and finally this is Q13 collector
and Q14 collector is the same or has same waveform.
the Q12 base is nothing (zero amplitude)
i think that covers them all, at least the first couple transistors.
so again the problem is that the output is not a sine wave, its morelike Q11 collector look. and the meter circuit isnt functioning (i think because the output is wrong. ill get to the meter after the balanced amp is fixed)
hopefully that will give you a more 'in the lab' or 'on thebench' feel for diagnosing this oscillator. Im not sure about the negative feedback, but I did check all the DC values, and most were in tolerance, but some were out, I would have to go back and see.
The one other problem is that I dont have that great of a DMM and i am not sure what the internal resistance of it is. its pretty cheap.
Im gonna get a fluke 117 or 87 soon ( which would you prefer?)
thanks again my fellow diyers!
I will start doing all the fun circuits once this thing is fixed. onwards with diy!
and Q14 collector is the same or has same waveform.
the Q12 base is nothing (zero amplitude)
i think that covers them all, at least the first couple transistors.
so again the problem is that the output is not a sine wave, its morelike Q11 collector look. and the meter circuit isnt functioning (i think because the output is wrong. ill get to the meter after the balanced amp is fixed)
hopefully that will give you a more 'in the lab' or 'on thebench' feel for diagnosing this oscillator. Im not sure about the negative feedback, but I did check all the DC values, and most were in tolerance, but some were out, I would have to go back and see.
The one other problem is that I dont have that great of a DMM and i am not sure what the internal resistance of it is. its pretty cheap.
Im gonna get a fluke 117 or 87 soon ( which would you prefer?)
thanks again my fellow diyers!
I will start doing all the fun circuits once this thing is fixed. onwards with diy!
Attachments
OK, a quick look would indicate :
Q11 is OK. The funny looking collector signal is due to it emitter shifting (as its part of a diff amp)
Q12 is OK. There is a collector signal - it looks wierd since its base is clamped (the fault condition - it should look like Q11's base) and its emitter is shifting due to signal in Q11.
All in all, the diff pair Q11/12 are working the best they can but they are running out of 'swing' since there is no feedback
I'll have another look later ...
Q11 is OK. The funny looking collector signal is due to it emitter shifting (as its part of a diff amp)
Q12 is OK. There is a collector signal - it looks wierd since its base is clamped (the fault condition - it should look like Q11's base) and its emitter is shifting due to signal in Q11.
All in all, the diff pair Q11/12 are working the best they can but they are running out of 'swing' since there is no feedback
I'll have another look later ...
A couple of analysis tips:
(1) for diff amps, look at both collector signals at the same time, dc coupled and the same gain. They should be 'roughly' in anti-phase (mirror image) whatever the input signal is if the amp is operating normally. A caveat is that when the diff pair is biased with a resistor (like in this example) the bias point will move around somewhat with any common mode input. In the case of Q11/12 the amp is operating outside its normal range but doing its best ...
(2) for an individual transistor, look at the base and emitter signals at the same time, dc coupled and the same gain (set the traces to be co-incident before connecting the signals). They should look near identical with something like 0.5 to 1 volt between them if the transistor is in its normal operating condition.
My 1st stab at the fault would be Q21 (since its the OP and will be the first to suffer in a fault condition) as there is no feedback at Q12's base ...
(1) for diff amps, look at both collector signals at the same time, dc coupled and the same gain. They should be 'roughly' in anti-phase (mirror image) whatever the input signal is if the amp is operating normally. A caveat is that when the diff pair is biased with a resistor (like in this example) the bias point will move around somewhat with any common mode input. In the case of Q11/12 the amp is operating outside its normal range but doing its best ...
(2) for an individual transistor, look at the base and emitter signals at the same time, dc coupled and the same gain (set the traces to be co-incident before connecting the signals). They should look near identical with something like 0.5 to 1 volt between them if the transistor is in its normal operating condition.
My 1st stab at the fault would be Q21 (since its the OP and will be the first to suffer in a fault condition) as there is no feedback at Q12's base ...
that's funny I immediately diagnosed Q11 as the faulty transistor!however, upon reading your explanation, what you are saying makes sense, especially since our friend deyjavont here said the DC voltages seemed good.
but what about the DC voltages in the output section?
Deyjavont, are the collector voltages of Q18 and Q20 correct, as well as Q19 and Q21? If so then the easiest next step to do is verify the feedback resistors, following DRC's trail. these resistors, R51 and R53, should measure their value, within 5%, I am guessing. this is without removing the caps in parallel with them, because their impedance should not not shunt that 2K resistor value.
now if those are OK, check R74 and R75, they also are in the feedback path. Still if that checks out, well, you could do two things:
-Replace q21 as DRC would probably suggest,
-disconnect the amp from the attenuator switch. It is possible that something has shorted out in the switch assembly, on one of the sides (remember this has two identical switch networks, it's positive half on one and negative half on the other). Then see if the problem is still there.
ah, my rambling is done.
Hey, it takes time to explain correctly!
How were those tests deyjavont?
but what about the DC voltages in the output section?
Deyjavont, are the collector voltages of Q18 and Q20 correct, as well as Q19 and Q21? If so then the easiest next step to do is verify the feedback resistors, following DRC's trail. these resistors, R51 and R53, should measure their value, within 5%, I am guessing. this is without removing the caps in parallel with them, because their impedance should not not shunt that 2K resistor value.
now if those are OK, check R74 and R75, they also are in the feedback path. Still if that checks out, well, you could do two things:
-Replace q21 as DRC would probably suggest,
-disconnect the amp from the attenuator switch. It is possible that something has shorted out in the switch assembly, on one of the sides (remember this has two identical switch networks, it's positive half on one and negative half on the other). Then see if the problem is still there.
ah, my rambling is done.
Hey, it takes time to explain correctly!
How were those tests deyjavont?
Okay, wow, it has been a long time since I posted any information about the 654A!
I am pretty sure I pinned it down. It is the optoisolator used for controlling the input to Q8 of the buffer amplifier.
The problem is now, where do I find one of these? The case of it says VACTEC 8063 and of course one side is a light-sesitive resistor, and the other side is a lamp, both encapsulated in the same package.
So yes...perhaps someone here has some experience with this (it is an HP 654A Sine Wave Oscillator.)
I'll post a picture of it soon.
When I applied a resistance of 500 ohm where light sensitive resistor is, the waveform almost cleaned right up..if that is any help.
Thanks alot guys!
I am pretty sure I pinned it down. It is the optoisolator used for controlling the input to Q8 of the buffer amplifier.
The problem is now, where do I find one of these? The case of it says VACTEC 8063 and of course one side is a light-sesitive resistor, and the other side is a lamp, both encapsulated in the same package.
So yes...perhaps someone here has some experience with this (it is an HP 654A Sine Wave Oscillator.)
I'll post a picture of it soon.
When I applied a resistance of 500 ohm where light sensitive resistor is, the waveform almost cleaned right up..if that is any help.
Thanks alot guys!
Hey deyjavont,
you finally got to it! I was going to talk about this in my email but I forgot. anyway, you might check good old ebay for vactrol spares, or I might know a few places that might replacements, but check here on diyaudio, you're bound to find at least one post that asks about these. I believe they were used in many compressors and limiting amplifiers, like the ones from Universal audio and maybe fairchild. but I'm not even 90% sure.
I like your avatar!
Hey Chris what do you have as far as open reel decks go? I am looking for the reel tables (spindles)
you finally got to it! I was going to talk about this in my email but I forgot. anyway, you might check good old ebay for vactrol spares, or I might know a few places that might replacements, but check here on diyaudio, you're bound to find at least one post that asks about these. I believe they were used in many compressors and limiting amplifiers, like the ones from Universal audio and maybe fairchild. but I'm not even 90% sure.
I like your avatar!
Hey Chris what do you have as far as open reel decks go? I am looking for the reel tables (spindles)
Yea, the avatar is me on Alcatraz with San Fran in the background. What a fun trip.
As reel to reels go..I only have two with me here in Burnaby, and they are pretty low quality consumer grade. ( I think made by Archer??) But they are a pair, so I wanted to use them both for whatever I wanted (the first idea was doing a Robert Fripp style Frippertronics with the two looped together, but they didnt work, so now one is still assembled, and the other is disected for tube parts) but yes, if you would like parts off of it, Ill send yo some pictures and what not of them!
Tonight I am going to test to see how much current was/is passing through the light bulb to find the reason why it failed (maybe because it is almost 50 years old??)
As reel to reels go..I only have two with me here in Burnaby, and they are pretty low quality consumer grade. ( I think made by Archer??) But they are a pair, so I wanted to use them both for whatever I wanted (the first idea was doing a Robert Fripp style Frippertronics with the two looped together, but they didnt work, so now one is still assembled, and the other is disected for tube parts) but yes, if you would like parts off of it, Ill send yo some pictures and what not of them!
Tonight I am going to test to see how much current was/is passing through the light bulb to find the reason why it failed (maybe because it is almost 50 years old??)
Well, then I shall pass on the reel to reel deck devices. If you have a particular project for them, I will not break a pair, because I can really use any deck to get parts. My thing is "cannibalizing" discarded equipment, stuff that's too far gone to be restored, and using it to make something similar, just because I can. Or I think I can..
Anyhow, take a look at page 6-3 of the service manual of your 654a. Look at reference designator DSV1, the manufacturer's part number is CLM5012. I found nothing on the net for this part. I dd however find CLM6000, but that tells us nothing about the 5012. If one can ssume they are closely related, then the specs of the CLM6000 could be the same for the CLM5012. anyway, I'm still wondering how you can determine a good replacement for this. If only someone had a Vactrol (I think they became clairex) catalog, we would have some specs...
euh, help, anyone?
tu parles d'un nom "vactrol"... Pas ben ben de québécois su'l site hein!? non hein.. pas un qui lis ça hein sinon i pourrait peut-être nous donner un signe de vie?
Anyhow, take a look at page 6-3 of the service manual of your 654a. Look at reference designator DSV1, the manufacturer's part number is CLM5012. I found nothing on the net for this part. I dd however find CLM6000, but that tells us nothing about the 5012. If one can ssume they are closely related, then the specs of the CLM6000 could be the same for the CLM5012. anyway, I'm still wondering how you can determine a good replacement for this. If only someone had a Vactrol (I think they became clairex) catalog, we would have some specs...
euh, help, anyone?
tu parles d'un nom "vactrol"... Pas ben ben de québécois su'l site hein!? non hein.. pas un qui lis ça hein sinon i pourrait peut-être nous donner un signe de vie?
Oh, dont pass on the reel to reels!! All I would be doing with them right now is scavenging the trannys and tubes and what not, but all the mechanical is just sitting there. I do have better ones, but they are all in Alberta with my parents.
Back to the optoisolator...I cant disect this one to find out if its a LDR and LED, or if it is actually a lamp (the difference being that LED only conducts (for majority carriers) in one direction.
Looking at the schematic I think if it IS an LED/LDR I could hook the cathode end to circuit common, and anode to the rest of the ampltude control integrator.
Ill try to bias the device I removed (if its able to..cant test it without it being on. haha. ) and see whats what, but I think it is a lamp with a burned filament.
I couldnt find any info on the VACTEC 8603, but I did find that small bear electronics sells the Clairex CLM6000 (what you mentioned) for 7.95 (ouch) but yes, like you said..all the phasor guys still use these, so I should be able to find one
Then thats the next question..how much is this device allowed to deviate and still work in the circuit?? I measured 500 ohms (about) for the sinewave to clear up, and these are 500ohm Ron, so possibly just plop one in and see I guess
I have a Roland Phase 5 (guitar pedal) and I do recall it having an optoisolator like this one..Ill open it up and see. They are almost the same vintage. haha
Also, the effect makers rave about.. VTL5C3, and...NSL32 but I havent researched them yet.
Gotta love/hate HP and thier resistive-lamp-feedback circuits!! haha
Back to the optoisolator...I cant disect this one to find out if its a LDR and LED, or if it is actually a lamp (the difference being that LED only conducts (for majority carriers) in one direction.
Looking at the schematic I think if it IS an LED/LDR I could hook the cathode end to circuit common, and anode to the rest of the ampltude control integrator.
Ill try to bias the device I removed (if its able to..cant test it without it being on. haha. ) and see whats what, but I think it is a lamp with a burned filament.
I couldnt find any info on the VACTEC 8603, but I did find that small bear electronics sells the Clairex CLM6000 (what you mentioned) for 7.95 (ouch) but yes, like you said..all the phasor guys still use these, so I should be able to find one
Then thats the next question..how much is this device allowed to deviate and still work in the circuit?? I measured 500 ohms (about) for the sinewave to clear up, and these are 500ohm Ron, so possibly just plop one in and see I guess
I have a Roland Phase 5 (guitar pedal) and I do recall it having an optoisolator like this one..Ill open it up and see. They are almost the same vintage. haha
Also, the effect makers rave about.. VTL5C3, and...NSL32 but I havent researched them yet.
Gotta love/hate HP and thier resistive-lamp-feedback circuits!! haha
Well, I don't need the parts right away to be honest, like I said I got the "other" big project to finish first!
you know instead of putting a fixed 500 ohm resistor, why don't you just put in a linear 2Kohm variable resistor? Or somewhere around 2K, close enough to 500 ohms but will give you enough room upwards to clear it up. I don't get the impression that this particular optocoupler goes to very high resistance. Personnally I think this was a custom-made part for HP. Have you tried sphere electronics in BC? ( http://www.sphere.bc.ca/ ) Maybe they have a spare part for this, altough, you're likely to pay a high price, but if they have it it will be the exact part from HP.
Your idea of dissecting the optoresistor is good, that's what I would do. I am certain it's an incandescent lightbulb in there, and it's burnt. If you can find "wheat-germ" light bulb, in either a hobby store, or any electronics store, you might be able to make a drop-in replacement! That would be super. But you have to able to open up the case in a way that permits reassembly you know... lol!
good luck, or good work!
you know instead of putting a fixed 500 ohm resistor, why don't you just put in a linear 2Kohm variable resistor? Or somewhere around 2K, close enough to 500 ohms but will give you enough room upwards to clear it up. I don't get the impression that this particular optocoupler goes to very high resistance. Personnally I think this was a custom-made part for HP. Have you tried sphere electronics in BC? ( http://www.sphere.bc.ca/ ) Maybe they have a spare part for this, altough, you're likely to pay a high price, but if they have it it will be the exact part from HP.
Your idea of dissecting the optoresistor is good, that's what I would do. I am certain it's an incandescent lightbulb in there, and it's burnt. If you can find "wheat-germ" light bulb, in either a hobby store, or any electronics store, you might be able to make a drop-in replacement! That would be super. But you have to able to open up the case in a way that permits reassembly you know... lol!
good luck, or good work!
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