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Is my old amp worth repairing?

 
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777qqq



Joined: 07 Jun 2008
Posts: 2

PostPosted: Sat Jun 07, 2008 10:51 pm    Post subject: Is my old amp worth repairing? Reply with quote

I have a very old amplifier. From the late '70's I guess. Here's the description from the amp: Modular Component Systems, 3845 Stereo Integrated Amplifier, MCS Series, Model #683-3845-8901, distributed by JCPenney, etc. The volume goes up and down slowly while using both my tuner and cd player with it, and the sound becomes more distorted the longer I play the amp. It has one or two other symptoms that I don't remember because I haven't played it in so long. An electronics repairman friend of mine replaced the capacitors I believe, but that made no difference. I'd like to try to diagnose and repair it myself without taking the amp to a shop out of both curiosity and cost savings. I have no understanding of electronics. Where should I start? Is it worth trying to repair it? How durable are amps? Should they last decades? Both the equalizer and tuner that I bought used with the amp still function well. The amp, tuner and equalizer look like they came as a set. I bought the set a couple years ago. Does anyone know approximately how old the amp is and where I could get a catalogue or more info on any component? The tuner is: MCS Series, FCC Data Model no. 3701, etc., and the equalizer is: ADL stereo frequency equalizer, Sound Shaper Two MKIII, Model SS-2, ADC Professional Product Group. How good are these components? Thanks for any replies.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sat Jun 07, 2008 10:55 pm    Post subject: Reply with quote

Have you pulled the knobs off and sprayed them with contact cleaner?
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777qqq



Joined: 07 Jun 2008
Posts: 2

PostPosted: Sat Jun 07, 2008 11:41 pm    Post subject: Reply with quote

No I haven't, but why would doing that do anything about the problem I described? What kind of cleaner would I use, WD-40?
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PostPosted: Sun Jun 08, 2008 4:09 am    Post subject: Reply with quote

You don't need to clean the knobs, but hot soapy water and a small nylon brush will clean them if they are dirty.
What Minnie meant was the potentiometers behind the knobs. 'Contact Cleaner' comes in a spraycan. You will need to turn or slide them as you spray cleaner into them.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sun Jun 08, 2008 4:10 am    Post subject: Reply with quote

The knobs are actually rheostats. Not the plastic knob but the metal encasing. Look for electrical contact cleaner. What happens a lot of time dust builds up on the internal contacts (in side the pot/rheostat) and what the cleaner does is, clean. Volume changing by it's self, crackling, muffled volume. I had an older radio of a friend where no or low volume came out. I took the radio apart and sprayed contact cleaner directly into the pot/rheostat. Worked like a charm. The internal looks like an encased round base with a stem sticking out that the knob sit on. You need to get the cleaner in side the base. Usually pulling the knob off and spraying down the stem gets into the base (round part) and turning the stem back and forth cleans it.
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PostPosted: Fri Jun 13, 2008 6:16 pm    Post subject: Reply with quote

I tried the contact cleaner. It didn't work. I sprayed the rheostat a couple times, turned the knob several times, tested the amp, and it had the same problems. I then sprayed the rheostat several times, turned the knob many times and let the amp sit for a couple days, and it's the same as before I sprayed it. Here are the symptoms. All of these symptoms happen sporadically: the left speaker will have sound but not the right, the right will have sound but not the left, when I increase the volume when one only speaker is playing both will play, the sound fades in and out, the sound cuts off, the speaker sound will shut off when the sound from a radio station pauses (e.g. a person pauses in their speech), both speakers have static, one speaker will shut off but not the other. What should I try next? Should I just replace the rheostat? Are rheostats available for an amp this old, and are they expensive? Thanks for any replies.
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