problems with my M-500t

Ceruleance · August 2003

I have an M-500t that's been acting weirdly. For awhile now the left channel has not been playing until the volume was turned up, whereas the right channel would play fine. As soon as the volume was up the left channel would play at its normal level and with no distortion. Just tonight however the left channel has been cutting out periodically, something that has never happened before. I have verified it is a problem with the left channel of the amp by switching the interconnects. The VU meter goes to zero when the amp cuts out, so I dont think its a speaker problem, either. I will do some more investigative work, but off the top of their head does this sound like a familiar problem to anyone?

polkatese · August 2003

It happened to my Hafler DH-110 many many moons ago. The culprit was dirty connection on the volume potentiometer. I cleaned the potentio using those aircan and brushed the connection solders with small brush, and voila, it's fixed...

Tour2ma · August 2003

Cer,
Also try switching speaker leads as well and see if problem stays in left channel. Could be the amp is protecting the left speaker.

Ceruleance · August 2003

good call polkatese, problem seems to be gone, initially. Man this thing was a dusty ****, probably hasnt been opened and dusted in 20 years. Thanks again, saved me a lot of trouble trying to figure out the problem by myself.

Tour2ma · August 2003

Glad it's fixed... but pre-amp issue doesn't make sense given that problem stayed with the left channel when you switched IC's...

polkatese · August 2003

glad to help, also, watch for loose solder (due to aging and cracking.) Assuming that there are two stacks of connections, gently wiggle the cables and see if the solders move. If so, you might want to resolder the connection, and cleaned the connections using alcohol/spirit. Other than that, you should be on your way...

Ceruleance · August 2003

thought it was fixed, guess not. Oh well, it plays fine when the volume is up, and when is that not the case?:D I may still mess around with it later, check for loose solder like you have mentioned.

tour, left channel with respect to the amplifier, not with respect to the recording. Its def an amplifier issue.

Tour2ma · August 2003

Cer,
Swap the speaker leads...

RuSsMaN · August 2003

(nothing to add at this point, just staying tuned for further developments)

Ceruleance · August 2003

switched speaker leads at the amplifier terminals, so that what was designated as the left channel for the amp was actually driving the right speaker, vice versa. Problem stayed with what the amp classified as the left channel (the left VU meter) and switched to the right speaker with the low output, indicating its an amp problem and not a speaker wire/speaker problem.

One thing I observed was that it seemed like the speaker on the good channel was playing low and then clicked in when the volume was turned up, and then the speaker on the bad channel would click in from not playing at all if you turned the volume a little higher past that.

Once the speakers click in, I can turn the volume all the way down to zero on the preamp, then back up at points below how loud it had to be to click in, and the amp behaves as normal. It seems exactly like the circuit in one of those auto-on subwoofer amplifiers, the volume has to be loud enough for it to kick in, and then it remains on..

So, what gives?

P.S., all this speaker lead switching is easier said then done, I have to crawl into the pit under the table where my equipment rack is with a flashlight and do a lot of painful turning, I wish the M-500t had binding posts.. Thats something I have been meaning to upgrade.

Tour2ma · August 2003

Ok, now you're definitely narrowed it down to a left channel issue.

Sounds to me like a resistance issue in the left channel. Once you overcome it, it stays overcome until the next use.

It may be an issue with the left channel input jack as polka suggested, but I am going to guess a circuit component is giving up on you. At any rate checking and cleaning the left ch inputs is fairly straightforward. For cleaning use toluene, it's common finger nail polish remover.

Here are the numbers for Carver/ Sunfire.
Phone: 425-335-4748
Fax: 425-335-4746

Their CS is not Polk level, but they do get the job done. They will quote you a bench rate for service. Probably in the $150 neighborhood.

If you are a DIY knid of guy, the service manuals are available.

(any thoughts now Russ?)

Ceruleance · August 2003

I have a service manual, but its sort of an intricate diagram, doesnt really address what parts are what or how to fix anything. Any kind of service is out of the question, no way would I put money into a 20 year old amp, and I can almost get another one for $150. I really dont mind the problem, I can just turn it up, but if the left channel is eventually going to die, it would be nice to have a heads up about it.

goingganzo · August 2003

try replaceing the pot or it is a bad transistor or sothing aplying power like a restor that is bad and wont let the amp work unless it is turned up. try replaceing the pot. if you cna soder it is prety easy if you can get to the back of the bord.

rskarvan · August 2003

What you have is a single bad transistor in the left channel.
Hmmm.
It could be one of the main power transistors.
Or, it could be a teeny tiney transistor in the circuit prior to the power transistors.

Anyway, its a $2 part and no big deal to fix.

A repair should cost you about $50 or so at a good electronics shop. FYI.

Ceruleance · August 2003

thanks for the help, if it dies i will take it in to get it fixed, otherwise i will deal with it

I have another M-500t in mint condition I can use anyways.

Airplay355 · August 2003

hey guys, same problem with my luxman, channels work fine when its turned up but when its turned down it crackles in and out, and both channels will just stop playing sometimes. i dunno what to do, just letting u know u arent alone lol

Tour2ma · August 2003

AP,
Are you talking about an Integrated Amp?

Airplay355 · August 2003

no its a 2 channel receiver, model number is listed in my sig.

Tour2ma · August 2003

AP,

If your Luxman is an old, analog Receiver, as i suspect it is, in your case it could be the Volume potentiometer is a little dirty and/or corroded.

I have had success in the past with a product called "Electrosolv", which is basically an acetone aerosol spray, in cleaning up old pot's on my original Heathkit and my Yammie C-2 Pre. A shot or two of spray in combo with rotating the pot usually does the trick.

Airplay355 · August 2003

if i open it up how do i find out if the pot is dirty? or where the pot is even?

Tour2ma · August 2003

The pot will be just on hte other side of the face plate from the vol control knob.

My old Heathkit was easy, its pots had holes, but the Yammies was sealed. Still the spray was ables to penetrate along the shaft of the pot and clean it up.

Do be careful to keep the spray off of visible plastic parts or they will be discolored. Usually the cans come with an extention tube, like WD-40 does, to direct the spray.

problems with my M-500t

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