Fender Deluxe 85 no worky

Longtallronnie

Mate's lent his old SS Deluxe 85 which isn't in the best of shape atm. I haven't plugged a guitar in yet but when you turn it in it buzzes like fuck. There's also a loud pop when you turn it off. This seems to be louder the longer the amp's been on for. 
Min waiting for Fender to hopefully send a schematic but in the meantime, anyone got any ideas? 
First thoughts are there's a dead cap causing the popping noise but not seen anything obvious yet. 

ICBM

Could be a dead cap, a failed solder joint on one of them, or a problem with the Zener diodes and/or their resistors for the low-voltage supply. I've also occasionally come across shorted preamp ICs - usually the first input stage, although not always. They're worth fixing though - not hugely valuable but quite decent sounding, especially the clean channel.

Just make sure you identify all the possible faults first so you don't have to take the board out more than once! And don't test it without the heatsink rail bolted to the chassis, the power transistors overheat very quickly.

The Deluxe 85 schematic and layout are available here: https://www.scribd.com/doc/27558787/Fender-Deluxe-85

Longtallronnie

Thanks for that @ICBM, unfortunately the resolution on that schem is so low I can't read it! I've emailed Fender support so fingers crossed they can send a higher res one.

Looks like an input jack has been replaced at some point and the power led was loose but not gone too deep yet.

ICBM

Longtallronnie said:

Thanks for that @ICBM, unfortunately the resolution on that schem is so low I can't read it! I've emailed Fender support so fingers crossed they can send a higher res one.

Damn, you're right! I zoomed in on it and it just got bigger and still unreadable .

All the amps in this series share most of the circuit elements though, so you may be able to work it out from another of the models if you can find a clearer one.

Longtallronnie

I did print out one for a Studio 85 by mistake but binned it when I noticed it was the wrong one. :-/

Couple of the bigger 5W resistors look like they may have gotten hot but they test out ok and the tracks connecting them are fine. 
Checked the Zeners and bridge rectifier diodes, all good and the large electrolytic caps are ok. 
Power transformers are both ok as well. 
Gonna leave it there for today and start again tomorrow. 

Longtallronnie

Well, I put it back together and turned it on...
The buzz has gone and it works! It still pops when you turn it off and I'm not sure what I did but hey ho. 
I'm guessing I remade a bad solder joint when I was lifting component legs? 
If Fender come up with a decent res schematic I'll delve a bit deeper but until then it'll do. 
Clean channels not bad, very spanky, the drive channel is predictably shit but it's just for noodling on. Will try some pedals through later. 

DJH83004

I have got a PDF of the 85 parts list, board layout and schematic if you need it. Just PM me your email address and I'll send it over. 

Longtallronnie

Cheers, pm on its way.