Wrong voltage on speedball big board [resolved]

[Paul Birkeland]

No sound could be a loose wire/bad connection, or something else.  Have any voltages changed?

[illusineer]

Voltages haven't changed, any connections in particular I should be looking at? Maybe one of the terminals is changing voltage only when I'm not checking lol

[Paul Birkeland]

No sound would have me looking for debris across the RCA jacks shorting them out, loose or broken wires going to or from the volume pot, or loose/broken wires going to and from the headphone jack.  Many of the other problems that would cause a channel to drop would also make very noticeable voltage issues.

[illusineer]

I resoldered some more joints, checked voltages again. Now OB is getting 196V and B+ is getting 230, others didn't change and these two LEDS stopped lighting up (or maybe they were never lighting up?). Also looked at the RCAs and there doesn't seem to be any continuity between their underside soldered tips and the chassis. The pot seems ok and so does the headphone jack, I can take more pictures if it helps.

[Paul Birkeland]

One black wire on the heapdhone jack looks like it isn't captured by solder.

Is that OB on the big board or little board?  I would guess the big board by your photos.  I would suggest reflowing all the joints on the big board, giving a lot of extra heat to the center leg of the TIP50C.  I would suggest leaving your soldering iron on that middle lug for at least ten seconds. 

[illusineer]

I redid all the joints on the big board and reattached it, readings are

OA - 119
OB - 218
G - 0
B+ - 227

and the same two LEDs aren't lighting up :/

[Paul Birkeland]

There's a broken wire from the board to the socket, or a miswire from the board to the rest of the circuit, or there's still a bad solder joint on the board itself.  The B+ being high and OB being high means that half of the board just isn't allowing half of the 6080 to draw current.

[illusineer]

I looked at the board and the wiring back to the circuit and I can't see anything obviously wrong. It seemed so close to working now I'm not sure what to do

[Paul Birkeland]

You have a solder bridge across one of the LEDs on the bottom of the board.

[illusineer]

Wym where? All I see is the oily looking residue from soldering, is that stuff conductive?

[Paul Birkeland]

Solder bridge, iffy joint, and leads to be trimmed.

[illusineer]

How's that? Good to go back into the circuit?

[Paul Birkeland]

On each leg of each TIP50 transistor, I would hold your soldering iron on there and count to ten, then move on to the next leg.  You can do one leg of the A transistor, then a leg of the B transistor, then back to A, etc. switching off to keep the transistor from heating up too much.

It also looks like maybe one end of one of the 47K resistors needs some more heat and solder.

[illusineer]

OK, so I did all of that, put the leads on the board again, go to do resistance checks, then OB gives me around 4.6 megaohms, and OA doesn't read anything.

[Paul Birkeland]

As long as that's not close to 0, then you pass that resistance check.