pointing out this possible problem area, Ian.
4. Using the new UT61E I have re-tabulated the B-C-E readings of all TR's and have a marked difference from the readings I published.
5. I have tabulated the B-E readings of TR's 1 - 12 with the result: all pairs (TR1 and TR1b &c) show Very Close readings to each other and the over-all measurements are between 0.55v and 0.63v - but mostly around 0.60v.
I think now that for good measure, and before putting the machine back together, I shall take readings of TR13 - 23. These have not been subjected to much of my blundering china-shop activities except the Caps. I shall also carefully re-fix the two Styrol caps as they were - to the PCB. My activities there did reveal the outer layer of foil on one cap - but I don't think I damaged them. Checking for a short on their leads, with the power switched off, shows no reading.
6. I have tabulated the B-C-E readings of TR13 - TR23 and find them about right. TR21 &22 are the Timing Cct. but I can't figure out the purpose of TR20 & 23. TR15 & 16 have a B-E of 0.36v and TR14 only has: B=0 C=0.70 E=0.0 - but this is in the Freq.Response Cct. for the two speeds of transport.
7. Looking at the Cct Diag the peripheral line shows many encircled numbers - which may mean test points? What I can't fathom is what these points physically look like, where they are or how to recognize them. I am looking to find, for example, Test Point/Contact pin (43) shewn in the bottom (L) corner of the Cct Diag. There I should measure +22v.
Maybe things are looking up? ( just may be!)
_____________________
Michael
UT61E is the top model in that 61 Range which is an excellent budget meter. It even has adaptors for component measurements and viewing, logging and documenting results on your PC, like its bigger brothers. It should suit you to a "T" (pun intended) - You should have no problems with it, short of usual battery failure from leaving the power on. If you Google "UT61E review", specifications, instructions etc. you will find lots of information. There are also on-line multi-lingual versions of the manual at the the Uni-T website too. Here's one from your own backyard, so don't say we don't look after you: http://www.industrial-needs.com/manual/manual-pce-ut-61e.pdf
You will likely discover a wealth of info. out there from DIYs, professionals and idiots too, A little searching is often very helpful, not only for the facts but the wrinkles, hidden truth and how to get the most for your money.
LED displays are what you saw from the 1960s - luminescent, usually red, fixed size, numeric only characters and thirsty for current. They are still used for indicator lights and displays that must be viewed from a distance or in poor lighting conditions without a backlight. Of course, the world is in a massive move to LED lighting presently, which I'm sure you are aware of, if not engaged in.
LCD dispays are photo-restrictive and appear as black characters on a light, reflective background. This is what you've be staring at for the past 35 years on most digital displays like your UT61 and probably the others too. Your TV and PC also use LCD technology to filter and modulate the backlighting of their screens such that you see high contrast, luminous images.
As you progress into the Akai's muting and timing circuits, you find they are powered only periodically or when in one mode or another according to the switching and relays controlled by digital and manual control circuits. Don't be disappointed if you never get to fathom out how everything works or where the power control comes from. You are called "technician" or expert then and get to wear Lego-Man workclothes. I certainly don't propose to go through it part by part because it takes a lot more time to investigate and analyse it, even though the general principles and circuitry will be fairly obvious to experienced techs.
I'm not sure whether you are on a voyage of discovery here of just looking to confirm all the numbers because you can. What may make it awkward, is that when the machine is operated, some parts such as timer switch TR22 will only become powered and carry out their function in certain operating modes. Otherwise they may be unpowered. Don't be surprised that the machine has to be put through all its paces to find out whether voltages are present and correct - something you can otherwise tell more usefully by simply checking that it works satisfactorily in all modes.
I wouldn't expect DC voltages to be wrong or be much use in tracking down sick caps. which is all you have to look for and why I insist on blanket replacement - though only a stage at a time, please! Briefly, TR20,23 switch and latch the 22V rail power to the 21.2V rail of the mute, tape sense and speed change board. i.e they power it as required. Be aware that some caps are the timing element in a delayed switch or timer circuit so try to keep all replacement cap. values correct in those circuits if you don't know which is the specific timing element.
The numbers at the broken lines of the schematic refer to the corresponding numbered wire connections to other parts of the circuit, to other boards, devices etc. outside the broken line. If you look at the PCB assembly images, those numbers appear wherever the corresponding lead is physically inserted or connected.
I'm skeptical of an opened-up film capacitor - It could be fine for years to come but still compromised. I would put replacements on your list of things to do when there's nothing to do. Have fun
You will likely discover a wealth of info. out there from DIYs, professionals and idiots too, A little searching is often very helpful, not only for the facts but the wrinkles, hidden truth and how to get the most for your money.
LED displays are what you saw from the 1960s - luminescent, usually red, fixed size, numeric only characters and thirsty for current. They are still used for indicator lights and displays that must be viewed from a distance or in poor lighting conditions without a backlight. Of course, the world is in a massive move to LED lighting presently, which I'm sure you are aware of, if not engaged in.
LCD dispays are photo-restrictive and appear as black characters on a light, reflective background. This is what you've be staring at for the past 35 years on most digital displays like your UT61 and probably the others too. Your TV and PC also use LCD technology to filter and modulate the backlighting of their screens such that you see high contrast, luminous images.
As you progress into the Akai's muting and timing circuits, you find they are powered only periodically or when in one mode or another according to the switching and relays controlled by digital and manual control circuits. Don't be disappointed if you never get to fathom out how everything works or where the power control comes from. You are called "technician" or expert then and get to wear Lego-Man workclothes. I certainly don't propose to go through it part by part because it takes a lot more time to investigate and analyse it, even though the general principles and circuitry will be fairly obvious to experienced techs.
I'm not sure whether you are on a voyage of discovery here of just looking to confirm all the numbers because you can. What may make it awkward, is that when the machine is operated, some parts such as timer switch TR22 will only become powered and carry out their function in certain operating modes. Otherwise they may be unpowered. Don't be surprised that the machine has to be put through all its paces to find out whether voltages are present and correct - something you can otherwise tell more usefully by simply checking that it works satisfactorily in all modes.
I wouldn't expect DC voltages to be wrong or be much use in tracking down sick caps. which is all you have to look for and why I insist on blanket replacement - though only a stage at a time, please! Briefly, TR20,23 switch and latch the 22V rail power to the 21.2V rail of the mute, tape sense and speed change board. i.e they power it as required. Be aware that some caps are the timing element in a delayed switch or timer circuit so try to keep all replacement cap. values correct in those circuits if you don't know which is the specific timing element.
The numbers at the broken lines of the schematic refer to the corresponding numbered wire connections to other parts of the circuit, to other boards, devices etc. outside the broken line. If you look at the PCB assembly images, those numbers appear wherever the corresponding lead is physically inserted or connected.
I'm skeptical of an opened-up film capacitor - It could be fine for years to come but still compromised. I would put replacements on your list of things to do when there's nothing to do. Have fun
UT61E is the top model in that 61 Range which is an excellent budget meter. It even has adaptors for component measurements and viewing, logging and documenting results on your PC, like its bigger brothers. It should suit you to a "T" (pun intended) - You should have no problems with it, short of usual battery failure from leaving the power on. If you Google "UT61E review", specifications, instructions etc. you will find lots of information. There are also on-line multi-lingual versions of the manual at the the Uni-T website too. Here's one from your own backyard, so don't say we don't look after you: http://www.industrial-needs.com/manual/manual-pce-ut-61e.pdf
You will likely discover a wealth of info. out there from DIYs, professionals and idiots too, A little searching is often very helpful, not only for the facts but the wrinkles, hidden truth and how to get the most for your money.
LED displays are what you saw from the 1960s - luminescent, usually red, fixed size, numeric only characters and thirsty for current. They are still used for indicator lights and displays that must be viewed from a distance or in poor lighting conditions without a backlight. Of course, the world is in a massive move to LED lighting presently, which I'm sure you are aware of, if not engaged in.
LCD dispays are photo-restrictive and appear as black characters on a light, reflective background. This is what you've be staring at for the past 35 years on most digital displays like your UT61 and probably the others too. Your TV and PC also use LCD technology to filter and modulate the backlighting of their screens such that you see high contrast, luminous images.
As you progress into the Akai's muting and timing circuits, you find they are powered only periodically or when in one mode or another according to the switching and relays controlled by digital and manual control circuits. Don't be disappointed if you never get to fathom out how everything works or where the power control comes from. You are called "technician" or expert then and get to wear Lego-Man workclothes. I certainly don't propose to go through it part by part because it takes a lot more time to investigate and analyse it, even though the general principles and circuitry will be fairly obvious to experienced techs.
I'm not sure whether you are on a voyage of discovery here of just looking to confirm all the numbers because you can. What may make it awkward, is that when the machine is operated, some parts such as timer switch TR22 will only become powered and carry out their function in certain operating modes. Otherwise they may be unpowered. Don't be surprised that the machine has to be put through all its paces to find out whether voltages are present and correct - something you can otherwise tell more usefully by simply checking that it works satisfactorily in all modes.
I wouldn't expect DC voltages to be wrong or be much use in tracking down sick caps. which is all you have to look for and why I insist on blanket replacement - though only a stage at a time, please! Briefly, TR20,23 switch and latch the 22V rail power to the 21.2V rail of the mute, tape sense and speed change board. i.e they power it as required. Be aware that some caps are the timing element in a delayed switch or timer circuit so try to keep all replacement cap. values correct in those circuits if you don't know which is the specific timing element.
The numbers at the broken lines of the schematic refer to the corresponding numbered wire connections to other parts of the circuit, to other boards, devices etc. outside the broken line. If you look at the PCB assembly images, those numbers appear wherever the corresponding lead is physically inserted or connected.
I'm skeptical of an opened-up film capacitor - It could be fine for years to come but still compromised. I would put replacements on your list of things to do when there's nothing to do. Have fun
Thanks Ian. I am very appreciative of all the help you have been giving - without it I am sure the AKAI would have been a write-off - a large door stop.
The Thandar IS an LED for it follows your description precisely. It is not as sensitive as the UT61E though.
I have been checking all the voltages again and there is no change - that is, nothing has wandered and so the time has come to re-assemble for a test.
I have tried - though unsuccessfully - to inject a tone at various points in the pre/amp PCB but I think the only real test is going to be playing a tape and testing a couple of mics and Line level devices once the machine is back together.
Thanks for your approval of my new meter. I had already been on-line and found a useful photographic documentary of the attributes. The RS232 may possibly be useful but I have no RS232 socket in any of my PC's so I shall either get an RS232 card or an adapter from RS232/USB - if only for the fun of seeing it working that way.
As for my 'voyage of discovery' - it is partly that and to widen my knowledge of the equipment I own. For instance I have just successfully re-foamed my two RE20's - which was a great relief.
Back to the AKAI: I concluded that since the voltages around TR9 remained consistently low - and the voltages around TR14 , TR21 and TR22 were to do with speed-specific changes, then all was probably normal. As you point out they are powered only on demand.
I do a fair amount of live recording and have mostly ElectroVoice microphones + some high end Studio mics like the Calrec Soundfield SPS422 and Boundary Mics by Schoeps. Mostly these are mics I used with Uher 4200 Report and the AKAI + a Studer Revox A-77. Now, of course, I am going 'solid state' with a ZOOM R-300 and LynxStudio cards. Tomorrow my 17yr old son is playing Bruch Viola Fantasie in a public performance - so I shall be recording it. I have many 10.5" reels of Opera which I recorded live in the Brighton area in the 1980's. That was when the AKAI and A-77 machines really rose above my Uhers. But DAT took over from them and only recently have I gone wholly digital.
When I finally re-assemble the AKAI I will post my results. Thanks again - and:
Fingers crossed!
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Michael
Fingers X'd indeed - and it works! The AKAI GX-635D is once again in its rack above the Revox 77-A and playing very well. So now I must thank all those who contributed to it successful return - Especially to Ian Finch without whose timely and patient help and guidance this would not be the success it undoubtedly is. I worked at it like a "Bull in a china shop" did all the wrong things but with Ian's unstinting and undaunted help still got the right result. I even got those pesky MIC and LINE gain-pot knobs back together again. (they're quite something and very difficult to reassemble) Now all I have to do is do some recording with it again . . .
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Michael
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Michael
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