Fender Studio Eighty Five Problem

[ahenobarbus]

Hi, I'm new here, and I'm trying to know what the problem is with this amp I bought. The previous owner replaced the speaker and did a general manteinance job on the amp. When I brought it home it seemed  fine, but then when set the volume to 10 it isn't as loud as it should. It seems as if even my brother's Pathfinder 15r is louder...

I installed a killswitch on my SG and after that it all sounded very noisey, with lots of feedback on high gain settings. There's also a scratchy noise when I roll the volume pot. I thought I messed up the wiring on the guitar, but trying with other guitars does the same, and rolling the volume knob on my guitar plugged on another amp works fine.

I think I soldered the switch with the guitar plugged in, could that have messed up something on the amp? Thanks in advance, I hope to fix it soon, its such a lovely amp. 

[phatt]

Start with simple stuff; Jumper/bridge the *Effects Loop* with a known good guitar cord. If that improves things then the contact inside the return socket is likely not making a good connection.

Yes not a good idea to work on the guitar electricals while plugged into the amp,,, but still it's unlikely to have caused the drama.
Phil.

[ahenobarbus]

Thanks for the response, I tried it and it didn't work. Then connected the preamp out to another speaker to check if the jacks worked properly and I got the same scratchy noise from rolling the volume knob, but it seemed to have a louder output, and the speaker was smaller...
At last I tried plugging the guitar to input 2 and the noise was gone! The volume problem is still there though, the amp isn't as loud as other smaller amps i've tried. 

[DrGonz78]

I would bet then that there are some cracked solder joints on the input jack # 1. Just re-flow some solder on the joints of the input jack 1 and that might fix your problem.

[ahenobarbus]

SO I was afraid of opening it, but when I did I found this. What are those messy things and are they cheap to replace? Also the jack looks weird.

[DrGonz78]

The jack could possibly be a quick replacement and definitely not stock. Many techs have repaired amps in this manner when it means getting the amp playable for a show that night. Sometime finding the correct jack proves to be impossible at rare times too. My concern would be that the joints that leads circuit boards underside are not in tip top condition.

Also, those are 5 watt cement wire wound dropping resistors, R32/R33. They look like they are at the end of life to me too. I would replace those just by general appearance of the part looking worn out. They generate a lot of heat and the solder joints on the bottom of the circuit board might be degraded, even cracked by this point. Do you have a multimeter? Before doing any replacing of parts it would be good to take some general voltage readings on the amp.

[DrGonz78]

One more thing I forgot to say... I would clean up that top side of the circuit board too. It looks dirty and there are solder bits especially around the input jack area. 99% isopropyl alcohol and some Qtips will help clean up the board area too.

[ahenobarbus]

Thanks for your responses!