I recently found a Nakamichi BX-100 that someone had chucked out on the street.
Cosmetically, it is in very good condition. Looking inside the cassette tray the heads seem to be in good condition too and the rubber wheels don't look that worn. When I plug it in and turn it on though not much happens the 2 lowest leds of the level lights come on but none of the play/stop/rew buttons work.
I checked the power supply at the transformer with my DMM and it has around 18v on each rail (AC).
I would dearly like to fix this as I have a HUGE box of tapes that have been sitting on a top shelf for about 7 years and I'm quite keen to be reunited with some of their contents 🙂
Also, I recently brought my first oscilloscope so this will be good fodder for it. Iv'e never used one before though and apart from watching a few tutorials on youtube don't really know what I'm doing with it yet.
I guess a good place to start would be to try and get a service manual?
If there is any tape deck experts out there that could give me some advice on how to proceed I would much appreciate it.
Cosmetically, it is in very good condition. Looking inside the cassette tray the heads seem to be in good condition too and the rubber wheels don't look that worn. When I plug it in and turn it on though not much happens the 2 lowest leds of the level lights come on but none of the play/stop/rew buttons work.
I checked the power supply at the transformer with my DMM and it has around 18v on each rail (AC).
I would dearly like to fix this as I have a HUGE box of tapes that have been sitting on a top shelf for about 7 years and I'm quite keen to be reunited with some of their contents 🙂
Also, I recently brought my first oscilloscope so this will be good fodder for it. Iv'e never used one before though and apart from watching a few tutorials on youtube don't really know what I'm doing with it yet.
I guess a good place to start would be to try and get a service manual?
If there is any tape deck experts out there that could give me some advice on how to proceed I would much appreciate it.
First step is to find the service manual and schematics online.
Depending on your level of patience and ability to do diagnostics you may or may not be able to fix it. Lack of experience may be a big handicap here, provided you can solder, think logically and actually understand the schematics you may have a chance. Hopefully exotic spare parts are not required.
Given that it is generally dead from description the first area I would check would be all of the power supplies.
Depending on your level of patience and ability to do diagnostics you may or may not be able to fix it. Lack of experience may be a big handicap here, provided you can solder, think logically and actually understand the schematics you may have a chance. Hopefully exotic spare parts are not required.
Given that it is generally dead from description the first area I would check would be all of the power supplies.
Hi Kevinkr,
Thanks for your reply.
My level of expertise with soldering and making up kits is good and I know the basics on how to check power supplies, passive components etc. Thats about it though.
Today I stripped the panels away from the BX100 PCBs and have started probing it with my scope 😉 The power supply is +/-8v and the caps and rectifier bridge seem to be working fine.
I pulled out the main switch panel and depressing the switches with the probe attached seems to do something as the volts change. I'm wondering if the problem could be in the microprocessor that seems to control everything. as the fault doesn't seem to be confined to one circuit but to everything. I can't get any of the switches to have any affect at all. None of the motors have started to spin yet.
Yes, I should go and do some more internet searching see if i can find a schematic. My preliminary searching has only come up with a user manual.
col.
Thanks for your reply.
My level of expertise with soldering and making up kits is good and I know the basics on how to check power supplies, passive components etc. Thats about it though.
Today I stripped the panels away from the BX100 PCBs and have started probing it with my scope 😉 The power supply is +/-8v and the caps and rectifier bridge seem to be working fine.
I pulled out the main switch panel and depressing the switches with the probe attached seems to do something as the volts change. I'm wondering if the problem could be in the microprocessor that seems to control everything. as the fault doesn't seem to be confined to one circuit but to everything. I can't get any of the switches to have any affect at all. None of the motors have started to spin yet.
Yes, I should go and do some more internet searching see if i can find a schematic. My preliminary searching has only come up with a user manual.
col.
Hi,
You need a circuit for sure. As to the processor being duff, this is the last thing to go for. 99% of faults on consumer gear are usually something simple like a fuse, circuit protector or safety resistor open circuit.
Even when you are convinced the processor is the problem a check on ALL the pins will usually reveal the fault as some input as not being correct.
Edit, Try and trace all the rails, look for large caps that might be rail decoupling and see if they have sensible voltages across them. Look for low value "safety" resistors in the PSU that may be open circuit.
5 volts for the logic seems resonable etc.
You need a circuit for sure. As to the processor being duff, this is the last thing to go for. 99% of faults on consumer gear are usually something simple like a fuse, circuit protector or safety resistor open circuit.
Even when you are convinced the processor is the problem a check on ALL the pins will usually reveal the fault as some input as not being correct.
Edit, Try and trace all the rails, look for large caps that might be rail decoupling and see if they have sensible voltages across them. Look for low value "safety" resistors in the PSU that may be open circuit.
5 volts for the logic seems resonable etc.
Mooly said:
Generally agree here, only exception would be in the instance of a nearby lightening strike, because of the small die geometry in modern digital ICs their tolerance to transient events makes them vulnerable to relatively low voltages. In a previous job I did some lightening strike surge testing on a consumer audio product I helped to design, and despite independent voltage regulators and careful ground plane design the micro-controller (and only the micro-controller) died repeatedly when subjected to a distant simulated lightening strike to ac mains. (~6KV spike for some hundreds of nS) The fix required some minor design changes mostly to the ac input filtering. (Once it's in, its in.. 😀 )
I'd say the first thing to check for is presence of proper supply voltage at the uP (older products probably 5V) and next the check the clock. As Mooly says take a look at the issues he raises.
I think the capstan motor should start as soon as player is turned on. There may be a door-switch or "casette in tray" detector that "kills" all commands.
Arne K
Arne K
Still have not been able to find a service manual. Digging around on the net just seems to come up with commercial sites trying to sell manuals for mega-bux. Hard to believe someone hasn't loaded all the service manuals into a free website making money off the adverts, gawd knows there would be enough audio nerds visiting to make a fortune. Anyway, if anyone out there has a service manual I can stick the pdf on my website for free 🙂
Iv'e been randomly probing resistors and diodes to see if I can find a dead one. Some of them seem to have been purposely soldered to the main board with the legs showing, maybe to dissipate heat? There is one big resistor next to the crystal which strikes me as odd, it seems to be 0 ohms. With my DMM/scope if something is wrong with a component it usually shows O.L (for overload) but that one comes up with 0 ohms. I checked it several times always the same.
I looked at the door switch and that seems to be fine. The one thing that is telling is that as soon as i apply the power the 2 lowest leds on the level meters light up and stay alight.
I also probed all the pins on the microprocessor with power applied and there is definitely stuff flowing through it, so at least it isn't completely dead. Wether the stuff is the right stuff I have no idea.
col.
Iv'e been randomly probing resistors and diodes to see if I can find a dead one. Some of them seem to have been purposely soldered to the main board with the legs showing, maybe to dissipate heat? There is one big resistor next to the crystal which strikes me as odd, it seems to be 0 ohms. With my DMM/scope if something is wrong with a component it usually shows O.L (for overload) but that one comes up with 0 ohms. I checked it several times always the same.
I looked at the door switch and that seems to be fine. The one thing that is telling is that as soon as i apply the power the 2 lowest leds on the level meters light up and stay alight.
I also probed all the pins on the microprocessor with power applied and there is definitely stuff flowing through it, so at least it isn't completely dead. Wether the stuff is the right stuff I have no idea.
col.
BX-100 images
Iv'e put a few photos up, click on "Full Size" for a good view. I will upload some better close up shots later, these are just to give a general idea, it's only 7:30am here at the moment and I haven't had any coffee yet.
http://pix.minirig.org.au/main.php?g2_itemId=408
col.
Iv'e put a few photos up, click on "Full Size" for a good view. I will upload some better close up shots later, these are just to give a general idea, it's only 7:30am here at the moment and I haven't had any coffee yet.
http://pix.minirig.org.au/main.php?g2_itemId=408
col.
Hi There
I have a BX125, so if we assume that model and the '100 behave in a similar way, then here are some observations that might help you. On the 125, in the 'just powered up' state, you do indeed get the bottom 2 LEDs of each level meter illuminated. Also, the 'up' LED of the electronic 'master fader' (which I believe the '100 has too) should be 'on'. The capstan motor only runs during 'playback' and 'record'. The transport has a further 2 motors, one for tape spooling, and another smaller one with a worm-gear on it that drives a cam-system which I think moves the headblock. I have a vague memory of that bit of my unit getting stuck occasionally - you could try giving it a helping hand.
I need to sort the tape-counter out on mine sometime soon so the lid will be off - if I can do some measurements for comparative purposes let me know, however I don't have a 'scope so that might limit things.
BTW, these machines are in a different league to units I've fiddled with by the likes of Technics or Denon, but at the end of the day they are common on a certain on-line auction site, so if you are defeated you should be able to get another for little outlay. I've been in contact with the UK service agent recently, and parts are now difficult to get and are pricey too, so there might be someone near to you who could use the unit for spares, so don't skip it!
Regards
Steve
I have a BX125, so if we assume that model and the '100 behave in a similar way, then here are some observations that might help you. On the 125, in the 'just powered up' state, you do indeed get the bottom 2 LEDs of each level meter illuminated. Also, the 'up' LED of the electronic 'master fader' (which I believe the '100 has too) should be 'on'. The capstan motor only runs during 'playback' and 'record'. The transport has a further 2 motors, one for tape spooling, and another smaller one with a worm-gear on it that drives a cam-system which I think moves the headblock. I have a vague memory of that bit of my unit getting stuck occasionally - you could try giving it a helping hand.
I need to sort the tape-counter out on mine sometime soon so the lid will be off - if I can do some measurements for comparative purposes let me know, however I don't have a 'scope so that might limit things.
BTW, these machines are in a different league to units I've fiddled with by the likes of Technics or Denon, but at the end of the day they are common on a certain on-line auction site, so if you are defeated you should be able to get another for little outlay. I've been in contact with the UK service agent recently, and parts are now difficult to get and are pricey too, so there might be someone near to you who could use the unit for spares, so don't skip it!
Regards
Steve
Hi Steve,
Thanks for that. Yes, if you take the lid off your BX125 maybe you could measure the voltage across the two biggest caps. directly after the rectifier. One is 4700uF 25v (I am getting a reading of 23v there) and the other one is 6800uF 16v (that one is only reading around 1v). You can check them with a standard multimeter. I'm mostly interested in the voltage across the second one.
cheers,
col.
Thanks for that. Yes, if you take the lid off your BX125 maybe you could measure the voltage across the two biggest caps. directly after the rectifier. One is 4700uF 25v (I am getting a reading of 23v there) and the other one is 6800uF 16v (that one is only reading around 1v). You can check them with a standard multimeter. I'm mostly interested in the voltage across the second one.
cheers,
col.
That does sound suspicious. Can you trace it back. I am assuming the negative end goes to ground. Just see where it leads you. The "resistors with the legs showing" They sound like safety resistors. These are designed to go open circuit when overloaded ( without the smoke etc of other types 🙂 ) Have a measure on ohms with it all off. If there is any residual voltage across one it will confuse your DMM. If in doubt unsolder one end to measure. They are normally in the ranges of 1 to 10 ohm. The "thing" near the crystal could be a coil. Also with any microprocessor just measuring on it (particularly around the osc) can spike it and cause it to latch up -- it's no problem but just be aware and keep switching off/on to reset.
Experience says it could be mechanical -- a sticky mech or seized motor that has drawn excessive current and popped something.
Experience says it could be mechanical -- a sticky mech or seized motor that has drawn excessive current and popped something.
Mooly, Thats excellent advice thanks, will follow up on your suggestions. Had a bit of good news / bad news. First the good news.. I found a service manual for a Nakamichi 2 head tape deck!..... the bad news is its not the same model as mine. Its a 480. Which is pretty useless in a technical sense but it is helping with my holistic approach to repair 😀
Hi Col
Got the chance to put the new tape-counter belt in my BX-125, and while I was there I took some measurements for you. The 4700uF has 22.3v on it when the unit is 'stopped', and this drops to 20.6v while 'playing'. The 6800uF measured 11.8v at all times.
I didn't attempt to follow the PCB traces (poor eyesight!), but I guess the 4700 is the un-reg'd dc, and the 6800 is post-regulation. I can tell you for certain that the power-semi device mounted on the metal bracket close by these caps gets mighty hot! Maybe this is a regulator IC or PSU pass-transistor, and the one in your unit has failed, or would that be too simple!!
Regards
Steve
Got the chance to put the new tape-counter belt in my BX-125, and while I was there I took some measurements for you. The 4700uF has 22.3v on it when the unit is 'stopped', and this drops to 20.6v while 'playing'. The 6800uF measured 11.8v at all times.
I didn't attempt to follow the PCB traces (poor eyesight!), but I guess the 4700 is the un-reg'd dc, and the 6800 is post-regulation. I can tell you for certain that the power-semi device mounted on the metal bracket close by these caps gets mighty hot! Maybe this is a regulator IC or PSU pass-transistor, and the one in your unit has failed, or would that be too simple!!
Regards
Steve
thanks for testing that Steve, has put me on the right track. I have done a diode test on that regulator attached to the heatsink and it passes, although it takes a while to get to 0.61v but seems to be functioning fine. I noticed that the ground pin attached to it leads around the board to a very mechanical looking relay in a perspex case with a coil and contacts. I'm wondering if those contacts could have eroded/stuck together.
http://pix.minirig.org.au/main.php?g2_itemId=438&g2_imageViewsIndex=1
That could be quite feasible if the unit had been sitting in someones basement or garage for a few years, prior to being chucked out. Anyone know how to test such a device?
col.
http://pix.minirig.org.au/main.php?g2_itemId=438&g2_imageViewsIndex=1
That could be quite feasible if the unit had been sitting in someones basement or garage for a few years, prior to being chucked out. Anyone know how to test such a device?
col.
just added some more close-up pictures of the area in question.
http://pix.minirig.org.au/main.php?g2_itemId=408&g2_page=2
Mooly, I went and tested all the resistors with their legs showing with power off. They all pretty much measure under 10ohms. There are some bigger resistors that measure up to 0.500k but none of them have gone open circuit.
cheers,
col.
http://pix.minirig.org.au/main.php?g2_itemId=408&g2_page=2
Mooly, I went and tested all the resistors with their legs showing with power off. They all pretty much measure under 10ohms. There are some bigger resistors that measure up to 0.500k but none of them have gone open circuit.
cheers,
col.
The lack of volts over the 6800 mfd cap has to be your starting point. The relay looks (can't say 100% without circuit) like a signal relay, not a power device and it appears not to be in the PSU anyway. You must trace back from the 6800 cap. Someone mentioned regs getting hot. If they are discrete component regs as opposed to IC's ( look at the type numbers 2SDxxxx and 2SA xxxx etc are transistors) and for some unknown reason Jap transistors like this very prone to going open circuit B-E. You would have to measure the DC volt drops with it on. Anything like 22 volts collector 15 volts base and 2 volts emmiter and thats your problem --- definitely worth checking. Anything over 0.7 volts base and emmiter points to a duff device.
Hi Col
I see from your picture 1401 that someone has applied a lot of heatsink compound between that Regulator/Transistor (whatever it is) and the metal bracket. Nakamichi would have made a much neater job of it than that! Has it been replaced before? Big clue here? If it is indeed a 12v reg (**7812) supplying the 6800uF cap, you could perhaps remove it and feed power in from a bench PSU. You could monitor current consumption at the same time, and if something else is wrong with the unit you won't do any further damage.
As I said before, that power-semi gets darn hot, so if & when you get the thing working again don't run it for too long without the back-panel, as I think this helps to heat-sink it!
Regards
Steve
I see from your picture 1401 that someone has applied a lot of heatsink compound between that Regulator/Transistor (whatever it is) and the metal bracket. Nakamichi would have made a much neater job of it than that! Has it been replaced before? Big clue here? If it is indeed a 12v reg (**7812) supplying the 6800uF cap, you could perhaps remove it and feed power in from a bench PSU. You could monitor current consumption at the same time, and if something else is wrong with the unit you won't do any further damage.
As I said before, that power-semi gets darn hot, so if & when you get the thing working again don't run it for too long without the back-panel, as I think this helps to heat-sink it!
Regards
Steve
Just checked the regulator with the power turned on.
I'm getting 23v on the first pin which I think is the collector, 20mv base, 1v Emitter, if that is the right way around.
The device says JRC7812 on it. Which seems to be a standard +12v 1A regulator. In fact, my local electronics shop stocks them as: 7812/LM340T12 +12V fixed 1A TO-220.
It has definitely been changed. Close examination shows side-cutter marks where the legs have been chopped off after soldering. The rest of the components don't exhibit the same technique. Now I'm wondering if it is the correct part or something someone else has tried as a "fix" and failed with.
The component is only $1.25 to purchase so I guess I could just get one and try it. It will be the first money Iv'e spent on it so worth the gamble.
If that doesn't work I'll try supplying power from a independent power supply.
cheers,
col.
I'm getting 23v on the first pin which I think is the collector, 20mv base, 1v Emitter, if that is the right way around.
The device says JRC7812 on it. Which seems to be a standard +12v 1A regulator. In fact, my local electronics shop stocks them as: 7812/LM340T12 +12V fixed 1A TO-220.
It has definitely been changed. Close examination shows side-cutter marks where the legs have been chopped off after soldering. The rest of the components don't exhibit the same technique. Now I'm wondering if it is the correct part or something someone else has tried as a "fix" and failed with.
The component is only $1.25 to purchase so I guess I could just get one and try it. It will be the first money Iv'e spent on it so worth the gamble.
If that doesn't work I'll try supplying power from a independent power supply.
cheers,
col.
Very interesting-- Stevecole was eagle eyed to spot it had been tampered with.
First question do we as you say, assume a 7812 (not a transistor-it's a common voltage reg-- any 7812 will work) is the correct part. Does the middle leg go direct to ground ? It probably will with a 7812 ( buts it's not 100% guaranteed, it could possibly be "lifted" by other components to alter the output voltage ).
Check it!!! If it does I would unsolder pin 3 -- the output -- and switch on and see if that pin now has 12 volts on it. These regs are pretty tough with thermal and overcurrent protection, so it's not likely to have failed again- if it ever was faulty. Are you sure a motor isn't seized- give em a turn by hand. If 12 volts comes up on pin 3 you will have to resolder it back and start lifting items on that line to see what is dragging it down.
First question do we as you say, assume a 7812 (not a transistor-it's a common voltage reg-- any 7812 will work) is the correct part. Does the middle leg go direct to ground ? It probably will with a 7812 ( buts it's not 100% guaranteed, it could possibly be "lifted" by other components to alter the output voltage ).
Check it!!! If it does I would unsolder pin 3 -- the output -- and switch on and see if that pin now has 12 volts on it. These regs are pretty tough with thermal and overcurrent protection, so it's not likely to have failed again- if it ever was faulty. Are you sure a motor isn't seized- give em a turn by hand. If 12 volts comes up on pin 3 you will have to resolder it back and start lifting items on that line to see what is dragging it down.
OK, I've turned all the motors by hand so there is nothing seized. Removed the 7812 regulator bent the output pin up and soldered it back in. Testing it, with the output disconnected, it is showing 1.9v, base 0v and the collector 23v.
I think I will go buy one of these 7812 regulators and give it a shot.
will report back soon.
col.
I think I will go buy one of these 7812 regulators and give it a shot.
will report back soon.
col.
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