Chris,
To clarify. The diode test was done on the supposedly fried bias transistor, the 2N5232, not the 2N5087s.
And the new diff pair transistors did not blow. They're still good and had hFE readings (for what it's worth) of 350 and 335 respectively...
Hey something else....when I first plugged in the amp after the new diff pair was in, the fuse blew for the right channel. Could this be caused by a faulty part on the PCB or something else?
To clarify. The diode test was done on the supposedly fried bias transistor, the 2N5232, not the 2N5087s.
And the new diff pair transistors did not blow. They're still good and had hFE readings (for what it's worth) of 350 and 335 respectively...
Hey something else....when I first plugged in the amp after the new diff pair was in, the fuse blew for the right channel. Could this be caused by a faulty part on the PCB or something else?
Hi Paco,
If the other "good" channel failed, something had to happen to it. Solder splash or cut wire end, a speaker wire short could do this also. When something is wrong, the circuit will normally act up as soon as power is applied.
-Chris
So, you're telling me that transistor was shorted E-B and not E-C? If the E-C is not shorted, then there would have been no bias control. That would tend to blow the outputs very quickly.
Case temperature differences would change these numbers quite a bit. A good beta range though, they are about what I measure.
That's why I was thinking your new parts were measuring as bad.
Are we working on the left channel, or the right channel?
If the other "good" channel failed, something had to happen to it. Solder splash or cut wire end, a speaker wire short could do this also. When something is wrong, the circuit will normally act up as soon as power is applied.
-Chris
The bias transistor measured just as I've said. I'm not sure where E-C not being shorted came from... According to what I've read, both E-C and E-B on that one transistor are shorted since they read significantly lower than they should, I think.
If the beta/hFE is good, then I must have messed up somewhere. If beta = Ic/Ib, and Ib was zero, then ,I don't know, the universe would implode or something right?
We're working on the right channel still as always. The first time I plugged the amp in, the right channel fuse blew and some smoke poured out of the bias transistor. So I swapped fuses again and the same thing happened, which I guess was the swan song of that little transistor. When I applied power again with a 5 watt resistor in place of a fuse, nothing happened and so here I am now. This was all after having put in the new diff pair transistors.
If the beta/hFE is good, then I must have messed up somewhere. If beta = Ic/Ib, and Ib was zero, then ,I don't know, the universe would implode or something right?
We're working on the right channel still as always. The first time I plugged the amp in, the right channel fuse blew and some smoke poured out of the bias transistor. So I swapped fuses again and the same thing happened, which I guess was the swan song of that little transistor. When I applied power again with a 5 watt resistor in place of a fuse, nothing happened and so here I am now. This was all after having put in the new diff pair transistors.
Hi Paco,
Thank you. It's hard to remember all the details spread out over time.
You had high current flow before the bias transistor smoked. A short or high leakage in any of Q703, Q705 or Q709 could cause this. Check also R709, R721 and R727 for overheating or value change.
It looks like CR 5 needs careful testing. If you diode test function can put 3 V across it, you should measure 2 diode drops. If you measure a short, the bias diode is dead. I hope it's fine.
-Chris
Thank you. It's hard to remember all the details spread out over time.
You had high current flow before the bias transistor smoked. A short or high leakage in any of Q703, Q705 or Q709 could cause this. Check also R709, R721 and R727 for overheating or value change.
It looks like CR 5 needs careful testing. If you diode test function can put 3 V across it, you should measure 2 diode drops. If you measure a short, the bias diode is dead. I hope it's fine.
-Chris
Hi Paco,
I'm confused now.
When you use the diode test, you should get some voltage drop across a forward biased junction. Expect 565 mV or there about depending on the test current. When you measure beta, you will not get a reading for voltage drop across the junction, but rather the factor between base current and emitter current.
-Chris
I'm confused now.
When you use the diode test, you should get some voltage drop across a forward biased junction. Expect 565 mV or there about depending on the test current. When you measure beta, you will not get a reading for voltage drop across the junction, but rather the factor between base current and emitter current.
-Chris
Chris,
I too am a bit confused/frustrated. I'll try to explain this as best as I can.
When I was testing the 2N5087s for the diff pair, the ones I ended up using had 0V passing through the base when there was a 2k ohm resistor in between the transistor and the test point. This setup was running off of a 9V battery. However, when I used the part tester I just got, for each transistor, it read hFEs of 335 and 350. My question is this; if the beta passes no voltage to begin with, there wouldn't be any hFE would there? The way I see it is that since hFE=Ic/Ib where Ib=Vb/Rb=0 if the voltage is 0, then hFE=Ic/0 which can't happen. I hope this makes sense.
Also, I checked most of the parts you told me to. Here's what I got.
R709 - 433 ohms
R721 - broke in half when I was unsoldering it....
R727 - 100.4 ohms
Q703 - Diode tests: E-C and E-B both got nothing. Leakage got nothing. hFE was 52
Q705 - All tests bounced around and then settled back to 0...
Haven't tested Q709 since it would probably do the same thing as Q705
I too am a bit confused/frustrated. I'll try to explain this as best as I can.
When I was testing the 2N5087s for the diff pair, the ones I ended up using had 0V passing through the base when there was a 2k ohm resistor in between the transistor and the test point. This setup was running off of a 9V battery. However, when I used the part tester I just got, for each transistor, it read hFEs of 335 and 350. My question is this; if the beta passes no voltage to begin with, there wouldn't be any hFE would there? The way I see it is that since hFE=Ic/Ib where Ib=Vb/Rb=0 if the voltage is 0, then hFE=Ic/0 which can't happen. I hope this makes sense.
Also, I checked most of the parts you told me to. Here's what I got.
R709 - 433 ohms
R721 - broke in half when I was unsoldering it....
R727 - 100.4 ohms
Q703 - Diode tests: E-C and E-B both got nothing. Leakage got nothing. hFE was 52
Q705 - All tests bounced around and then settled back to 0...
Haven't tested Q709 since it would probably do the same thing as Q705
Hi Paco,
Which outputs are bad? Test R731 and R735 (0.27 ohm, 5 watt, wire wound).
It's all logic. You are starting to catch on. See how the logic works? I can't actually see or smell the parts, so I am operating with less than 1/2 the clues I would normally see. Some of what I have said may be in error if the information from you is a little off. Just try again.
Testing transistors can be tricky. You have polarity and lead pin out to worry about.
-Chris
My jig? I need a reference to answer your questions.
Then they are good. It's possible you had the transistors reverse biased in the first test.
Either it's bad or you had a bad connection. Meter could be lying to you. If the resistor is truly bad, then Q703 is open E-B (bad).
Probably cracked to begin with due to excessive heat (excessive current flow, condemning Q709 as well).
I would expect that. This resistor did not pass excessive current, so Q705 would also be undamaged. See how this is working? We are tracing the fault currents.
I don't trust this unless R709 was an old carbon composition type at 20% tolerance. For the cost of this part, replace it as well.
Probably a bad connection or incorrect polarity. I would expect this part to be good. Have another look at it and review PNP and NPN transistors. This one is PNP.
I disagree, if anything you should read a short or leakage. If this part managed to survive, I don't think it can be trusted. Test it just for information sake, but replace it anyway.
Which outputs are bad? Test R731 and R735 (0.27 ohm, 5 watt, wire wound).
It's all logic. You are starting to catch on. See how the logic works? I can't actually see or smell the parts, so I am operating with less than 1/2 the clues I would normally see. Some of what I have said may be in error if the information from you is a little off. Just try again.
Testing transistors can be tricky. You have polarity and lead pin out to worry about.
-Chris
I was afraid to tell you this, but no not your jig. I looked for a much simpler way out (which may end up costing more in the end) and used this The specific thing is the red one on the right, for PNP transistors. Voltages were measured across the base and collector resistors.
Should I replace R709?
Got replacements for R721...will have to be 3.2 ohms since I bought resistors from a local store.
I was planning on replacing Q703 and Q707
Hmmm. Ok. Looked around, where could I find a replacement for Q705?
Ok. I'll go through and check parts, see what's what. Also, I did a diode test on CR5 and got 1.817 in the forward direction and nothing for the reverse direction. CR6 (left channel diode) read about the same.
Should I replace R709?
Got replacements for R721...will have to be 3.2 ohms since I bought resistors from a local store.
I was planning on replacing Q703 and Q707
Hmmm. Ok. Looked around, where could I find a replacement for Q705?
Ok. I'll go through and check parts, see what's what. Also, I did a diode test on CR5 and got 1.817 in the forward direction and nothing for the reverse direction. CR6 (left channel diode) read about the same.
Hi Paco,
You can find any number of things on the 'Net. It's up to you to sort out the rubbish from useful stuff. If the guy doesn't understand the importance of matching parts, he really doesn't know how amplifiers work. It's really as simple as that. So, yes his amp works, but it doesn't work "fine". It does function. That's the difference between knowledge and thrashing about with a partial clue.
So you are using the thing running off 15 VDC in the diagram, you are using a 9V battery? The battery is fine by the way. Please tell me precisely where you are measuring your voltages, give me the resistor value you are measuring across.
BTW, this setup will not really allow you to match transistors. You have no way to control the device temperature. The jig I posted cancels out the temperature issue and you are left measuring differential voltages. So it works by indicating a match at any reasonable temperature, and you can vary the current it operates at.
To test to see if your transistors are functional, put that jig you are using away. Use you meter, starting with the diode test function.
-Chris
That doesn't bother me at all. Not knowing how you are getting your values is the problem.
You can find any number of things on the 'Net. It's up to you to sort out the rubbish from useful stuff. If the guy doesn't understand the importance of matching parts, he really doesn't know how amplifiers work. It's really as simple as that. So, yes his amp works, but it doesn't work "fine". It does function. That's the difference between knowledge and thrashing about with a partial clue.
So you are using the thing running off 15 VDC in the diagram, you are using a 9V battery? The battery is fine by the way. Please tell me precisely where you are measuring your voltages, give me the resistor value you are measuring across.
BTW, this setup will not really allow you to match transistors. You have no way to control the device temperature. The jig I posted cancels out the temperature issue and you are left measuring differential voltages. So it works by indicating a match at any reasonable temperature, and you can vary the current it operates at.
To test to see if your transistors are functional, put that jig you are using away. Use you meter, starting with the diode test function.
-Chris
Ok. Maybe I'm paranoid...
Just for the record, the jig I got I only used to check the 2N5087s for the diff pair. All other transistor/diode tests have been done with that BK meter I've got.
The way I measured the voltages for the 2N5087s was to measure the voltage across the base resistor (2k ohms) and to measure the voltage across the collector resistor (5k ohms). And yes, all of this was done with a 9V battery. It was with that thing that I got no voltage readings across the base resistor....
Like I said, probably cost me more time and money that I would have needed to spend....poop. That's what I get for being lazy...
I'll check the 2N5087s again later today. Going for a walk soon so I may not have those measurements until later tonight.
And again, you said to replace Q705, but where can I find a replacement?
Just for the record, the jig I got I only used to check the 2N5087s for the diff pair. All other transistor/diode tests have been done with that BK meter I've got.
The way I measured the voltages for the 2N5087s was to measure the voltage across the base resistor (2k ohms) and to measure the voltage across the collector resistor (5k ohms). And yes, all of this was done with a 9V battery. It was with that thing that I got no voltage readings across the base resistor....
Like I said, probably cost me more time and money that I would have needed to spend....poop. That's what I get for being lazy...
I'll check the 2N5087s again later today. Going for a walk soon so I may not have those measurements until later tonight.
And again, you said to replace Q705, but where can I find a replacement?
Hi Paco,
Okay, no problem. I also understand your problem.
Figure out how much emitter current there is. Divide that by your measured beta and multiply the result by 2,000.
How much voltage did you figure you should have?
What's the resolution of your meter?
Now you understand.
Okay, we see that your Q705 is a 40595 (from the schematic sheet). Using the all powerful Google search engine turned up the attached file. Your RCA 40595 turns out to be a 2N5322.
A real number, how about that!
-Chris
Okay, no problem. I also understand your problem.
Figure out how much emitter current there is. Divide that by your measured beta and multiply the result by 2,000.
How much voltage did you figure you should have?
What's the resolution of your meter?
Now you understand.
Okay, we see that your Q705 is a 40595 (from the schematic sheet). Using the all powerful Google search engine turned up the attached file. Your RCA 40595 turns out to be a 2N5322.
A real number, how about that!-Chris
Not wanting to leave you hanging here.
Here is the data sheet on your 2N5322 (attached).
We see that you will need this number, and it is still available, or a substitute. The ratings are:
PNP, 100 V C-E breakdown and 2 amperes collector current. The hFE is running between 30 and 130, it's a medium fast part.
You can use the same TO-39 case (TO-5 for us fossils), or move to a TO-220 and use a standard driver transistor. You will have to turn the part around to align the pins in that case. In the old days I would have reached for a 2SC2238, so whatever the new "nice drive" is would do. Note the 2238 was only good for 1.5 amperes, so a heavier one may be more prudent. An MJE15029 should work fine, even though it's a little slower (30 MHz vs 50 MHz). Those are easy to get.
-Chris
Here is the data sheet on your 2N5322 (attached).
We see that you will need this number, and it is still available, or a substitute. The ratings are:
PNP, 100 V C-E breakdown and 2 amperes collector current. The hFE is running between 30 and 130, it's a medium fast part.
You can use the same TO-39 case (TO-5 for us fossils), or move to a TO-220 and use a standard driver transistor. You will have to turn the part around to align the pins in that case. In the old days I would have reached for a 2SC2238, so whatever the new "nice drive" is would do. Note the 2238 was only good for 1.5 amperes, so a heavier one may be more prudent. An MJE15029 should work fine, even though it's a little slower (30 MHz vs 50 MHz). Those are easy to get.
-Chris
Here they are, I've not dealt with this company though, and I'd check as to who the manufacturer is. Hope they're not fakes:
http://store.americanmicrosemiconductor.com/2n5322.html?gclid=CK_YueiI25kCFcxL5QodvXGrUQ
The HK drivers have an integral heat sink, so you'll have to add one.
If you want to go MJE, I'd suggest the MJE15034 and complement - it has better hfe at lower currents where it is important for this design. Again add a small heat sink.
Pete B.
http://store.americanmicrosemiconductor.com/2n5322.html?gclid=CK_YueiI25kCFcxL5QodvXGrUQ
The HK drivers have an integral heat sink, so you'll have to add one.
If you want to go MJE, I'd suggest the MJE15034 and complement - it has better hfe at lower currents where it is important for this design. Again add a small heat sink.
Pete B.
Here's another, I've not dealt with this Quest Company:
http://www.questcomp.com/QuestDetailsAll.aspx?pn=2N5322&pnid=34097&stock=Yes
http://www.questcomp.com/QuestDetailsAll.aspx?pn=2N5322&pnid=34097&stock=Yes
Sorry I haven't given an update in such a long time, but I was finally able to check out at least something...
I checked all of the resistors before Q707, so that would be R713, R717, R719, R721, R705, and R707 if I read my schematic correctly and they're all fine now. The ones that were bad I've replaced.
I also diode tested Q709, not 705, and got essentially zero for all possible directions, which tells me that the thing is fried, but correct me if that's wrong.
Didn't test Q705. If I remember correctly, it should be OK, but I'll double check that later tonight.
Replacements for Q703 and Q707 will be ordered soon...
I checked all of the resistors before Q707, so that would be R713, R717, R719, R721, R705, and R707 if I read my schematic correctly and they're all fine now. The ones that were bad I've replaced.
I also diode tested Q709, not 705, and got essentially zero for all possible directions, which tells me that the thing is fried, but correct me if that's wrong.
Didn't test Q705. If I remember correctly, it should be OK, but I'll double check that later tonight.
Replacements for Q703 and Q707 will be ordered soon...
I also like Fluke meters Chris. Just wondering, I have a 45 here with a very, very dim display. There's no mention of this in the service manual, do you know if this was a common problem - any tips?
Just measured voltages on the display board, +5 is fine, but the negative voltages, -5.5, and -30V are zero.
Looking at the PSU schematics, I wonder if the filament shorted to ground.
Pete B.
Just measured voltages on the display board, +5 is fine, but the negative voltages, -5.5, and -30V are zero.
Looking at the PSU schematics, I wonder if the filament shorted to ground.
Pete B.
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