bias issue

[Enzo]

I just did that a half hour ago on an Ensoniq keyboard. The battery is soldered in, and someone had replaced it and tore the trace up under the battery. I installed a coin cell holder, so now anyone can buy a new battery at Radio Shack and snap it in without soldering. But to get the circuit restored I had to run a small wire from the pin of the holder over to a resistor across the board.

[daz]

Are you sure it was wire and not a (ribbed) tube? They will often rip out of the board if you don't have the component perfectly desoldered.

Yes ! No doubt that was it, makes much more sense. It never occured to me but that must be it. They came out on ALL of them tho, and i didn't do anything crazy and desoldered them as well as i could. But i could not get it all no matter what i did so i had to melt one side and tilt the cap then do the other. Maybe it could be done but i had no idea and they were really in there big time. Never seen that before and I've dealt will plenty of double sided boards. Anyways no big deal. Just a few pieces of wire to make my own "traces" as enzo just mentioned and all is fine.

[52 Bill]

Yes ! No doubt that was it, makes much more sense. It never occured to me but that must be it. They came out on ALL of them tho, and i didn't do anything crazy and desoldered them as well as i could. But i could not get it all no matter what i did so i had to melt one side and tilt the cap then do the other. Maybe it could be done but i had no idea and they were really in there big time. Never seen that before and I've dealt will plenty of double sided boards. Anyways no big deal. Just a few pieces of wire to make my own "traces" as enzo just mentioned and all is fine.

This is one of those cases where a solder with a lower melting point would help in removal of the caps. Get yourself a small kit of Chip Qwik and keep it on hand for occasions like this one.

[nosaj]

Anybody notice caps in one schematic are rated for 350v and the other at 400v?

nosaj

[daz]

Anybody notice caps in one schematic are rated for 350v and the other at 400v?

nosaj

The 400v caps are signal caps in the PA vs the psu caps that are 350v. If your point is that the psu caps should be more, i agree. Maybe the issue wouldn't have happened in the 1st place. But thats what was in there and i used 350's to replace them because they are a tight fit and nothing with more voltage was small enough. they are all butted up against each other in a row, so no room for bigger.

[nosaj]

Just the fact that there is no wiggle room as far as voltages go.


Quote: Sounds like there may be a connection failing between the filter caps and the B+ line. It seems to be getting progressively worse, maybe from board flexing? It went from 350V to 325V and now you have the harmonizer note.
As you say, it could be a feed through for the double sided board, but it could also be a cracked pad or trace.
Resistance checks from main filter caps may help, to the ground connection, between the 2 caps and to the B+ line.

[g1]

Those caps in the power supply are stacked in a "totem pole" (series) configuration. So you have the equivalent of a 700V cap. for each of the 3 sets. None of them should be getting near 350V, so you don't need to worry about that. C6 & C7 = 50uf 700V, likewise for C8 & C9, and C11 & C12

[daz]

Those caps in the power supply are stacked in a "totem pole" (series) configuration. So you have the equivalent of a 700V cap. for each of the 3 sets. None of them should be getting near 350V, so you don't need to worry about that. C6 & C7 = 50uf 700V, likewise for C8 & C9, and C11 & C12

I know, i thought about that after i posted and later looked at the schematic. I wonder what DID cause them to leak tho? 5 of 6 leaked and the amp is maybe a year or so old i believe. Maybe leaving it on for long periods....heat?

[g1]

For sure it was leakage and not adhesive? Very strange for a 1 yr. old, but maybe a bad run of caps.

[daz]

For sure it was leakage and not adhesive? Very strange for a 1 yr. old, but maybe a bad run of caps.

Definitely.....big black glob coming out of one leg hole of the worse one, the rest not quite as bad. Besides, it fixed it so that was obviously it. Plus there was adhesive too...white.