Need help, V2 silent after mods to lower board

[ehx]

First post here, and I'm in need of some trouble shooting help .

Having stumbled upon this forum I dug out my old V2 which had been sitting on a shelf for the last five years.

I built a new PSU for it (always hated the stock wall wart) - it worked great.

Then I swapped the valves for a pair of 6N23P - Nice!

Still no problems.

Then I swapped all the capacitors on the upper board for 1500uF FCs, replaced all the diodes and did the gain adjustment mod on the lower board - no problems, the amp worked perfectly after this too.

So, tonight I opened it up again and did the "usual" mods to the lower board. (I know, I should have done one thing at a time, testing betwen each... but I got a bit too confident):
Replaced the plastic valve sockets with ceramic ones
Replaced all electrolyte caps with {4x100uF FCs, 2x470uF non-polar and 2x10uF non-polar}
Replaced the phone jack
Replaced the volume pot

Now when connect and turn on the PSU, the LED lights up, but that's about it.
No sound from the headphones.

I've taken the boards out of the casing and powered it up - the valves don't light up (they should, right?).

I've inspected all the joints for bad soldering or shorts, but can't find anything that looks too bad (It's not the first time that I've used a soldering iron).

I haven't got a lot of testing equipment, only a decent digital multimeter.

Can someone please help me with tips on how I should proceed with trouble shooting this?

Any tips/suggestions/ideas would be highly appreciated!

Thanks,

/Erik

[PinkFloyd]

First off check you have fitted the 100uF caps the right way round.....

[ehx]

Thanks,

Checked: "gold band" on the side of the 100uF FC caps is opposite to "+" markings on PCB. So they should be correctly positioned...

Any voltages I should/could check to see where the problem might be?

[ehx]

All I'got on hand is a crap camera phone, so... not sure if the photos are of any use.

Upper board




Lower board

[Deleted]

ehx
It may be time to get out your Digital meter, and check that you have filament voltage for the tubes, which in the absence of a schematic, I would assume have their filaments connected in series ,and working from a 12V supply ? You should also have supplies of +24V and -21V available from the main supply.

Sandyk

[leo]

Yep, sounds like theres a voltage missing somewhere, you have the fun of trying to trace it, it may take some time but with some patience you should find it, could be anything from a hairline crack in the pcb print to something like an open circuit resistor, also check solder joints, check for any shorts

BTW it only takes a tiny short to cause problems

Is there a V2 schematic available to view? if so we could maybe give a few idea's where to check

[Deleted]

Leo
I have a copy of a "reverse engineered" V2 schematic, but it does not show the PSU area.Only shows +24 and -21V supply rails.
Neither does it show filament connections.
Alex

[leo]

Alex,

Thats a pity, it was just an idea, as you know the proper schematics have the component numbers marked on (R? , TR? etc) making it easier to suggest what area's and components to measure at.

Leo

[ehx]

All, thanks for the tips so far!

I got the multimeter out and did some measurements.

PSU output: 14 V (AC)

Top board connector (disconnected from lower pcb):
Pin | Voltage (DC, used outer ring on PSU connector as ground ref)
1 | 0 V
2 | 38.5 V
3 | 0 V
4 | 0 V
5 | -38.2 V
6 | 0 V

I got the same numbers (except for 0.7 V drop on pin 5) when I did the same measurement with the top board connected to the lower board.

Lower board

VCC (at R110): 38.4 V
VNEG (at R112) -37.1 V


Valve sockets (very similar measurements on V101, V201):
Pin | Voltage (DC)
1 | 37 V
2 | 0 V
3 | -36.8 V
4 | 0 V
5 | 0 V
6 | 37.8 V
7 | -36 V
8 | -36.8 V
9 | 0 V

If something in the above raises any suspicions as to what the problem might be, please let me know!

I've been going over the PCBs, but haven't yet found any obvious short or bad joint, but I'll go over them again (and again, and again...) What fun!

[PinkFloyd]

From the picture of the PSU board the TR2 pads appear a bit brown?... it's possible this has burnt out.....

[ehx]

Success!

Thanks for all the replies and tips guys!

I found and corrected the problem.

It seems that I had managed to cause a crack in the copper print on the top pcb right next to the pad where C10 connects to D6.

(I noticed that it was a bit loose when I picked on it... and also, there where sparks when I did so... ;D)

I scraped some of the varnish from the adjacent track and bridged the gap with a bit of solder, now the heaters light up and the amp is working again.


For future reference, this is how the voltages now measure on the pcb connector terminals (with boards connected and powered):
Pin | Volts DC
1 | 0 V
2 | 30 V
3 | 0 V
4 | 0 V
5 | -30 V
6 | 15.3 V

Thanks again, now I'll be off to listen to some music!

Cheers,

/Erik