Earlier today i ordered from Mouser 50 each of KSC1845FTA and KS992FTA. I have only delved into these types of repair recently but have encountered 2SC2240 / A990's. That being so and since you say these replacements are becoming scarce, I thought having some on hand was a good idea should their need arise in future.....and they were cheap.
A bit of a recap....unless I misunderstood, It's OK to use the 2SB817 / 2SD1047 and 2SB649A / 2SD669A that I have coming from Asia?
Also, you wrote:
If the VAS transistors Q413/415 have failed, then that same current path, via Q417, is likely the culprit. D419/417 are high voltage, low current 1SS81 types with only about 200mA current rating - around that of common signal diodes.
Does that mean then that those diodes are likely in good condition? I ask because checking a diode means lifting a lead. I am reluctant to do that without having a new diode on hand. I have not had good luck re-inserting diode leads (or resistor leads for that matter) through the hole without damaging the trace tab on the foil side. Whenever checking a diode was recommended, I felt it was easiest and safest to just replace it but I have none which are suitable. In hindsight I should have ordered some I suppose but there's possibility of finding some locally. I can use those parameters you provided.
A bit of a recap....unless I misunderstood, It's OK to use the 2SB817 / 2SD1047 and 2SB649A / 2SD669A that I have coming from Asia?
Also, you wrote:
If the VAS transistors Q413/415 have failed, then that same current path, via Q417, is likely the culprit. D419/417 are high voltage, low current 1SS81 types with only about 200mA current rating - around that of common signal diodes.
Does that mean then that those diodes are likely in good condition? I ask because checking a diode means lifting a lead. I am reluctant to do that without having a new diode on hand. I have not had good luck re-inserting diode leads (or resistor leads for that matter) through the hole without damaging the trace tab on the foil side. Whenever checking a diode was recommended, I felt it was easiest and safest to just replace it but I have none which are suitable. In hindsight I should have ordered some I suppose but there's possibility of finding some locally. I can use those parameters you provided.
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I see we still have a communication problem and I have confused Fairchild part numbers with KEC. I will keep it plain and simple.
KEC datasheets (dated 2002) refer to KTD1047 and KTB817.
Fairchild parts were last identified as KSD1047 and KSB817.
Original Sanyo parts were identified as 2SD1047 and 2SB817.
The seller refers to the Sanyo Part numbers, which can't be correct.
The parts are just marked D1047 or B817, so I cannot say what spec. they refer to. I guess you can use them based on the word of the seller. I have never seen this style of KEC marking before, so honestly, I can't give you assurances.
The diodes.
I meant that you can usually test an isolated diode failure easily, even in-circuit:
If the diode is shorted, its resistance will read like a piece of wire, in either direction. If it is open-circuit, it will probably have some high resistance in both directions. When a diode fails, a short is far more likely, so assuming it works, you look for the O.7V diode voltage with your meter's diode checker, used in both directions if you can't remember which way current flows.
There are a number of replacements but not all are available with leads or in small quantities. You could use 120 or 150V types or more and up to 500 mA rated, standard recovery switching diodes if you need to.
KEC datasheets (dated 2002) refer to KTD1047 and KTB817.
Fairchild parts were last identified as KSD1047 and KSB817.
Original Sanyo parts were identified as 2SD1047 and 2SB817.
The seller refers to the Sanyo Part numbers, which can't be correct.
The parts are just marked D1047 or B817, so I cannot say what spec. they refer to. I guess you can use them based on the word of the seller. I have never seen this style of KEC marking before, so honestly, I can't give you assurances.
The diodes.
I meant that you can usually test an isolated diode failure easily, even in-circuit:
If the diode is shorted, its resistance will read like a piece of wire, in either direction. If it is open-circuit, it will probably have some high resistance in both directions. When a diode fails, a short is far more likely, so assuming it works, you look for the O.7V diode voltage with your meter's diode checker, used in both directions if you can't remember which way current flows.
There are a number of replacements but not all are available with leads or in small quantities. You could use 120 or 150V types or more and up to 500 mA rated, standard recovery switching diodes if you need to.
Don't buy transistors from Ebay, they are guaranteed to be fake. You're wasting time and money here. 🙁
Since I have already paid for those transistors from Hong Kong I shall use them and hope for the best. Neither Mouser, Digikey, or Newark Element 14 (the only North American online vendors I'm aware of) had KEC or Fairchild 1047/817 so I'm going to take my chances. Unless I was using those supplier's product finder incorrectly, entering specs led to the same part numbers (in Mouser's case) or "out of stock - obsolete - none found".
Although no guarantee, I am made somewhat confident by the vendor's greater than 27,000 transactions plus 99.6% positive feedback score. I checked the negative's and of those I examined, nearly all had to do with shipping & returns, very few involved a complaint of the actual item.
There are 4 1SS81 diodes on the board D417/418/419/420) and I checked them all in circuit. Although less than 0.7 volts, 3 of the 4 seemed OK with readings of .54 volts in one direction and OL in the other. D418 was the exception which allowed voltage both ways .54 volts and .43 volts. There are 3 local electronics parts vendors I've purchased from and I hope to visit them in the next day or so. I shall ask for 1SS81 first but if not available, I'll use the that description:
"....120 or 150V types or more and up to 500 mA rated, standard recovery switching diodes....".
It looks like I can go higher in voltage but the 500 mA rated current must not be exceeded? Looking at one local suppliers website, it appears that high speed recovery rather than standard recovery are more prevalent
Although no guarantee, I am made somewhat confident by the vendor's greater than 27,000 transactions plus 99.6% positive feedback score. I checked the negative's and of those I examined, nearly all had to do with shipping & returns, very few involved a complaint of the actual item.
There are 4 1SS81 diodes on the board D417/418/419/420) and I checked them all in circuit. Although less than 0.7 volts, 3 of the 4 seemed OK with readings of .54 volts in one direction and OL in the other. D418 was the exception which allowed voltage both ways .54 volts and .43 volts. There are 3 local electronics parts vendors I've purchased from and I hope to visit them in the next day or so. I shall ask for 1SS81 first but if not available, I'll use the that description:
"....120 or 150V types or more and up to 500 mA rated, standard recovery switching diodes....".
It looks like I can go higher in voltage but the 500 mA rated current must not be exceeded? Looking at one local suppliers website, it appears that high speed recovery rather than standard recovery are more prevalent
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We can't generalise that all Ebay semis are fakes. Some Ebay stores indeed sell bad copies and some fakes but many parts sold are also genuine OEM, some second-source, some just poor copies due to generic chip substitutions too. If we see large quantities of parts being offered cheap, it does not mean fake either, though it's unlikely to be genuine branded product or spec.
Like others here, I realise that many small Ebay sellers clearly don't care what they sell or understand what makes it acceptable quality. Most seem to offer similar ranges of fashion items, leisure goods as well as electronic toys, tools and components. The owner opens a store, sells enough to close and open another with a different identity and so avoid a bad rating. Yet others seem to be in a permanent electronic components business.and traded for several years in a large stock inventory of similar quality components to those used widely in Chinese manufactured electronics. The products are well known to us and are in any consumer household, globally.
I have bought KEC product for example, for 30 years through several suppliers, now including Ebay stores and been very impressed with quality. On the other hand, I've bought "genuine" Motorola, Toshiba, Philips and Siemens semis from reputable, global suppliers and agents that proved to be fake, long before Ebay or the internet existed.
The alternative; to bin an amplifier because suitable original components are obsolete, too expensive or unobtanium, is just careless IMV. Basic semis can be freely substituted within the general specification requirements, knowing that the originals were not unique or essential but specified on price and availability. Sure, an engineering analysis and understanding is often needed to be certain of choices and any necessary adjustments but previous experience can be useful too 🙂
1SS81 is a standard recovery silicon diode, like a higher voltage version of the very common IN4148. Let's stay close to original if possible.
The voltage and current ratings should be ≥ the part it replaces. I suggest you don't use much higher current ratings because diodes can pass very short, high current pulses which can do worse damage in a fault condition. A 1N4003-1N4007 rectifier diode, for example, is rated at 1A continuous but can pass a single pulse of 30A 😱 The 1N4148 is rated at 200mA continuous but can pass a 4A single pulse. Different sources may have different voltage ratings like 75V (old Philips) or 100V (NXP, On-Semi etc.) but still not enough for this amplifier.
1N4148 or 1N914 are by far the most common standard diodes and why they are usually all you can buy for signal diodes in small parts shops. With a little more voltage rating, they would be ok. BAV20 or BAV21 are less common but would be just fine. I doubt you will find Japanese spec. standard diodes like 1SS81 and you don't really need them but some specialist parts importers may stock them.
Fast, ultra fast recovery and Schottky types are for modern switch-mode power supplies and high current commutating applications - not what is needed here and the smaller types are usually low voltage too.
I could be wrong in that those types may be acceptable if current and voltage ratings were also sensible. Perhaps an expert would care to comment.
It's too bad that IN400X diodes aren't suitable because I can get them by the boot full around here. But you are correct about BAV20/21 - no such animal locally. I'll order some but probably won't receive until next week. They look to be rated at 200ma so definitely OK to use?
Don't sweat this, signal diodes are not critical or particularly accurate parts. They just need to have enough voltage and current capacity to exceed the maximum duty comfortably. The datasheets are often slightly different for each manufacturer, but that won't be problem with the real parts. Here is an example, which shows the 200mA average current rating:
1SS81 datasheet(1/2 Pages) KISEMICONDUCTOR | SMALL SIGNAL SWITCHING DIODE
If you want to vet products, just Google the part number, adding "datasheet" and the rest is a matter of deciding on a good site. I use Datasheetcatalog.com where possible because it offers a range of manufacturers and minimal ads 🙂
1SS81 datasheet(1/2 Pages) KISEMICONDUCTOR | SMALL SIGNAL SWITCHING DIODE
If you want to vet products, just Google the part number, adding "datasheet" and the rest is a matter of deciding on a good site. I use Datasheetcatalog.com where possible because it offers a range of manufacturers and minimal ads 🙂
No question I obcess but also have next to no intimate knowledge of electronic parts so I also tend to be overly cautious. Not when it comes to anything consequential, just past times - much to my detriment.
As anticipated I was nearby 2 parts stores this morning. One had IN4001 so I got a few on the off chance they might work plus they were cheap. The second shop has A LOT of NOS and obscure parts so I thought 1SS81 might be a possibility but no. They did order me some BAV20's which they say I shall have on Friday.
Doubtful but maybe the transistors will show up this week so I can have something other than practical chores to do this weekend.
As anticipated I was nearby 2 parts stores this morning. One had IN4001 so I got a few on the off chance they might work plus they were cheap. The second shop has A LOT of NOS and obscure parts so I thought 1SS81 might be a possibility but no. They did order me some BAV20's which they say I shall have on Friday.
Doubtful but maybe the transistors will show up this week so I can have something other than practical chores to do this weekend.
I did not want to appear to have abandoned this thread.
Last night I installed the BUV20 diodes in place of the 1SS81's and same for the KSC1845FTA / KS992FTA transistors now in place of 2SC2240 / 2SA990's. Once removed, I checked the latter out of circuit and all four seemed to be have been OK.
So now with those new components in place, the DBT glowed brightly as it had before on initial turn on but instead of decreasing to no glow as it did with the original components in place, it dims to about half brightness and remains there.
The power transistors are still out and the R471/R472 solder bridges are still open. I could be wrong here but as I understand it, the DBT should dim to just a faint glow after initial turn on? Do I take this half brightness to mean there's now a short somewhere or is it the nature of this NAD?
I think the power transistors will land this week. One vendor provided a tracking number and that order is the US now. I'm going to assume likewise for that from the second vendor.
At this point it seemed a good idea to check Q413/14/15/16 B-E volts as you had me do before but I only managed as far as Q413 which was .8 volts. What happened next was distressing.
A short time after turning power on again to check another transistor, there was some smoke and 2 "snapping" noises. I left the heat sink sit loose inside and believe it may have contacted pin YE1. So far I've seen resistors R467 and R466 burnt and possibly R449. I did not see any evidence of scorching to the heat sink or pin YE1 but they were in close proximity.
My work space is the dining table and I had the case standing on end, manipulating it side to side frequently to access both sides of the board. Although I cannot say for certain the heat sink shorting on something was the cause, it was careless to leave it free to move so to me it seems likely.
My thought now is to replace R466/467 and R449/450, remove completely or insulate the heat sink and check those B-E voltages again and hope the collateral damage was not more extensive. Oddly, at least I thought so, was that none of the fuses blew. I checked all six for continuity and they are fine.
Last night I installed the BUV20 diodes in place of the 1SS81's and same for the KSC1845FTA / KS992FTA transistors now in place of 2SC2240 / 2SA990's. Once removed, I checked the latter out of circuit and all four seemed to be have been OK.
So now with those new components in place, the DBT glowed brightly as it had before on initial turn on but instead of decreasing to no glow as it did with the original components in place, it dims to about half brightness and remains there.
The power transistors are still out and the R471/R472 solder bridges are still open. I could be wrong here but as I understand it, the DBT should dim to just a faint glow after initial turn on? Do I take this half brightness to mean there's now a short somewhere or is it the nature of this NAD?
I think the power transistors will land this week. One vendor provided a tracking number and that order is the US now. I'm going to assume likewise for that from the second vendor.
At this point it seemed a good idea to check Q413/14/15/16 B-E volts as you had me do before but I only managed as far as Q413 which was .8 volts. What happened next was distressing.
A short time after turning power on again to check another transistor, there was some smoke and 2 "snapping" noises. I left the heat sink sit loose inside and believe it may have contacted pin YE1. So far I've seen resistors R467 and R466 burnt and possibly R449. I did not see any evidence of scorching to the heat sink or pin YE1 but they were in close proximity.
My work space is the dining table and I had the case standing on end, manipulating it side to side frequently to access both sides of the board. Although I cannot say for certain the heat sink shorting on something was the cause, it was careless to leave it free to move so to me it seems likely.
My thought now is to replace R466/467 and R449/450, remove completely or insulate the heat sink and check those B-E voltages again and hope the collateral damage was not more extensive. Oddly, at least I thought so, was that none of the fuses blew. I checked all six for continuity and they are fine.
Hi
The main power supply AC fuses protect both amplifiers and have ratings of 5 and 4A, so you won't blow those whilst ever the DBT is fitted. Remember that it limits mains supply current to the bulb's rated current. Using a 100W bulb, and 60VAC total secondary voltage, the transformer can't deliver more than 1.7A @ 30-0-30VAC with full brightness. The higher, 50-0-50VAC windings would not have much current demand in the situation but their output would just limit further.
There is certainly some difference since you last powered up. Assuming your tests on the replaced and replacement small transistors and diodes are correct and they were actually ok, this new problem shouldn't be with them.
With the power transistors removed, (and I assume you removed all 4 output transistors in the L? channel before powering up again) the current drawn by the power amplifiers should be quite small, so we wouldn't expect the supply current to increase now. It could be that the short you described caused more damage, as you think. Unfortunately, the 71V rails need to be in place to operate the amplifier. I had hoped they could be disconnected for basic testing but this type of "PE" design needs them along with the 43V supplies and main output transistors too.
What you can do is check and compare the voltage drop across fusible resistors R465, 467 to R466, 468 in the other channel. These isolate the front end supply rails from the output stage and the calculated current or simply the voltage, can be compared. If similar, then you know with some certainty, the fault still lies in the output stage - i.e. the section to the right side of Q419,421 in the schematic. While you are in there you might check the other fusible resistors. (identified by
) They are designed to melt or disintegrate quickly in a fault condition, rather than glow, burn or explode and become a safety hazard. NAD 7240PE - Manual - Stereo Receiver - HiFi Engine
The L channel drivers are Q423, 425 and as mentioned earlier, there are indicative voltages shown on the schematic to aid in checking functionality throughout. Look at those around Q417,419,421. Compare with Q418,420,421. The R channel may be bad too but could be useful for reality checks. Take care though, considering you don't need 2 dead channels, both just getting trashed. On that point, don't replace any more semis on the other channel until you have this one working working reliably. Otherwise, you have no reference if you later discover that replacements were not working as well as you thought, for example.
When testing, if you have probe hooks or clip leads, use them at least on the common probe, rather than try to hold both probes in place whilst your attention is on the meter. Slips can easily result in shorts, however brief, and so more parts failures. If you have no work aids like this, tack solder the probe temporarily to a terminal or similar - anything to goof-proof testing which, when you are dickering about with dozens of test points and locations on a powered board, can be just as hazardous as dropping screws or metal parts on it.
The plan, when the idle current changes, is to find what caused it, by tracing where the new or unexpected current demand is. You can find it by checking resitor and semiconductor voltage drops in the current path to them, then calculating current. Just mentally will suffice, if you are used to that, as many pre-calculator guys are. A simple power amplifier will draw very little current, - in the order of 20mA, with the output transistors removed. The bias current for a class AB output stage will increase that when the output transistors are restored, which could be anything from 15-100 mA or more for each channel, depending on the design.
There are a few ways to track fault currents, often just using the existing circuit resistors but you will need to study the amplifier operation if you have to deduce what is still OK and you don't have a good channel for comparison. As you find, DC amplifier measurements don't necessarily identify any nearby part as the culprit, when the fault could just as easily originate in another location. You would need to read and understand the schematic to some level, to see the relationship between all associated components, and check for failures systematically. That will save on lots of unnecessary and repeat parts buying. Fault location is not easy in more complex circuits like this one and you could need more help than my humble thoughts.
The main power supply AC fuses protect both amplifiers and have ratings of 5 and 4A, so you won't blow those whilst ever the DBT is fitted. Remember that it limits mains supply current to the bulb's rated current. Using a 100W bulb, and 60VAC total secondary voltage, the transformer can't deliver more than 1.7A @ 30-0-30VAC with full brightness. The higher, 50-0-50VAC windings would not have much current demand in the situation but their output would just limit further.
There is certainly some difference since you last powered up. Assuming your tests on the replaced and replacement small transistors and diodes are correct and they were actually ok, this new problem shouldn't be with them.
With the power transistors removed, (and I assume you removed all 4 output transistors in the L? channel before powering up again) the current drawn by the power amplifiers should be quite small, so we wouldn't expect the supply current to increase now. It could be that the short you described caused more damage, as you think. Unfortunately, the 71V rails need to be in place to operate the amplifier. I had hoped they could be disconnected for basic testing but this type of "PE" design needs them along with the 43V supplies and main output transistors too.
What you can do is check and compare the voltage drop across fusible resistors R465, 467 to R466, 468 in the other channel. These isolate the front end supply rails from the output stage and the calculated current or simply the voltage, can be compared. If similar, then you know with some certainty, the fault still lies in the output stage - i.e. the section to the right side of Q419,421 in the schematic. While you are in there you might check the other fusible resistors. (identified by
) They are designed to melt or disintegrate quickly in a fault condition, rather than glow, burn or explode and become a safety hazard. NAD 7240PE - Manual - Stereo Receiver - HiFi EngineThe L channel drivers are Q423, 425 and as mentioned earlier, there are indicative voltages shown on the schematic to aid in checking functionality throughout. Look at those around Q417,419,421. Compare with Q418,420,421. The R channel may be bad too but could be useful for reality checks. Take care though, considering you don't need 2 dead channels, both just getting trashed. On that point, don't replace any more semis on the other channel until you have this one working working reliably. Otherwise, you have no reference if you later discover that replacements were not working as well as you thought, for example.
When testing, if you have probe hooks or clip leads, use them at least on the common probe, rather than try to hold both probes in place whilst your attention is on the meter. Slips can easily result in shorts, however brief, and so more parts failures. If you have no work aids like this, tack solder the probe temporarily to a terminal or similar - anything to goof-proof testing which, when you are dickering about with dozens of test points and locations on a powered board, can be just as hazardous as dropping screws or metal parts on it.
The plan, when the idle current changes, is to find what caused it, by tracing where the new or unexpected current demand is. You can find it by checking resitor and semiconductor voltage drops in the current path to them, then calculating current. Just mentally will suffice, if you are used to that, as many pre-calculator guys are. A simple power amplifier will draw very little current, - in the order of 20mA, with the output transistors removed. The bias current for a class AB output stage will increase that when the output transistors are restored, which could be anything from 15-100 mA or more for each channel, depending on the design.
There are a few ways to track fault currents, often just using the existing circuit resistors but you will need to study the amplifier operation if you have to deduce what is still OK and you don't have a good channel for comparison. As you find, DC amplifier measurements don't necessarily identify any nearby part as the culprit, when the fault could just as easily originate in another location. You would need to read and understand the schematic to some level, to see the relationship between all associated components, and check for failures systematically. That will save on lots of unnecessary and repeat parts buying. Fault location is not easy in more complex circuits like this one and you could need more help than my humble thoughts.
This morning I removed the heat sink from the chassis and a little later, received notification that the output transistors have arrived and are ready for pickup. A short time ago, after arriving home from work, my plan was to begin checking the components you indicated. I printed the posting, highlighting the devices in question for ease of reference, My "work station" is the dining table, my computer is in the kitchen.
The first thing I did was turn on the power. The DBT glowed brightly at first then settled down to a glow dimmer than the half brightness it exhibited before. This I though was a good sign. Unfortunately, what followed was wispy smoke but I could not pick out from where - the smoke was just there. I turned off the power, had a look at the board and saw more discolored resistors. I have not scrutinized closely enough yet to identify all of them, I'll do that in the morning when I am not so fatigued.
What I'll likely do tomorrow is power up again (maybe all the smoke that is to be created has already happened) then measure the voltages and document the numbers across all the fusible resistors. I am hoping that any smoke was produced by them and not semi conductors.
The first thing I did was turn on the power. The DBT glowed brightly at first then settled down to a glow dimmer than the half brightness it exhibited before. This I though was a good sign. Unfortunately, what followed was wispy smoke but I could not pick out from where - the smoke was just there. I turned off the power, had a look at the board and saw more discolored resistors. I have not scrutinized closely enough yet to identify all of them, I'll do that in the morning when I am not so fatigued.
What I'll likely do tomorrow is power up again (maybe all the smoke that is to be created has already happened) then measure the voltages and document the numbers across all the fusible resistors. I am hoping that any smoke was produced by them and not semi conductors.
It's unusual for components to burn out when the project is started on a Mains Bulb Tester.
Use a low value incandescent bulb try <<100W, maybe 40W
I keep a range from 25W to 150W to test the wiring on low power through to very high power projects.
Use a low value incandescent bulb try <<100W, maybe 40W
I keep a range from 25W to 150W to test the wiring on low power through to very high power projects.
Taking note of your pointing out that damage can extend beyond the obvious, I have been studying the schematic diagram, PCB layout diagram, parts list and your last very concise post. And although I have not completed the check list, I may have discovered something.
R456 and R455 are also burnt. Unless I am mistaken, they should be receiving 43 volts but what I got when measuring them was 100 volts across R456 and 89 volts across R455. With regards to R456, can it be receiving 100 volts through Q424? Would you agree this high voltage means bridge diode BD501 is damaged? I cannot fathom where else it could be coming from.
With that amount of voltage "coursing through the veins" I guess it's fair to think a good number of transistors (and perhaps diodes) have succumbed? I have yet to check the transistors you indicated but will do so as soon as time allows.
Something I observed. From the parts list, I wrote out a list of what were identified as fusible resistors. On the amplifier board, they were R465, R467, R468, R507 and R508. While looking on the actual board for those numbers I noticed R456 and R455 were also burnt, raised resistors. It seems they too are fusible but the parts list does not say they are.
I should mention that I did measure across R465, R467, R468, R507, R508 and got nowhere near what the schematic said. All voltages were less than 10% of what they should have been.
R456 and R455 are also burnt. Unless I am mistaken, they should be receiving 43 volts but what I got when measuring them was 100 volts across R456 and 89 volts across R455. With regards to R456, can it be receiving 100 volts through Q424? Would you agree this high voltage means bridge diode BD501 is damaged? I cannot fathom where else it could be coming from.
With that amount of voltage "coursing through the veins" I guess it's fair to think a good number of transistors (and perhaps diodes) have succumbed? I have yet to check the transistors you indicated but will do so as soon as time allows.
Something I observed. From the parts list, I wrote out a list of what were identified as fusible resistors. On the amplifier board, they were R465, R467, R468, R507 and R508. While looking on the actual board for those numbers I noticed R456 and R455 were also burnt, raised resistors. It seems they too are fusible but the parts list does not say they are.
I should mention that I did measure across R465, R467, R468, R507, R508 and got nowhere near what the schematic said. All voltages were less than 10% of what they should have been.
Where I live, incandescent bulbs are frowned upon. The ecologically minded of those who exert control over such things wish to make everybody switch to florescent or now I suppose, LED. I only have the one 100W one and a spare appliance bulb for the refrigerator. I've seen them in thrift stores so will pick up some 40's & 60's the next time I see them.
No, the outputs are removed. There are replacements waiting for me to pick up but I will not be installing them until it's safe to do so.
Let's have a look at the rest of the output stage since the output transistors have variable collector voltages, switched up to +/- 70V on peak signal levels. I was puzzled by an apparent short to R471/472 on the schematic but this is a necessary part of the alignment procedure on page 5 of the service manual (linked at post #31).
If something is also wrong with the rail switching (quite likely since it is series with output stage), the normal -/+43V collector voltages could be wrong too. Assuming they are still in-circuit, check the terminal voltages on D1062/B826 too and post here, if you can.
If something is also wrong with the rail switching (quite likely since it is series with output stage), the normal -/+43V collector voltages could be wrong too. Assuming they are still in-circuit, check the terminal voltages on D1062/B826 too and post here, if you can.
BTW, since CFL lamps are now also frowned on, halogen or LED types may be all that fits standard light sockets. Halogen bulbs are incandescent too and also work as DBTs. Common ratings are 28,42,53W here but can be paralleled for more. Canadian prices seem expensive unless you bulk-buy though.
I read your replies first thing this morning but there is no D1062 or B826 in the service manual or on the board that I can see. Did you mean instead output transistors D1067 and B817? If so, they are removed. The replacements are waiting at the package depot and I shall obtain them Saturday.
In the meantime, in order to check voltages, should I re-attach the original transistors? I did not mark which came from the left and right channels. I can measure the voltages at the pads sans transistors if that would be of value.
I doubt installing installing new output transistors at this point and then checking voltages is what you had in mind is it?
That short you pointed out or as the SM calls it "solder bridge" is and has been open since the beginning.
With regards to incandescent bulbs. I pass by thrift stores daily and can easily check for 40 & 60 watt bulbs so fairly sure I can have some later today.
In the meantime, in order to check voltages, should I re-attach the original transistors? I did not mark which came from the left and right channels. I can measure the voltages at the pads sans transistors if that would be of value.
I doubt installing installing new output transistors at this point and then checking voltages is what you had in mind is it?
That short you pointed out or as the SM calls it "solder bridge" is and has been open since the beginning.
With regards to incandescent bulbs. I pass by thrift stores daily and can easily check for 40 & 60 watt bulbs so fairly sure I can have some later today.
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