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Help Diagnosing Vector Research VR-5000

KEB

KEB

Active Member
Picked up a Vector Research VR-5000. I cleaned the pots and board with Contact Cleaner. So far so good. Got rid of the major hickup with Volume and Balance. Much smoother but when adjusting Bass control it swings into high gear and makes my speaker woofers jump out of the speaker, almost. Really weird and wrong. Plays fine if I leave it alone. Wondering if anybody recognizes this behavior? Any thoughts appreciated. I can give more info if the right questions are asked. Thx.
 
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Usually woofers jumping around is from DC on the controls - the tone amps are isolated by caps 260 and267, 360 and 367. However, it is rare that both channels should go. Which raises the question, both channels? and all inputs? Oft the top of my head, can't come up with one thing affecting both channels...
 
sregor said:
Usually woofers jumping around is from DC on the controls - the tone amps are isolated by caps 260 and267, 360 and 367. However, it is rare that both channels should go. Which raises the question, both channels? and all inputs? Oft the top of my head, can't come up with one thing affecting both channels...
Click to expand...
It's just the left channel that has the issue.
 
Junk pot is my guess. Similar to when I hit the volume pots with inappropriate contact cleaner in my Yam cr-820. Ruined in 30 seconds. Live & learn, I did! Your situation may be different as I hope it is.
 
sregor said:
Usually woofers jumping around is from DC on the controls - the tone amps are isolated by caps 260 and267, 360 and 367. However, it is rare that both channels should go. Which raises the question, both channels? and all inputs? Oft the top of my head, can't come up with one thing affecting both channels...
Click to expand...
Can I test this easily? Is it DC offset? I can check that.
 
KEB said:
Can I test this easily? Is it DC offset? I can check that.
Click to expand...
Not DC offset. The tone control circuit is separated from the active components by capacitors 260, 267, 360, 367. Between those two pairs ofcaps there is no connection to power, so there should be no DC on any of the pots. Just check ground to the pots - should be zero DC. As you said left channel, I believe that is between caps 260 and 267.
 
sregor said:
Not DC offset. The tone control circuit is separated from the active components by capacitors 260, 267, 360, 367. Between those two pairs ofcaps there is no connection to power, so there should be no DC on any of the pots. Just check ground to the pots - should be zero DC. As you said left channel, I believe that is between caps 260 and 267.
Click to expand...
Okay. Thank you. Cap replacement is planned. I have a friend who will do it for me. I am a novice when it comes to electronics.
 
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