Thomas Vox Cambridge Reverb V1031 - mystery voltages?

[MWaldorf]

With the help of the great folks on this forum, I was able to revive a V1032 last year, and now I'm giving a V1031 a refreshing. I've replaced all the electrolytic caps, tested all the other caps and the resistors and replaced a few that were out of spec. Fired it up, sounded fine, but no reverb. Got out my multimeter and started poking around. I've got 31V at the main filter cap, but my 27V source reads 16.8V and my 17V source reads 11.4V. I rechecked everything and even replaced all the transistors on the board (using 2N2219As for Q4 and Q7 and 2SC1815s for the rest. Still getting the same readings. I've checked for shorts and I can't find any.

The amp had correct voltages before I took it apart, which would seem to suggest I botched something, though I don't know where. Does anyone have any suggestions for next steps of troubleshooting?

Thanks, Mel

Here's the schematic for the V1032; same amp without the E-tuner.
V1032-Schematic

[g1]

If the 27V node of the supply is low, then the 17V node will also be low.
Does R53 check out at 100 ohms? R54 at 680 ohms?

[MWaldorf]

If the 27V node of the supply is low, then the 17V node will also be low.
Does R53 check out at 100 ohms? R54 at 680 ohms?

Ugh, ok, I found the problem - ME. I'm leaving it here for posterity's sake as a warning to the next schmuck. So, I printed out the circuit board layout to use when measuring component values. I knew I needed to replace Q3 and Q4, and to make things easier for myself (HAHAHA!!!) I marked the base, emitter and collector on the layout diagram - B,E,C, nice and simple to follow when I'm soldering, right?. Then, drum roll please, I WROTE THE WRONG LETTERS!!! Yup, I wrote B where I should have written C and C where I should have written B. I didn't notice this while troubleshooting because once I put the heat sink on I couldn't see the transistor pinout anymore, and assumed I must have done it right when I soldered it in. The odd thing is I remember thinking it was strange to have to twist around the pins to fit the PCB, but figured, oh well, Thomas Vox did strange things. Then I should have noticed it when I installed Q7, the same type of transistor, and didn't have to do the strange twisting. Swapped in a new transistor, this time with the proper pin placement, and boom the amp is back.

Now the amp is rip roaring like the nasty little rock and roller it's supposed to be.

The moral of the story is - when troubleshooting, START AT THE FIRST STEP. If I'd gone back through and reviewed my board layout diagram I would have seen the error yesterday.

The second moral of the story is - if you've had a concussion within the last year, you may think you're firing on all cylinders, but there's a chance you're not!

Anyway, thanks G1!