Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Found a Fender Deluxe 85 that needed some care: crackle in pots, sound was cutting out from time to time and it needed a good cleaning.

First cleaned the amp, then used contact spray to clean the pots.
I tilted the amp after applying the contact spray, so the contact spray was kept away (somewhat) from the lubricated pot shaft. That seems to have helped in preserving the nice "feeling" of the pot while still cleaning it. FWIW.

The amp was then sounding ok, but after a few minutes of playing the amp still cut out regularly when strumming hard. Web searches indicated that the pcb mounted jacks in these amps can be problematic. So I found some reasonably priced replacements (prices seem to vary quite a bit). The old jacks have a transparent top plate (nuts were quite rusty). The new jacks look cheaper (one big plastic part) but work better.
After replacing all 6 jacks the cutting out is gone.

The clean channel is quite usable, the distortion channel needs quite some tweaking. The parallel channel feature seems rare, haven't played around with it yet.
Nice amp for the price.

Upgrading the Jack inputs seemed to do the trick for a while. But then the amp started cutting out again.
The cutting out happened even with the guitar plugged into the power amp input.
Replacing all the electrolytic caps did not help solving the issue.
Then took the chassis out again and started tapping the components (with non-conductive pen). Found that tapping/moving R82 (0.47 Ohm 5W resistor) caused the cutting out.
After removing the old solder from the R82 joints and resoldering them (with good old unhealthy tin) a half-hour test could not reproduce the issue anymore.
Will test some more later, but this looks a lot better so far.

I don't have the schematic in front of me but I notice a lot Amps from that era have crcked solder joints where ever they use big ceramic resistors.
Big power resistors need a stand off support bracket but to save a few cents they just lay them flat on the PCB which transfers a lot of heat right at the solder pad. The constant thermal cycling eventually cracks the solder. Often it's a hairline crack right around the pigtail on the solderpad.

I opened one amp long ago and the overheating 10 Watt resistor had actually burnt a friggin hole right through the PCB. yikes. :duh  :o
Older tecks would have used metal stand off brackets which resolves any premature failure.
Fender knows it will last at least until the warranty runs out. :lmao:
Phil.

That resistor is used for sensing for current feedback.  It is in series between the (-) terminal of the speaker and ground, which is why there is no sound when it is disconnected.
There was another model in that era that used a 10watt resistor there.  It had even more issues with breaking loose due to being even heavier.  I think it was the 185 or Pro 185.