I bought a used VS65R that had a bad Volume pot. I replaced the pot and it worked fine. I was using it at practice a couple of weeks later and all of the sudden it went to a high pitch squeal. I shut it down but now everytime I turn it on it goes right back to it. I suspected a blown E-cap but visually nothing shows. Any ideas where to start?
This is only a guess on my part, but if the potentiometer you replaced is part of the feedback loop and either of the outside legs are open, the circuit will be infinite gain and have a parasitic oscillation you describe; many gain circuits in pro gear are configured this way. Also, since you did replace the pot, it would be easy for you to check this first to make sure these connections are secure as it may not be a co-incidence, but still related to the original fix. Hope that helps.
SOURCE: Hot Rod Deville, reverb squeal...
Here is an article that might help:http://www.guitarplayer.com/article/reverb-troubleshooting/jun-09/97165 Here is the schematic:http://www.fender.com/support/amp_schematics/pdfs/Hot_Rod_DeVille_Schematic.pdf Check to see if someone hasn't reversed the input and output cables at the reverb tank. Then troubleshoot the reverb section .
SOURCE: original circa 1982 Kurzweil Ensemble Grand
Given its age, this unit needs a little TLC. Units of that vintage used some capacitors that may have dried out a bit and need to be replaced. There are also op-amp ICs internally that may be defective. I would suggest a visit to a service shop that works on keyboards as not all do.
Keep us posted.
Dan
SOURCE: low volume, high pith squill
The schematic is here:http://www.vintagesynth.com/roland/xp60.php Take note though that the design was changed for the newer DD3. Here is a link to a forum with links to later DD3 service notes:http://music-electronics-forum.com/t15879/. Start checking transistors at the input. Check voltage readings on pins on the I.C.s to see if they match the supply voltage at IC10 . If you get voltage readings on pins that aren't supposed to have readings there is a good chance that the I.C. you are testing is shorted. Also check the diodes as you proceed.
SOURCE: Everytime I turn my amplifier on, it makes this
DO NOT FACE THE GUITAR TOWARDS YOUR AMP. IT WILL MAKE IT SQUEAL.
SOURCE: my amp is making a high pitch noise almost like
Bad tube? maybe
Try removing each tube 1 at a time starting at the first preamp (12ax7) If the noise stops after a particular tube is pulled replace that tube with a known good tube. Shut down the amp between tube pulls, Power tubes don't usually cause this problem but I'd pull them anyway,just remember they get very hot.
Make sure all tube shields are on and replaced after tube pull test
The most common cause of oscillation is a open or leaky filter cap,this would require a cap job and unless you have a good knowledge of tube electronics and the voltage dangers present,I wouldn't suggest doing it yourself.
Also if the output transformer was replaced or rewired or the negative feedback circuit was touched oscillation could occur also.
Make sure your guitar cables are in good shape, a cable with a bad shield can cause problems too.
Excessive noise can occur when one of the 1/4" input jacks shorting bars doesn't make contact to ground. A duumy plug would confirm this but you could also plug two guitars with good cables, into each input and see if the oscillation disappears.
Hope this helps
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