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Well at idle, you cannot take DC readings with signal banging around in an amp.
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Education is what you're left with after you have forgotten what you have learned. -
So look at that negative main rail. It reads substantially low. How much ripple is on it? Try this, set your meter to AC volts and read the good negative 50v rail. You should see after an initial bump, it should settle down to close to zero AC volts. Now do the same on the low positive rail. I'd wager you find it settles down to a considerable AC voltage. WHich would mean the filter cap is not working. And that most likely do to broken solder or crack in the copper traces.
Or best way: scope it.Education is what you're left with after you have forgotten what you have learned.Comment
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Clipping on the collectors of Q2 and Q12, both measure 9v AC ripple. Scope shows same waveform on both.Comment
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Found it and kind of pissed at myself for missing this. Notice the broken trace? Tunnel vision is a bitch. Don't worry I touched up that diode joint as well.Comment
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Burnt right out. I was about to respond that 9vAC sounded really high for ripple, even if same side to side. And indeed I was thinking an open ground. The 10v high on the -52 rail should have been a clue but I missed it.
Glad you found it. Generally these old PV boards are a snap to service.
Once it is working, just for grins, slap that 87478 back in and see if it now works too. It might have been reacting to the odd supplies. If it is indeed bad, well, run without it if we must.Education is what you're left with after you have forgotten what you have learned.Comment
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Agreed these are not overly complicated hence why I was banging my head against the wall. I put that 87478 back in first thing and it seems to be working, although I haven't tried bringing in the compression light yet. I had subbed in 50v filters for testing, so I need to order the right caps and then send it on its way.Comment
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THose old 5000uf 55v caps are long ago history, 4700uf at 63v is the closest standard value.Education is what you're left with after you have forgotten what you have learned.Comment
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That's what I was looking at. I actually have some 4700/55's but they are axials. I plan on spending the $15 and doing it right.Last edited by tdlunsfo; 07-24-2022, 10:07 PM.Comment
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Just to let you know, the pin spacing won't fit, you'll need to drill a hole or two. Careful there.Education is what you're left with after you have forgotten what you have learned.Comment
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