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.
Repair service [resolved]
- Thread starter preston.ezell
- Start date
preston.ezell
New member
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.
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
New member
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
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
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
New member
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.
preston.ezell
New member
And @AB2KH as a direct response to what you were suggesting, I measured and I have around 207V at the point where the B+ connects to the small board. I have around 75V where the board connects to the AU7 plate from terminal 5. I have 0V where the board connects to the AU7 plate from terminal 1.
So perhaps this will come down to a replacement of the small board.
So perhaps this will come down to a replacement of the small board.
You can e-mail queen(at)bottlehead(dot)com to request a repair box. Be sure to paste a link to this thread so she knows you've been here.
-PB
-PB
preston.ezell
New member
Last time I did this check both were glowing, but I will check again after work and report.
My thinking in my previous post is not sound so please disregard it.
You have supply voltage but no output voltage and the LED's are not lit and they should be on regardless of wether there is a plate load present or not. So that would confirm that there is/are components that are "tutafineut". PB is correct, the best/easy answer is go for a new board and parts.
I would be curious as to the final results so keep us posted.
Chris/AB2KH
You have supply voltage but no output voltage and the LED's are not lit and they should be on regardless of wether there is a plate load present or not. So that would confirm that there is/are components that are "tutafineut". PB is correct, the best/easy answer is go for a new board and parts.
I would be curious as to the final results so keep us posted.
Chris/AB2KH
preston.ezell
New member
So, although they might be dim (I’m not sure of what brightness level would be considered normal) both sides are lit.
https://drive.google.com/file/d/1a00w5hmAVk5NLZ5j4J2NKWaBUBzQ7H_H/view?usp=drivesdk
https://drive.google.com/file/d/1a00w5hmAVk5NLZ5j4J2NKWaBUBzQ7H_H/view?usp=drivesdk
preston.ezell
New member
I’m sorry if this is a dumb question, but again I’ve never done this sort of thing before.
What is the LES?
What is the LES?
preston.ezell
New member
Did you mean LEDs?
Paul Joppa
Moderator
I think AB2KH meant LEDs, and I suggest not touching them up yet - they are so small they can easily be overheated.
I got this repair on the bench today, and the PN2907 did not survive being installed backwards and was shorted out, and this pretty much tanked that half of the small PC board up front. One LED on the 9 pin socket was open also. The LED problem and some other soldering related issues look to be from using an iron that's not hot enough to properly flow out the solder quickly.
Fixing up the front PC board, I was then left with one dead channel and one half of your rear PC board that just wasn't passing any current. When I unscrewed your rear board and moved it, all of the wires broke in a way that's consistent with using a wire stripper on too small of a setting, which will cut into the solid core wire and weaken it so it snaps off. When I went to work replacing these, I discovered that all of the wire ends going to the terminal strips were just resting on the terminal strips with some solder, not passing through the terminal strip holes themselves, so I had to replace every wire required for Speedball installation because connections like those are likely to pop loose later on their own.
After installing all of the new wires, there was also some distortion in the previously working channel which I tracked down to a damaged transistor on the other side of the large PC board.
With all of those issues addressed, this amp is now up and running.
Fixing up the front PC board, I was then left with one dead channel and one half of your rear PC board that just wasn't passing any current. When I unscrewed your rear board and moved it, all of the wires broke in a way that's consistent with using a wire stripper on too small of a setting, which will cut into the solid core wire and weaken it so it snaps off. When I went to work replacing these, I discovered that all of the wire ends going to the terminal strips were just resting on the terminal strips with some solder, not passing through the terminal strip holes themselves, so I had to replace every wire required for Speedball installation because connections like those are likely to pop loose later on their own.
After installing all of the new wires, there was also some distortion in the previously working channel which I tracked down to a damaged transistor on the other side of the large PC board.
With all of those issues addressed, this amp is now up and running.
Hope you had some good coffee beforehand!
I split the work between two different days, so that helped a lot!
