My fender stage 185 amp won't power up

[spindarec]

Yes wiggle the cord and i used the same input jack for the entire test yesterday. I played this morning and test with the two different inputs channels and I got the same problem. When the output signal is lower, the led of my foot-switch are not shining like usual, it shines less. Don't know if it helps.
I've removed the chassis from the cab and i did some measures, to the collector of Q15 I got 53V instead of the 50V.
For R175 and R176 I've got +/-16V et +/-50V on each sides.

[g1]

For R175 and R176 I've got +/-16V et +/-50V on each sides.

You will need to see if these readings are the same during faulty operation and proper operation. Those 2 resistors often need resoldering and could create problems.

[52 Bill]

And if you have not done this yet, check all of the jacks for broken solder connections. And you should clean all of the jacks, pots and switches with a good contact cleaner.

[spindarec]

And if you have not done this yet, check all of the jacks for broken solder connections. And you should clean all of the jacks, pots and switches with a good contact cleaner.

Done and there's no broken solder connections.

[The Dude]

Did you ever remove or replace Q21?

[spindarec]

No, it's still on board. Do you mean it could change something if I remove it ?

[The Dude]

It's a muting FET. If it's leaky or shorted, it could definitely knock down your signal level.

[Jazz P Bass]

The FtSw LEDs dimming is a sure sign that the power supply is not holding up it's end of the deal.
Most likely, those honkin 7watt resistors need to be resoldered.
And those zener diodes are known to get toasty & unsolder themselves.

Fender 185 Series Power Supply.pdf


Q21? Q21?

Oh this Q21?



The one with it's top blown off.

If you do not have a replacement at hand, for testing, you can simply remove it.
A new one should be reinstalled to finalize the repair.

[spindarec]

So yesterday night I've resoldered the two 7 watts resistors and removed J111 for the moment.
I played one hour long this morning and nothing to notice, no signal loss, no buzzes or crackles.
Does it mean the amp's repaired ?
Thanks

[km6xz]

Another frequent cause of signal drop is the effects loop jack switching contacts becoming oxidized. Get a can of CRC Kontakt 60 or Cramolin Contaclean. both of which are sold in France....except on Mondays. Personally I think that is a very civilized tradition. Personal time and relaxation is taken much more seriously in Europe than the US where almost everyone needs to work constantly to keep from going bankrupt.
Spray a little of one of those de-oxidizing chemicals into the Send and Return/Power amp input jacks and work a plug in and out a few time, and repeat every year.
Pull the Q21 transistor and you will probably find that the signal stays up to normal level.

[spindarec]

Thanks Km6xz, when I talk about J111 in fact it's Q21 transistor that I removed yesterday and this morning the signal stay up to normal Level. I'ts maybe too early to say " victory " but it was nice to play like that.
I'll buy a can of kontact and i tell you guys if troubleshots happens again.
Thanks a lot for your knowledge and your sense of " How to repair ". I learned a lot and itīs really cool to repair stuffs
by ourselves.

[g1]

As far as Q21 goes, it's only job is to prevent pops and thumps when you turn on the amplifier. So it will run fine without it, but if you don't like the turn on pops, you should put in a new one.