Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: thoven0215 on May 28, 2022, 03:30:34 AM
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I just put in my shunt regulator upgrade, and there seems to be hum in the right channel. The voltages at OA and OB are both near 380 instead of 300-305, and KregB is at 10 instead of 2.5-5. What could be the issue?
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We definitely don't recommend listening to an amp that doesn't pass its voltage checks.
Do you have the +Reg to Breg jumpers installed? If so, can you post some build photos?
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I didn't at the time. I installed them and measured, and now OA is near 375, OB is 300-299, and Kreg is now floating between 1 and 2.
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There's a Kreg on the A side and a Kreg on the B side. It's unlikely that they are both between 1-2V when one of your regulators appears to be working and the other isn't. Can you post the actual voltages for Kreg A and Kreg B?
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Oops I omitted the B. Kreg A is at 5 Volts and Kreg B is at 1-2 Volts.
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There's a 50/50 chance that if you replace the 431 regulator on the low side, everything will snap back into place and work properly.
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I do not have an extra regulator to replace it. Should I contact the replacement parts email?
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Yes.
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I replaced the regulator, but the problem still persists. All the values still measure the same as I last stated. What do I do next?
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What voltage do you see a KregB? If it's still well below 2.5V, I'd want to see the bottom of the C4S/Regulator PC board.
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Sorry for the late reply, I had a nasty case of the flu. I rechecked the back of the board and noticed I did solder a wire to the wrong spot. I fixed it and here are some pictures of the back and front. Is there anything I've missed?
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I would give it another shot. Do you remember which connection wasn't where it was supposed to be?
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Yes, I put it in the hole above OB (when you orient the letters correctly). I tried soldering everything back in and testing the voltages, but it started smoking. I unplugged and saw that it seemed to be the resistor next to the capacitor on the B side of the board that was smoking. It appears cracked now. What should I do?
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I can't seem to post the images, so I will keep trying until I figure it out
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Pics
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Other pics
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Does the 2.49K resistor still measure 2.49K?
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My apologizes for the late response, came back from a trip and had a case of covid. The 2.49 resistor measures at around 0.08 now.
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I would start by replacing that part and the TL431 on that side as well.
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Did you mean the LM431 regulator? I looked at the parts list for the shunt regulator and only saw the LM431 and no TL431.
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Yes, they are the same part from different manufacturers.
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I just want to confirm that my JC2907AN43 is the same as the PN2907A transistor.
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Correct.
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As I was analyzing the B tube socket, I noticed B5 was making contact with B6. Could that have been causing the issue?
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That will definitely cause some major issues.
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Finally got around to replacing the resistor and regulator and putting the board back in place. Should I go ahead to the voltage check? Here are some pictures of around the board.
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On the piece of STP in your photo, there's a lot of extra foil hanging around. If that foil comes into contact with anything other than the chassis, you can run into some real issues. Other than that, yes, you will need to do some voltage measurements.
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After cleaning up the foil I measured and found all normal values for IA, OA, KregA, but for IB, OB, and KregB, I got 0 volts dc. I noticed the LEDs on the B side of the board didn't turn on, and the A side of the small pcb also didn't light up.
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IB is fed from a high voltage node in the power supply. If that node is pulled to 0V, you will burn up resistors pretty much immediately and you'll know there's a problem. Since you haven't reported that this happened, you either do not have IB connected to the correct spot, or that wire is broken.
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I checked and my connections seem to be correct. I checked both the IB on the small pcb and the shunt regulator board. I have IB on the small pcb connected to 12L and the IB on the shunt regulator at 34U. I measured the resistors around my shunt regulator board, and some of them do not measure as expected. The 300K ohm 3W resistor on the A side measures at around 200k on the A side. The 330k ohm 2 Watt resistor measures at 0 on the B side. The 64.9 ohm 1/8 watt resistor measures at around 12 ohms on the B side.
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OK, in your previous post you mentioned IB, OB, and KReg being 0V. This is on the larger C4S board, not the smaller one (it doesn't have a Kreg).
IB on the larger PC board wires into the high voltage power supply at 34U, and you need to do a DC voltage check of 34U. If it's 0V that is significant. If it's more like 380V and IB is 0V, then they are not connected.