Dead Fender Stage 185-replacing thermisto

[kepeb]

sorry that wasnt clear 0.01 - 0.02

[Phostenix]

and on the ohm setting
in forward bias theres about 600 ohm and in reverse theres 800.
is that nornal for zener diodes?
kev.

The zeners have the capacitors in parallel with them, so you won't get an accurate reading without removing them (or at least one end of them).

[Phostenix]

theres about 1volt on u9 pin 7 all the others are about 0.01-2v
...

I'm still leaning towards U9. The other opamps are still functioning with the lower voltages or you wouldn't have audio out of the Preamp Out, but it stops there at U9. I'd remove it & see if the voltage comes back up to +-16. How much experience do you have de-soldering components? I'm guessing you don't have a solder sucker, but do you at least have de-soldering braid? It's easy to overheat parts with the braid, so you need to be careful. Give ICs a chance to cool down between legs as you desolder them.

[kepeb]

well i never took an ic out before. i got a sucker but no braid.
i may put a socket in there if i got to replace it.
is this ic expensive/available?

would i be able to use a cr&ppy 741 to test it afterwards?

[kepeb]

the only real problem i can see is that ic is on the fx loop bit of the board which is seperate and for some reason is held in place with some kind of white resin...
how do i remove it from that?

[Phostenix]

If you remove the effects level knob & the nuts that hold that pot & the 2 jacks, etc. from the front, does the PCB have any give? Usually that is silicone sealer type stuff and will peel away or you can cut it with a razor blade. If the solder side is covered in goo, it will certainly make de-soldering more difficult....

[Phostenix]

well i never took an ic out before. i got a sucker but no braid.
i may put a socket in there if i got to replace it.
is this ic expensive/available?

would i be able to use a cr&ppy 741 to test it afterwards?

Solder sucker is great. Braid is nice with ICs to get the last remnants sometimes.

A 741 is a single opamp, so it won't work as a replacement here. TL072, RC4558, RC4559, NE5532, etc. would be acceptable replacements.

[kepeb]

its pretty damn solid... i did wonder about that before
is there any way to bypass the effects loop off board and skip that section or is that particular opamp just on that bit of board by coincidence?

[kepeb]

ok. i'll make a note of the opamps and go ebaying maybe.
although...
i did discover when i finally removed the bit of board, the pre out jack is wrecked.
it fell to bits. i'm wondering if that was shorted somehow inside.

[kepeb]

well it doesnt look like that makes a difference
should i go ahead and remove it then?

[Phostenix]

So, you got the board out? What condition is the Power Amp Input jack in?

Is the trace side of the PCB clear of goop that you can desolder U9? I say remove it & let's see if it makes a difference.

[kepeb]

k. i went ahead any way.
looks like i git 16v on pin 8 without the chip in!

[kepeb]

wow. well that feels like progress.. all the other opamps check out at 16v on pins 4 +8 too

[Phostenix]

Sweet!! I don't feel like all that time we spend yesterday probing signals was a complete waste of time now.

What's the condition of those in & out jacks?

[Phostenix]

If it's possible to keep that sub board safely away from the chassis, I'd love to know if injecting an audio signal onto R135 now will produce output from the speakers.