Fender Deluxe 85 Volume Issue?

[Uziel]

Hey there,

I recently was given a Fender Deluxe 85 that was in pretty sorry shape as an even trade for an OD pedal I built. After replaceing the first 3 pots (Volume, Treble and Bass) on the face (they were sheared off) I pulled the board out and noticed that there was some pretty good burning (One had actually blown the top of the sand off) around the 115 and 116 wirewound resistors so I went ahead and pulled them and replaced them and also replaced the 2 diodes just below them as they seemed like they had probably felt the heat too. Long story short I went ahead and fired her up and lo and behold I was able to play it and it worked great ....for about 2 weeks. now it seems to have developed this really interesting issue where when I turn it on and with the volume set at about 1.5 it plays quietly, but if I start hammering the strings hard it immediately gains about 10 times the volume and will pretty much sit there. I can turn the volume up or down and it seems to eb about the same level only it breaks up more at around 5 than at around 1. Any ideas as to what could be causing this? I really dont want to take it in to the shop as it is a cheaper amp to begin with and I have already sunk about $45 into it (Fender sure thinks their pots are made of freakin gold O_o) oh , and I also dont want to be beaten by this damn amp . I'm starting to wonder if the replacement pot I was sent was maybe the wrong part since the original was one of those "C" tapers but eh Im not sure now.

Thanks for any help guys!

[52 Bill]

...if I start hammering the strings hard it immediately gains about 10 times the volume and will pretty much sit there. I can turn the volume up or down and it seems to eb about the same level only it breaks up more at around 5 than at around 1.

Welcome!
I'd first start by checking to see if this is a mechanical issue. A cold ground connection may cause this. Does physically jarring the amp cause any noises or volume changes? Turn down the reverb and give it good Enzo thump with your fist. Can you make it do this?

[Uziel]

Hey Bill!

Thanks for the fast reply. Yeah I came home today and went out to the garage and did as you suggested. I couldnt get it to start up quiet at first but I kept messign with it (turning it on and off and adjusting the volume) until it started quietly (volume down) I then grabbed a graphite drumstick and gave it a good whack on the chassis It immediately went into the almost full blown volume (Im assuming, but it sure is louder!). While I wasnt able to get it back down to the quiet volume to test again it did do what you had said that one time. I alo noticed (Since I have teh board completely out and sitting on an isolation box) that there was quite a bit of heat radiating off of the 2 - 240 Ohm resistors I just replaced on the board as well as the 2 diodes which were replaced just below those resistors. One thing I did notice is that when I resoldered the new diodes and resistors in place the trace for the diodes lifted a bit off the phenolic. Could this be the source of the problem? Also, The resistors I had to use for replacement were round encapsualted wirewound which replaced a set of the old square sand resistors. Same wattage and Ohm rating though. Would this make a difference?

Thanks again Bill for the help! Sorry my post is so long >_<

[52 Bill]

...It immediately went into the almost full blown volume (Im assuming, but it sure is louder!).

Well if the problem is mechanical in nature, the first thing to check are the break jacks. Next would be to check for any loose or broken parts on the circuit board.

...there was quite a bit of heat radiating off of the 2 - 240 Ohm resistors I just replaced on the board as well as the 2 diodes which were replaced just below those resistors.

Those resistors and diodes form the low voltage power supply for the ICs. The heat they create is normal, which is why those resistors are 5 watters. If one of these supply voltages were to cut out due to the lifted pad, I would think that the entire amp would stop working, and not just change volume levels.

The shape of resistor is unimportant as long as the correct resistance and wattage is used.

When a copper pad lifts from the board, I try to leave an extended length of lead on the new part, which I solder along the path of the copper trace that leads to the lifted pad.

Sorry my post is so long

When it comes to fixing an amp, sometimes too much information is a good thing!

[Uziel]

Well if the problem is mechanical in nature, the first thing to check are the break jacks. Next would be to check for any loose or broken parts on the circuit board.

Hey Bill!

Yeah I went completely over the board alst night and resoldered any connections that too me looked bad (IE Grey instead of nice and bright silver) I have yet to test today as I am at work until 5 but will get it plugged in and running as soon as I get home! You say break jacks so Im assuming the input jacks? I know on the deluxe 85 models that was one of the biggest complaints was the cheap plastic jacks and how easily they broke. I will check these as well when I fire it all up this evening.

Thanks again Bill!

[52 Bill]

You say break jacks so Im assuming the input jacks?

No, by break jacks, I refer to FX loop or pre-amp out/power amp in jacks.

I would guess that about 25% of all the amps I see for repair are problems caused by dirty break jacks.

These jacks have a normally closed switch circuit that completes the signal path through the jacks when they are not being used. If the switch contact becomes oxidized or dirty from airborn contaminants the signal path opens up and the amp loses signal. The signal loss can be complete or as in your case partial. Usually cleaning the return jack with a spray cleaner like De-Oxit will fix these problems. Sometimes when the oxidation or contamination is really bad, the jack will need replacement.

[Uziel]

If the switch contact becomes oxidized or dirty from airborn contaminants the signal path opens up and the amp loses signal. The signal loss can be complete or as in your case partial. Usually cleaning the return jack with a spray cleaner like De-Oxit will fix these problems. Sometimes when the oxidation or contamination is really bad, the jack will need replacement.

You know I bet your right on the money here. Not only did this amp look like it was tossed from the back of a truck ( 3 sheared knobs and in the verb tank every single spring had broken off and was lying at the bottom) But as I was cleaning it over last night I noticed it seemed to have a film on it aroudn the edges and at places on the board where it almsot looked like it had been rained on / dunked and was left with deposits everywhere.... Man now I cant wait to get home and check it out! Work cannot end soon enough today!
Cheers !