I should have added comma separators. Each colum is PIN number first and then voltage between pin 4 and the pin in each row.
Blast, sorry I am making mistakes. Hope you two can hang in there!!
Yesterday 5-8 is actually 8 to 5.
Yesterday 5-8 is actually 8 to 5.
I very much suspect your 0.01 Volt reading at R36, I think it should be 0.1 Volt.
I also think that THERE lies the source of your problem.
Connected to R36 should be a an Electrolytic Cap, but a short circuit in this cap presents a resistance of 640 Ohm, making it impossible for the output to raise pin 3 above 0.14 Volt.
So find the cap that is connected to R36 and you have probably solved your problem.
That C24 and R29 are in series is impossible, in that case there would not flow 0.13 mA current through R29 and R27, a current that also flows in R36 and the faulty cap.
And 0.13 mA x 640 Ohm is ca. the 0.1 Volt that I mentioned above.
As a matter of fact, C24 should read 104, meaning 100nF. This gives you the 3180 and 318 usec with R27 and R29.
Hans
I also think that THERE lies the source of your problem.
Connected to R36 should be a an Electrolytic Cap, but a short circuit in this cap presents a resistance of 640 Ohm, making it impossible for the output to raise pin 3 above 0.14 Volt.
So find the cap that is connected to R36 and you have probably solved your problem.
That C24 and R29 are in series is impossible, in that case there would not flow 0.13 mA current through R29 and R27, a current that also flows in R36 and the faulty cap.
And 0.13 mA x 640 Ohm is ca. the 0.1 Volt that I mentioned above.
As a matter of fact, C24 should read 104, meaning 100nF. This gives you the 3180 and 318 usec with R27 and R29.
Hans
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The one removed measures 330uf. Is that difference from spec significant?
When I test for continuity from R36 to the pads of the removed capacitor, the DMM only latches for a split second and then goes OL.. The same pad is connected to the RCA ground. Not sure I understand what is going on there. i’ll get into it in the morning.
When I test for continuity from R36 to the pads of the removed capacitor, the DMM only latches for a split second and then goes OL.. The same pad is connected to the RCA ground. Not sure I understand what is going on there. i’ll get into it in the morning.
As long as you measure 640 Ohm from R36 to GND, you haven't stil found the problem, are you sure you have the right Cap ?
330 uF for a 220 uF cap is fine, no problem.
When a multimeter first latches and then goes to OL, it means there is a Cap in between that gets charged by the measuring voltage of your DMM.
Hans
330 uF for a 220 uF cap is fine, no problem.
When a multimeter first latches and then goes to OL, it means there is a Cap in between that gets charged by the measuring voltage of your DMM.
Hans
As long as it takes
Lets see where the current line of investigation leads... if you don't find the issue then a new set of voltage readings ('cos I still can't make head or tail of the others
) would be great.
Gentlemen, we have won!
Before I describe what was faulty, I would like to buy you two an imagineray carton of beer in thanks for your support and patience (that is the Australian way). Your generosity in giving up your time to help overwhelms me. Forums like this are truely amazing places.
Even though this phono preamp was not worth much, I wouldn’t have paid anyone to fix it, it would have been almost as cheap to buy new (but thanks to the Ozzie member who offered early on).
In the end I had to remove a couple of film capacitors in order to trace the connection from pin 2 to ground but eventually located the suspected cap and replaced it with what I had in the same capacitance as you can see in the photo.
There was some small amount of brown residue at the base of the removed cap so maybe it leaked.
I quickly check some of the pin voltages on the opamps and they were different to those I reported yesterday, so quickly put it back together. Sorry I did not note the voltages.
I now have Dark Side Of The Moon coming out of both channels again.
This is probably my first significant non-trivial electronics repair success to date and I think I learnt plenty.
Thanks again Mooly and Hans.
Before I describe what was faulty, I would like to buy you two an imagineray carton of beer in thanks for your support and patience (that is the Australian way). Your generosity in giving up your time to help overwhelms me. Forums like this are truely amazing places.
Even though this phono preamp was not worth much, I wouldn’t have paid anyone to fix it, it would have been almost as cheap to buy new (but thanks to the Ozzie member who offered early on).
In the end I had to remove a couple of film capacitors in order to trace the connection from pin 2 to ground but eventually located the suspected cap and replaced it with what I had in the same capacitance as you can see in the photo.
There was some small amount of brown residue at the base of the removed cap so maybe it leaked.
I quickly check some of the pin voltages on the opamps and they were different to those I reported yesterday, so quickly put it back together. Sorry I did not note the voltages.
I now have Dark Side Of The Moon coming out of both channels again.
This is probably my first significant non-trivial electronics repair success to date and I think I learnt plenty.
Thanks again Mooly and Hans.
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and thanks for the kind words. It is always very satisfying to repair something... as you have found out.- Status
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