Repair service [resolved]

[preston.ezell]

This is with the 6080 unplugged, btw

[Paul Birkeland]

How about the same measurement on terminal 5?

[preston.ezell]

https://drive.google.com/file/d/13Cy4hq923tAkbmj7nLxxVBiKpKtCFmKy/view?usp=drivesdk

0L

[AB2KH]

Is it possible the junction of the 2907 was damaged ?

Chris/AB2KH

[preston.ezell]

https://drive.google.com/file/d/1qTdLVCjuhDLUKdV2IXVHmoLY5ynbcnas/view?usp=drivesdk

2907

I did have to de-solder and flip this transistor.

There is a small voltage going through my A side 2907 and about 100+k ohms of resistance

[preston.ezell]

I have a -0.4V at A7. My led there is also not lit. It was before the speedball

[AB2KH]

Not to confuse the issue with facts, Your reply post #28 and #32 photos IMG4686 & IMG4687 Indicate that your amp is ON and your meter (looks like) it is set to ohms/resistance. If infact you are looking for a resistance reading the amp should not be ON. On the other hand if you are trying measure voltage then your meter is not set to the correct position.

Chris/AB2KH

[preston.ezell]

https://drive.google.com/file/d/1s3cg-cC4pEu_gMxkMnfLHigXYracccgp/view?usp=drivesdk

https://drive.google.com/file/d/1PhDFCLMSEH-wQ5ZMHsJ-1Zj5lHr8hk5l/view?usp=drivesdk

Sorry, you are correct! I accidentally had the amp on during my resistance measurement.

Here are the correct/proper readings.

[AB2KH]

PB is the expert here! and I agree you should focus on the small board at this point.

My amp has the old style boards so the connection identifiers are most likely different but the circuit I believe is the same. So hopefully you can follow by following the schematic.

The point at which the B+ connects to the the small board should be somewhere around 170 VDC (at least on my schematic) now if you measure the point at which the board connects to the plate of the 12AU7 you should see about 75VDC (at least on my schematic). You should be able to confirm these voltages from the working side of the board.

If you don't have 170 VDC on the in put you have a power supply issue.

If you don't have close to 75VDC on the plate of the 12AU7 then there is / are faulty components on that side of the board or a grounding issue between the cathode and ground. You did say it was working before speedball so that most likely is not a problem.

My money is on the 2907 being damaged either from incorrect installation initially or from heat damage during extraction and re insertion.

I hope this helps

PB you have the floor.

Chris/AB2KH

[preston.ezell]

I am a bit concerned that I damaged the 2907 from the de and re soldering I did.

The legs got pretty hot in order to extract it. Is there anyway I can test directly whether or not that transistor is damaged?

I’m at work right now, but when I get home I can check these values and see if they’re around what’s expected.

This is my very first experience with any of this stuff, so I’m learning quite a bit all at once. It’s both exciting and frustrating.

I’ll let you know what I find tonight after work.

[Paul Birkeland]

You could certainly try replacing the PN2907.  You could also contact replacementparts(At)bottlehead(dot)com and ask for a new small board and small board parts.

[preston.ezell]

I will go ahead and get the small board replacement and go from there, I suppose.

lol I almost wish I hadn’t heard it before I goofed. That way I wouldn’t have known how it sounded before losing it.

[preston.ezell]

So I've made an observation.  The middle leg of my A side MJE350 has no voltage.  You can see this in the photos below.  I tested the three legs of each MJE350 and noticed that only the middle leg of the A side does not give a voltage reading.  I thought that this perhaps may be due to a problem with the transistor, so I switched the A and B side, and still am not getting a reading from the middle leg.  Earlier it was proposed that the 2907 was damaged from the resoldering, but I have checked all of the legs for the resoldered 2907, and they all have a voltage reading.

I'm not sure if this really means anything, as I don't have any prior experience with circuits like this, but it feels like to me that these readings mean that there isn't really a problem with the small board, and it seems the 0V reading at terminal 1 is due to something somewhere else in the circuit.

So, IDK.  Let me know what you think.

https://drive.google.com/drive/folders/1zyGib1GURGJ0z39O52nla8TNa_0DoxiH?usp=sharing

-preston

[Paul Birkeland]

The 0V reading would be consistent with a short dragging down the output of the C4S board.  You might check the wire going from terminal 1 to B1.  If the insulation is melted and it's touching B8, that would cause this problem.  It looks quite a bit longer than what it needs to be, so it's hard to tell what it might be touching or if it perhaps got touched with a hot soldering iron somewhere along its length and is making contact where it shouldn't.

[preston.ezell]

I just went over the entire circuit and quadruple checked to make sure there are no connections being made where they are not intended to be made. I have no idea anymore. Sad day.