Yes, they are the same part from different manufacturers.
Right Channel Hum [resolved]
- Thread starter thoven0215
- Start date
thoven0215
Member
I just want to confirm that my JC2907AN43 is the same as the PN2907A transistor.
Correct.
thoven0215
Member
As I was analyzing the B tube socket, I noticed B5 was making contact with B6. Could that have been causing the issue?
That will definitely cause some major issues.
thoven0215
Member
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.
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.
thoven0215
Member
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.
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.
thoven0215
Member
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.
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.
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.
thoven0215
Member
Apologies for the 3 year response time. I was finishing up school. After re-reading the thread and re-checking the voltages, IB and OB are at around 0.9 volts. KReg on the B side is about 0.9 volts. 34U is also at 0.9 volts. I may have not checked the lower voltage settings on my multimeter at the previous time. You said that
and on reply 12 I stated that the resistor next to the capacitor on the B side started to smoke as I checked the voltages. Could this be what you are talking about? I also used my continuity checker on my multimeter and it says that 34U and IB are connected. Thanks for your help as always.Paul Birkeland said:
Can you post some photos of what you're seeing?
thoven0215
Member
Please let me know if more pictures are needed. One of the pictures is with the amplifier powered on in order to see the LEDs. The other two are with the amplifier off.
Which resistor? Which terminals does it connect to and what's its value?thoven0215 said:
thoven0215
Member
It was the 2.49k ohm 1/4 W resistor that goes into R3 on the big circuit board. I replaced it after that smoking happened along with the TL431 and the resistor measures at about 2.39k ohms right now.
I think what would make sense is to put the amp back to pre-shunt regulator status and just be sure everything still works under those conditions.
thoven0215
Member
I put the amp back into pre-shunt regulator conditions, and the issue of 34U being 1.8 volts still persists.
With the amp powered down and the high voltage bled off, you should be able to measure the resistor that goes to terminal 34 while it is installed in the amp, I'd imagine it will measure as infinite resistance and needs to be replaced.
thoven0215
Member
You are speaking about the 130 ohm 2W metal film resistor correct? It does appear as infinite resistance. Can you please remind me what the email is to order spare parts? Thank you.
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