Hi jimpkarl,
not at this point. Since we have the feedback loop it is difficult to tell. For now just focus on the Voltage Readings across B-E for each transistor. They should read about 0.6V to 0.75V. Any higher reading than that, the transistor is highly suspect of been blown.
Also, focus on readings C-E, if they read the same or nearly the same voltages, means the transistor is either turn on or internally melted and shorted. In such cases look were the current can flow and check other components that are connected to it.
As I had posted to the link to the other Thread, it seems the STK0039 is the weak spot. Replace these chips first. They show an internal diagram of the STK Chip. This might help you to measure the chip once you have removed it from the board.
Lets focus on one channel first otherwise one might get tangled up in communication.
If you have a Variac Transformer, it helps with troubleshooting so you are not taking a gamble when plugging in the first time with all new components potentially having something missed and blow the new components again.
If not, find a resistor 10-20 Ohm 20W or so or a Lightbulb and connect in series with the main fuse F3. This might help to protect your new STKs in case something is still bad.
Also, it might be wise to check out the Rectifier D301 and temprarely remove fuse F1 and F2 and put a 20Ohm resistor in its place to protect your speakers.
not at this point. Since we have the feedback loop it is difficult to tell. For now just focus on the Voltage Readings across B-E for each transistor. They should read about 0.6V to 0.75V. Any higher reading than that, the transistor is highly suspect of been blown.
Also, focus on readings C-E, if they read the same or nearly the same voltages, means the transistor is either turn on or internally melted and shorted. In such cases look were the current can flow and check other components that are connected to it.
As I had posted to the link to the other Thread, it seems the STK0039 is the weak spot. Replace these chips first. They show an internal diagram of the STK Chip. This might help you to measure the chip once you have removed it from the board.
Lets focus on one channel first otherwise one might get tangled up in communication.
If you have a Variac Transformer, it helps with troubleshooting so you are not taking a gamble when plugging in the first time with all new components potentially having something missed and blow the new components again.
If not, find a resistor 10-20 Ohm 20W or so or a Lightbulb and connect in series with the main fuse F3. This might help to protect your new STKs in case something is still bad.
Also, it might be wise to check out the Rectifier D301 and temprarely remove fuse F1 and F2 and put a 20Ohm resistor in its place to protect your speakers.
Very helpful tips - especially the voltage readings guidlines which I need to sear in my brain for future debugging. Looking at the B/E readings on the left channel, they all seem good as I've marked them. Even checked TR301 ripple filter further down.
I did refer to that IC diagram on the other link. It helped me to confirm that right channel IC being bad with that short between 9-10 but for this left channel IC not sure it indicates anything to me. What is weird is the schematic lists 1.3v for pin 10, yet I'm measuring 28.8v there. All the other pins seems to be in range. (Note Pin 5 value is not listed there nor on the link diagram) As for pin 10 value of 1.3v vs my measured 28.8v, do you think that a typo on the schematic? There's a 35V cap attached by there so that indicates there should be some decent voltage there, doesn't it?
Also of note I checked the audio at pin 1 and now does not sound distorted to me, so thinking the IC chip is going on that channel too - just ordered another.
Did check the D3030 Rectifier putting out 37.8/-37.8 so a point low on voltage but should be fine.
Assume it's safe to just install the left IC only (leaving the right one completely out) and see if left audio is now clear? If so, then can move on to the right channel. I ordered these replacements a couple days apart anyway.
I have a variac but generally unclear how I should be using it. Yes - turn the voltage up slowly, but what should I specifically be checking for as I bring it up?
Hi jimpkarl,
...What is weird is the schematic lists 1.3v for pin 10, yet I'm measuring 28.8v there....
I would guess here something is half dead, no typo. Analog circuits can be crippled and give some "inbetween" results, e.g. half working - half dead.
Using a variac makes things much more safe especially when taking equipment back into operation.
Generally I would suggest to connect an AC Ampere meter in series with the main AC connection so one can read the current consumption of the unit under test while slowly dialing up the variac AC voltage.
The amplifier should be working at about 50% AC voltage, of course the amp will not perform to maximum spec, yet it should be working giving you clear sound at low volume.
While dialing up the variac to full AC voltage I generally monitor continuously all major DC supply voltages in the UUT while also monitoring the AC current consumption.
This is an easy and relaxed way of taking things back into operation while ensuring that everything is fine and no expensive components get blown again if something was missed or is not quite right.
So if you measure more AC current draw than expected while dialing up the AC voltage, something is majorly wrong and you can safely investigate what draws the excessive current and correct the situation.
Also while monitoring the DC voltages you can easily spot trouble before things turn bad on you.
Hope this helps.
...What is weird is the schematic lists 1.3v for pin 10, yet I'm measuring 28.8v there....
I would guess here something is half dead, no typo. Analog circuits can be crippled and give some "inbetween" results, e.g. half working - half dead.
Using a variac makes things much more safe especially when taking equipment back into operation.
Generally I would suggest to connect an AC Ampere meter in series with the main AC connection so one can read the current consumption of the unit under test while slowly dialing up the variac AC voltage.
The amplifier should be working at about 50% AC voltage, of course the amp will not perform to maximum spec, yet it should be working giving you clear sound at low volume.
While dialing up the variac to full AC voltage I generally monitor continuously all major DC supply voltages in the UUT while also monitoring the AC current consumption.
This is an easy and relaxed way of taking things back into operation while ensuring that everything is fine and no expensive components get blown again if something was missed or is not quite right.
So if you measure more AC current draw than expected while dialing up the AC voltage, something is majorly wrong and you can safely investigate what draws the excessive current and correct the situation.
Also while monitoring the DC voltages you can easily spot trouble before things turn bad on you.
Hope this helps.
I built a light bulb protection circuit some time ago, I could run the amp through that then into the variac (or into the variac then into the light bulb if that order makes more sense?)
What do you think the purpose of C233 hanging off pin 10 is? Pretty high voltage rating if the expected voltage is only a volt? Not sure what else in the circuit (beyond the IC chip itself) could be half dead. I had esr meter checked all the caps (10uf and up) and the remaining transistors pass your B/E & C/E tests (but i could pull them anyway and put on a transistor tester for leakage. The only left is to ohm out all the resistors and I had already checked 249 & 251 and they're fine. But if I start with the intended power source (TR301 ripple filter) that emitter is showing 30.2v (spec is 30v) which feeds R247 which show 30v on the other side. Then knocked down a little further by R249 & R251 so I guess I don't understand why 28v at pin 10 is wrong? (these were more recent readings with the left IC in, but right channel IC out since we know that's dead.)
What do you think the purpose of C233 hanging off pin 10 is? Pretty high voltage rating if the expected voltage is only a volt? Not sure what else in the circuit (beyond the IC chip itself) could be half dead. I had esr meter checked all the caps (10uf and up) and the remaining transistors pass your B/E & C/E tests (but i could pull them anyway and put on a transistor tester for leakage. The only left is to ohm out all the resistors and I had already checked 249 & 251 and they're fine. But if I start with the intended power source (TR301 ripple filter) that emitter is showing 30.2v (spec is 30v) which feeds R247 which show 30v on the other side. Then knocked down a little further by R249 & R251 so I guess I don't understand why 28v at pin 10 is wrong? (these were more recent readings with the left IC in, but right channel IC out since we know that's dead.)
Yes, you could do variac + light bulb if it put your mind at rest.
I am not sure what C233 is for. High voltage rating is relative to me, considering you have +/- 39V rails, it seems reasonable, altho I could have used a 50V capacitor perhaps.
Well, the capacitor might see static 1V or so, but as soon as you have an audio signal at high amplitude this capacitor might see more than just a volt.
Usually semiconductors do show in some cases a half dead failure mode. In particular considering you have multiple issues with several semiconductors blown / failed. For now I would have no reason to believe any passive components are bad, unless you find some that have signs of burns and discoloration.
If you feel like checking resistors, just look at the lower resistance values as a 100k resister for example will not burn out on you with 40V...
I would put my money on the semiconductors.
Make sure when you remove capacitors, you pay attention to the correct polarity when re-installing them or bad things will happen...
TR301 ripple filter, emitter @ 30.2v is fine, no problem there.
...don't understand why 28v at pin 10 is wrong...
Don't loose any sleep over it, when component die half way, funny stuff is happening including weird voltage readings.
I am not sure what C233 is for. High voltage rating is relative to me, considering you have +/- 39V rails, it seems reasonable, altho I could have used a 50V capacitor perhaps.
Well, the capacitor might see static 1V or so, but as soon as you have an audio signal at high amplitude this capacitor might see more than just a volt.
Usually semiconductors do show in some cases a half dead failure mode. In particular considering you have multiple issues with several semiconductors blown / failed. For now I would have no reason to believe any passive components are bad, unless you find some that have signs of burns and discoloration.
If you feel like checking resistors, just look at the lower resistance values as a 100k resister for example will not burn out on you with 40V...
I would put my money on the semiconductors.
Make sure when you remove capacitors, you pay attention to the correct polarity when re-installing them or bad things will happen...
TR301 ripple filter, emitter @ 30.2v is fine, no problem there.
...don't understand why 28v at pin 10 is wrong...
Don't loose any sleep over it, when component die half way, funny stuff is happening including weird voltage readings.
OK got two new IC amps installed. Did the left first and reading seem reasonable and channel is working apparently fine. Put the right channel in and although things "sound" fine, they certainly don't measure fine. See attached diagram. Also put the IC chip voltages here since space is tight on the picture.
Pin Reference value Left Right
1 -1.4 -1.2 0
2 -39.1 -38.5 -38.3
3 -0.02 -.16 1.1 ***
4 N/A
5 -38.5 -38 -38
6 N/A
7 N/A
8 0.02 -.15 1.1 ***
9 39.1 37.8 37.8
10 1.3 .86 2.2 ***
In the pic you will see the right channel TR202 has some wacky values as well
PIN Ref Value Left TR201 Right TR202
E .6 .68 1.8
B1 0 0 1.23
B2 0 0 1.22
C1 -36.6 -35 -35
C2 -38 -36 -36
So while the B/E voltage ratio are still "valid", They are way high compared to the reference which shows the B voltage should not be there on TR202. Also the Collector voltage on TR204 is whacked (ref is -6.8 and reading -0.3).
Thoughts?
https://drive.google.com/file/d/0B_Yuh1ijNVjmOUVHZWNLMUFCYjg/view?usp=sharing
Pin Reference value Left Right
1 -1.4 -1.2 0
2 -39.1 -38.5 -38.3
3 -0.02 -.16 1.1 ***
4 N/A
5 -38.5 -38 -38
6 N/A
7 N/A
8 0.02 -.15 1.1 ***
9 39.1 37.8 37.8
10 1.3 .86 2.2 ***
In the pic you will see the right channel TR202 has some wacky values as well
PIN Ref Value Left TR201 Right TR202
E .6 .68 1.8
B1 0 0 1.23
B2 0 0 1.22
C1 -36.6 -35 -35
C2 -38 -36 -36
So while the B/E voltage ratio are still "valid", They are way high compared to the reference which shows the B voltage should not be there on TR202. Also the Collector voltage on TR204 is whacked (ref is -6.8 and reading -0.3).
Thoughts?
https://drive.google.com/file/d/0B_Yuh1ijNVjmOUVHZWNLMUFCYjg/view?usp=sharing
I been through the same problems you are having....
I have done 25 years of bench repair.
Sometimes I got on the phone and asked tech support for help...
and just a few times they put me in the right direction....
Most repairs are cut and dry and your done.... but sometimes you
have to dig and dig till you hit bottom....
And the meaning of those words is.... start from the beginning and check every
part in that circuit... (resistors change value) caps short or change value or I have seen them work ok but just have a few 1000 ohms across them...and that makes the circuit voltages way off !! direct coupled amps are the worst.. one transisitor with even a small leakage will change every voltage in the circuit.. and that makes it hard to find because every voltage is off ! (direct coupled amps sometimes only give you 1 chance)then you start all over....
if in doubt unhook one side of the resistor and measure each and every one...
sometimes it takes a while but in the end you know what is good and what is suspect!!..
it takes work... but in the end... you win.... !!! it will make you better..... stop have some coffee,, drink a pop...take a break,,, if some of the transisitors my be suspect..
just change them...yeah it cost...and your time is worth what??
what made me get through a few repairs is I just dont give up. !!
maybe I should have picked it up and just tossed it in the trash,,
but thats how I ended up owning my own buisness and people asked for me..
I have done 25 years of bench repair.
Sometimes I got on the phone and asked tech support for help...
and just a few times they put me in the right direction....
Most repairs are cut and dry and your done.... but sometimes you
have to dig and dig till you hit bottom....
And the meaning of those words is.... start from the beginning and check every
part in that circuit... (resistors change value) caps short or change value or I have seen them work ok but just have a few 1000 ohms across them...and that makes the circuit voltages way off !! direct coupled amps are the worst.. one transisitor with even a small leakage will change every voltage in the circuit.. and that makes it hard to find because every voltage is off ! (direct coupled amps sometimes only give you 1 chance)then you start all over....
if in doubt unhook one side of the resistor and measure each and every one...
sometimes it takes a while but in the end you know what is good and what is suspect!!..
it takes work... but in the end... you win.... !!! it will make you better..... stop have some coffee,, drink a pop...take a break,,, if some of the transisitors my be suspect..
just change them...yeah it cost...and your time is worth what??
what made me get through a few repairs is I just dont give up. !!
maybe I should have picked it up and just tossed it in the trash,,
but thats how I ended up owning my own buisness and people asked for me..
Thanks for the insight. I agree any one component can cause trouble. However, I'm not particularly fond of a shotgun approach - Take every part out and test it. If you had a problem with your car you wouldn't do that, or an appliance etc. There should be a logical cause or source of the problem, based on circuit readings measured. Now, maybe I don't have even readings taken to make that determination yet, but I have to believe that with the right education is circuit debug (which I don't have which is why I'm here) one would be able to see the circuit reading then narrow down to a particular part of the circuit or even ultimately the offending component to say that is the part(s) to check for failure.
So starting with something like the high base voltages on TR202 (high relative to the expected 0V - where could they be coming from?
Or maybe the easier one to start with is TR204 with a bad collector voltage. Since it should be -6.8v and only seeing -0.3, maybe that part is bad and should be pulled and tested? The only other thing shown hanging off that collector is R234 which can also be easily tested.
Part of the circuit problem solved
OK an updtae. Pulled TR204 and tested. Good with no leaks. So started to look at the connecting components R234, R230, R236. Found Emitter R230 to be completely dead (and actually flaking a bit). Base R236 a little high on tolerance (measured 3K vs 2.7K so replaced that as well just as a precaution. Now have a similar voltage on the Collector at -6v (Similar to left channel one anyway, spec says -6.8v). It was basically zero before with the bad resistor.
So - to learn here - How does the bad emitter resistor R230 affect the Collector voltage?
Next - Still have the strange values on the TR202 Base(s) and Emmiter. Still WAY off the spec. Checked all the connecting resistors and caps (anything above 1uf, I don't have any way to test the pf ones). The transistor appears to be operating correctly (meaning given the base voltage, the emitter voltage is appropriate), but clearly the base voltages should not be that high and I just don't see what might be driving it.
OK an updtae. Pulled TR204 and tested. Good with no leaks. So started to look at the connecting components R234, R230, R236. Found Emitter R230 to be completely dead (and actually flaking a bit). Base R236 a little high on tolerance (measured 3K vs 2.7K so replaced that as well just as a precaution. Now have a similar voltage on the Collector at -6v (Similar to left channel one anyway, spec says -6.8v). It was basically zero before with the bad resistor.
So - to learn here - How does the bad emitter resistor R230 affect the Collector voltage?
Next - Still have the strange values on the TR202 Base(s) and Emmiter. Still WAY off the spec. Checked all the connecting resistors and caps (anything above 1uf, I don't have any way to test the pf ones). The transistor appears to be operating correctly (meaning given the base voltage, the emitter voltage is appropriate), but clearly the base voltages should not be that high and I just don't see what might be driving it.
ok.. your getting close... thats just the approach i was talking about... you just have to start unhooking parts and measuring.. ok.. usually the pf caps are not the cause..
when the resistors are off value it changes the current in the circuit which changes the bias which changes the voltages..and if its direct coupled to the next transistor it will change every reading in the next circuit...
I worked for a large power supply manf for 3 years and I had to be able to fix anything that blew up in the burn chamber..they never threw it away it was fixed. ! I never received them till no one else could fix it...I remember the first time they gave me 2 of them and just said fix them..I replaced all the parts ,, in manf you even have to check to see if its even the correct part in the circuit. hooked it up to my techtronics scope
made some mesurements and the waveforms were almost perfect..?? BUT,,,, the waveform was just a couple volts low...hmmmm..( I had programmed the correct waveform into my scope ) back to work.... found both driver transformers were made incorrect and replaced both on both power supplys..correct scope measurements now...
i marked them like they said and sent them on thier way..
about a week later i had the head testing engineer asking me what I did to fix them...
He said he ran them through the burn chamber 3 times and they passed !!...
at first I told him it was a secret..! then I told him i had programmed in the waveform in my tt scope and measured and changed parts till i had the correct waveform..
and that the driver transformers were all manf with the incorrect windings....
...
every repair will be something new...
I will look at that circuit and leave my thoughts. ohhhh also good luck...i can see your not giving up. !
when the resistors are off value it changes the current in the circuit which changes the bias which changes the voltages..and if its direct coupled to the next transistor it will change every reading in the next circuit...
I worked for a large power supply manf for 3 years and I had to be able to fix anything that blew up in the burn chamber..they never threw it away it was fixed. ! I never received them till no one else could fix it...I remember the first time they gave me 2 of them and just said fix them..I replaced all the parts ,, in manf you even have to check to see if its even the correct part in the circuit. hooked it up to my techtronics scope
made some mesurements and the waveforms were almost perfect..?? BUT,,,, the waveform was just a couple volts low...hmmmm..( I had programmed the correct waveform into my scope ) back to work.... found both driver transformers were made incorrect and replaced both on both power supplys..correct scope measurements now...
i marked them like they said and sent them on thier way..
about a week later i had the head testing engineer asking me what I did to fix them...
He said he ran them through the burn chamber 3 times and they passed !!...
at first I told him it was a secret..! then I told him i had programmed in the waveform in my tt scope and measured and changed parts till i had the correct waveform..
and that the driver transformers were all manf with the incorrect windings....
...
every repair will be something new...
I will look at that circuit and leave my thoughts. ohhhh also good luck...i can see your not giving up. !
ok... not that it will be any help...
D201... even if it checks good replace it......
all the resistors in the gray area are suspect...
I dont think there is always a cut and dry fix by just making voltage measurements..
it never worked for me.....it can put you on the right track,, but from there you have to
check parts...IF you think that is difficult you should try something with lightening damage.. i sometimes worked on them in my sleep !.......
D201... even if it checks good replace it......
all the resistors in the gray area are suspect...
I dont think there is always a cut and dry fix by just making voltage measurements..
it never worked for me.....it can put you on the right track,, but from there you have to
check parts...IF you think that is difficult you should try something with lightening damage.. i sometimes worked on them in my sleep !.......
Hi jimpkarl,
you are making good progress. -6.8V vs. 6.0V difference = 0.8V does this ring a bell ?
If I a may guess again, I would guess something is bad about TR206. Why ?
Emiter of TR206 sees -38V power supply through Resistor R238. The Collector of TR206 is connected to the Chip Amp IC202.
Guessing IC202 was badly blown, it is possible that TR206 has seen briefly +30some Volts from the blown IC202 and could have partially been damaged also.
I would pull and replace TR206. And test again.
EDIT: Oops I just realized you already replaced the blown TR206. I apologize I have not looked at this thread in a while. We established TR206 been dead already.
Well, have a look at Resistor R256 and R254. They should read the same value.
Also, you now have the luxury of a working channel you can make comparison measurements. You could do comparison measurements when powered up and powered down to find the offending component.
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Yeah - I had been doing comparison all along, but now that left ch is working 100% it's a better baseline for sure.
OK - Double checked ALL resistors on that right channel (and the left but more on that later). The only ones hard to verify were the two IC output ones (R256/R254 0.22 ohms) - My meter doesn't do top well in that range and shows .4 ohms for both, but I see the same on the left channel so didn't think that was a major problem. Unfortunately dont' have any replacement on hand to swap out but given what's next, don't think this is it anyway.
*** Then tried something *** Since TR202 had wacky readings, I swapped with TR201 from the left channel. Guess what - MOST (not 100%) of the issues moved with it. Certainly 100% of the IC readings that were out of whack moved as well, and now the right channel IC readings are all fine and the Left IC readings are wrong. Obviously something wrong with TR201 (former TR202) but not clear what and how it affected the IC. Was hoping that part wasn't the problem because it's probably going to be the most difficult for me to replace from what I've read. Basically have to create a new one from two matched substitute parts.
*** However - What's strange is while it fixed the IC readings on the right (and moved them to the left), it *did not* bring along the high voltage B1/B2 base readings that it was experiencing in the right channel See revised attached pic. https://drive.google.com/file/d/0B_Yuh1ijNVjmcGVGWWNKZDMwbjg/view?usp=sharing
TR201 actually looks ok on all sides (whereas when it was in the right channel readings where bad), though Left TR205 has a wacky collector value which I assume is the cause of the wacky IC readings in turn.
I guess that is one of the questions - is TR205 collector affecting the IC201 or is the IC affecting TR205's collector?
Also, if TR201 shows all valid base/emitter/collector values now - how can it be affecting TR205 and/or IC201?
And back to 100% - which I don't think the swap solved. On the right, TR202 has a little higher emitter and a slight (.175) b1/b2 now, MUCH better then before, but not quite right and I've been through basically every part now. Maybe it's just an artifact of left IC going wacky and somehow trying to compensate the right channel, but I also don't recall the reverse happening before the TR201/202 swap either. TR201 has always had a good Emitter and base values, regardless of the part installed.
Confusing. The short summary (in case I lost anyone along the way)
Swapping Right channel TR202 with Left channel TR201:
Reduced substantially (but not eliminated) voltage errors on Right TR202
Eliminated Voltage errors on Right IC202
Caused voltages error on Left IC201
Did not cause voltage errors at Left TR201 position but
Caused Collector voltage errors on Left TR205
OK - Double checked ALL resistors on that right channel (and the left but more on that later). The only ones hard to verify were the two IC output ones (R256/R254 0.22 ohms) - My meter doesn't do top well in that range and shows .4 ohms for both, but I see the same on the left channel so didn't think that was a major problem. Unfortunately dont' have any replacement on hand to swap out but given what's next, don't think this is it anyway.
*** Then tried something *** Since TR202 had wacky readings, I swapped with TR201 from the left channel. Guess what - MOST (not 100%) of the issues moved with it. Certainly 100% of the IC readings that were out of whack moved as well, and now the right channel IC readings are all fine and the Left IC readings are wrong. Obviously something wrong with TR201 (former TR202) but not clear what and how it affected the IC. Was hoping that part wasn't the problem because it's probably going to be the most difficult for me to replace from what I've read. Basically have to create a new one from two matched substitute parts.
*** However - What's strange is while it fixed the IC readings on the right (and moved them to the left), it *did not* bring along the high voltage B1/B2 base readings that it was experiencing in the right channel See revised attached pic. https://drive.google.com/file/d/0B_Yuh1ijNVjmcGVGWWNKZDMwbjg/view?usp=sharing
TR201 actually looks ok on all sides (whereas when it was in the right channel readings where bad), though Left TR205 has a wacky collector value which I assume is the cause of the wacky IC readings in turn.
I guess that is one of the questions - is TR205 collector affecting the IC201 or is the IC affecting TR205's collector?
Also, if TR201 shows all valid base/emitter/collector values now - how can it be affecting TR205 and/or IC201?
And back to 100% - which I don't think the swap solved. On the right, TR202 has a little higher emitter and a slight (.175) b1/b2 now, MUCH better then before, but not quite right and I've been through basically every part now. Maybe it's just an artifact of left IC going wacky and somehow trying to compensate the right channel, but I also don't recall the reverse happening before the TR201/202 swap either. TR201 has always had a good Emitter and base values, regardless of the part installed.
Confusing. The short summary (in case I lost anyone along the way)
Swapping Right channel TR202 with Left channel TR201:
Reduced substantially (but not eliminated) voltage errors on Right TR202
Eliminated Voltage errors on Right IC202
Caused voltages error on Left IC201
Did not cause voltage errors at Left TR201 position but
Caused Collector voltage errors on Left TR205
well actually that makes things clear...
the junctions when damaged change with heat and moving them around because they are damaged inside..........
I know you cant replace every part in the circuit.. resistors can be checked..
caps can be checked diodes are the same as transistors .. they can be checked but unless you have a curve tracer you cant see inside.
! so its not always 100%
I just replace all the driver parts in the circuit including the outputs and check all the diodes and resistors for correct values and change any caps that may be suspect and go from there...
and that insures that channel should work without worry of blowing it up next time you want to run it at med power for an extended time.......
leaving any old predriver or driver transistors are just asking for trouble later... it cost a few dollars more,, but in the end you have something that works and works correct......
the junctions when damaged change with heat and moving them around because they are damaged inside..........
I know you cant replace every part in the circuit.. resistors can be checked..
caps can be checked diodes are the same as transistors .. they can be checked but unless you have a curve tracer you cant see inside.
! so its not always 100%
I just replace all the driver parts in the circuit including the outputs and check all the diodes and resistors for correct values and change any caps that may be suspect and go from there...
and that insures that channel should work without worry of blowing it up next time you want to run it at med power for an extended time.......
leaving any old predriver or driver transistors are just asking for trouble later... it cost a few dollars more,, but in the end you have something that works and works correct......
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Hi jimpkarl,
here is a long list of possible replacement parts for the matched set. These parts are matched by the manufacturer.
Transistors (BJT) - Arrays | Discrete Semiconductor Products | DigiKey
here is a long list of possible replacement parts for the matched set. These parts are matched by the manufacturer.
Transistors (BJT) - Arrays | Discrete Semiconductor Products | DigiKey
Hi jimpkarl,
I found the original part for TR201 (TR202) on UTSource. I just bought from them the other day, they are happy to sell one piece and have very reasonable shipping cost.
2SA798 Datasheet/PDF/Picture,Buy 2SA798 Promotional electronic components at Low Price on Utsource.net
Shown in there listing is the correct part, but somehow the description of it is wrong.
I found the original part for TR201 (TR202) on UTSource. I just bought from them the other day, they are happy to sell one piece and have very reasonable shipping cost.
2SA798 Datasheet/PDF/Picture,Buy 2SA798 Promotional electronic components at Low Price on Utsource.net
Shown in there listing is the correct part, but somehow the description of it is wrong.
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