2 X QSC RMX2450 for £200?

ceharden wrote: charlysays wrote:   Are they difficult to replace or hard to get hold of then? They work great now. I went mad with the IPA contact cleaner. Only one was a bit crackly and caused that channel to have 100MV dc offset. but all felt quite stiff. There's no resistance at all when turning them now, they feel pretty loose.   If the problem recurs I'll think about refurbing them, cheers for that.   How do you tell if the caps have gone bad? I guess they can dry up but still look fine and can bulge and leak. Can't see any bulging or leaks.  The pots are actually meant to be quite stiff, they have a fairly viscous grease on the shaft which makes the operation smooth but with some resistance (so they're harder to adjust by accident etc).  If they're now really loose then it just means you've washed all the grease out with the contact cleaner.  I try to be very sparing with contact cleaner for that reason.  I've also found that just squirting it in doesn't really do a good job. You can get hold of replacements quite easily but I was finding that the ones I was removing weren't worn out, just needed careful dismantling and cleaning.  I used to have some RMX's myself and looked after some installs that had them so it was useful to get at least one extra round of usage from them.  They probably fail quicker in an install in the corrosive environment you tend to get and because they never get moved. Caps are a tricky one.  Bulging can be a sign, especially if it's at the bottom so you find they're no longer sitting flat and vertical.  Doming of the top of the cap can be a red herring if it's just the plastic insulation and not the metal can. If you can push it back down with your finger that's not a sign of wear-out.  The other sign might be an increase in mains hum on the channel or possibly less power/earlier clipping.  If they seem to be working fine then nothing to worry about.  Electrolytic caps don't like high temperatures so plenty of airflow in and around the rack (applies to all amplifiers) is always good.

charlysays wrote:   Are they difficult to replace or hard to get hold of then? They work great now. I went mad with the IPA contact cleaner. Only one was a bit crackly and caused that channel to have 100MV dc offset. but all felt quite stiff. There's no resistance at all when turning them now, they feel pretty loose.   If the problem recurs I'll think about refurbing them, cheers for that.   How do you tell if the caps have gone bad? I guess they can dry up but still look fine and can bulge and leak. Can't see any bulging or leaks.

ceharden wrote: You can 'refurb' the RMX pots.  I've posted this before but the problem with them isn't the carbon resistive track, it's the silver plated 'common' track in the middle which tarnishes. With a bit of care you can actually dismantle the pots to gain access to the track, then with a bit of contact cleaner on a cotton bud, remove the tarnishing and reassemble. The only other issue with the RMX's is that the electrolytic caps aren't the best and don't have a particularly long life.

Got em... amps are prettty clean and not beat up. He threw in some IEC cables and some nice neutric bridge cables too.
Did a full test today. Everything fine apart from a crackly pot on channel 2 on one amp.
That channel also had 100mv DC offset.
Took the lid off, blew the fluff out and blitzed the pots with contact cleaner. They don't feel stiff anymore.
However I must have got contact cleaner in the small ribon connector behind the pots and not got it out before switching on as when I turned it on both the signal lights were stuck on and I could see arcing coming from the connector when I turned the pots.
Blew the connector out with compressed air and it seems fine now.
DC offset is 22-24mv on both channels now, no crackling and plays music fine.

When I had it on with the wet ribbon connector I had no music going in or anything connected... all seems to be well so no harm done?

Internals look good, not dirty really. A bit of mysterious black hairy fluff wrapped around some of the legs of the transistors etc but all gone now. No bulging caps anywhere. Not looked at the other one as it was working perfectly but will clean it out and clean the pots making sure I don't switch it on with that ribbon connector full of contact cleaner lol


Edited by charlysays - 15 March 2017 at 12:56pm

Berry EP is a copy of RMX with smaller power supply

I've noticed an increase in all RMX on eBay