Beloved MCS 3865 Amp Right channel started popping. Thoughts?

[MarkHaslett]

I have been using a Modular Component Systems 3865 in my workshop. It has plenty of power to drive my Technics SB-G800 (97 db/watt) speakers. Have used it for 2 years until the right channel just started popping loudly every minute or less. Needle jumps (yes, one needle still works on the watt meters). Pops are accompanied by a brief static sound. I have some skills with electronics, primarily soldering larger parts, but no technician training. Should I scrap it and use my Kenwood KM 991? Will need a preamp. Is it safe to use the MCS as a preamp despite the pops? Is there a fuse for the amp section?

 

[Dan13105]

Does it pop even with the volume turned all the way down?

 

[painttoad]

my guess would be the 2sa798 in each amp channel. my 3835 had noise but it wasn't popping, it sounded like leaves rustling. regardless, they need replaced.

there are also 2sa726 in the phono stage.

 

[MarkHaslett]

I really appreciate the feedback, although it just occurred to me that an audiophile might think that word has negative connotations. Thanks for the tips and sorry for the delay getting back to you. I could not remember if the popping decreased with the volume, which was a great question to narrow the problem to amp/preamp fault I assume. Two days ago I got the 3865 off the shelf where it sat for two weeks decommissioned. I grabbed a couple of Bose 151 outdoor speakers (4 ohms each) and ran the amp several hours. No popping! Yesterday I put it back on my Technics SB-G800’s and drove it pretty hard. No popping with input via tape monitor, auxiliary, or tuner, with or without active tone controls, in stereo, reverse or mono. I do think the phono 1 & 2 are bad because they pop very loud and sizzle. Is it possible there was a bad jumper connection in the back that corrected with movement? I should add that it plays in my garage heat and humidity in Florida near the (salt)water.

 

[John3655]

Yep the popping can be a sign of a speaker connection making and breaking. Time for contact cleaner, as well as outside connections most likely, it can also be inside the case sometimes loudspeaker connection to PCB.

 

[painttoad]

I do think the phono 1 & 2 are bad because they pop very loud and sizzle.

there are also 2sa726 in the phono stage.

Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing. While following along with others' threads and trying to help out with "consider replacing these...

audiokarma.org

 

[MarkHaslett]

Having little technical knowledge, though I love to repair things, I have been assuming that these numbers refer to capacitors because often people seem to need to replace “caps” in these forums. I have had many pieces of classic equipment over the years, most of which reside now in Colorado Springs with Jerry at Oak Tree Vintage. I have had Pioneer SX 1980, SX 1280, SX 1250, 1050, 1010, and my SX 939 bought new when I was 18. I have owned almost every silver face Pioneer cassette deck, a Pioneer reel-to-reel, Teac A360-S cassette, Kenwood KA-1000 amp (massive amount of damping factor with Sigma Drive), and several beautiful other components and amps. Besides Pioneer, some of my favorites that were Technics and Kenwood. I know power transistors go bad and I assume the symptoms are different than bad caps?

 

[painttoad]

the numbers that i referred to are transistors. that's why i supplied a link to a transistor thread so you can look at the chart for replacements

 

[drumbum]

I have been using a Modular Component Systems 3865 in my workshop. It has plenty of power to drive my Technics SB-G800 (97 db/watt) speakers. Have used it for 2 years until the right channel just started popping loudly every minute or less. Needle jumps (yes, one needle still works on the watt meters). Pops are accompanied by a brief static sound. I have some skills with electronics, primarily soldering larger parts, but no technician training. Should I scrap it and use my Kenwood KM 991? Will need a preamp. Is it safe to use the MCS as a preamp despite the pops? Is there a fuse for the amp section?

slight derail, but do you have any other speakers currently?
Care to share your thoughts on the G800's?

 

[MarkHaslett]

At the time I bought them around 1977, they were top rated in Consumer Reports. They still work like new. Fortunately these were not constructed with foam in the periphery, so they have held up. Great, balanced tone quality and very efficient (97 db/1 watt). So glad I lugged them around all these years! They are not small but also not ungodly heavy.

 

[drumbum]

At the time I bought them around 1977, they were top rated in Consumer Reports. They still work like new. Fortunately these were not constructed with foam in the periphery, so they have held up. Great, balanced tone quality and very efficient (97 db/1 watt). So glad I lugged them around all these years! They are not small but also not ungodly heavy.

I have a pair that I picked up for next to nothing,...because.....well....had to hear 'em.....lol.

Have them in my shop downstairs. Powered them with a QSC series three 3800 for a bit.......didn't seem at all stressed.

I have MCS 8245's sitting on them. (another speaker that has not needed refoaming)