New Amp Problem

[HoratioCaine]

It looks pretty inevitable given that I'm no tech expert when it comes to amps that I'll most likely have to take it in for repair, however I may as well ask to get an idea of what the issue might be.

Anyway, my JCM 900 SL-X 2500 head came today.  I was happy and looking forward to using it.  Did the usual, plug it in, get it all set up.  Turned it on, all good so far, red light on, turn off standby switch, still seems ok.  Then, turn master volume a bit to hopefully get a sound.  Nothing.  I was turning it up and down, and all I could hear was a crackle and scratchyness, as if something was blocked.  It also makes a bit of a pop when you turn it off.

From what I could see the power tubes were glowing, but again I didn't want to mess with anything given I am no tech and don't want to fry myself.  I have obviously contacted the eBay seller I got it off as it should have been working.  Maybe something got knocked lose in transit but I don't know for sure.

So, to all you techs here any idea what the problem could be?  Again, I'm probably gonna have to go down to Martin at MJW to get it serviced and fixed most probably anyway, along with the usual retolex to red.

Its a pretty unhappy new amp day at the moment, although I have had a few amps and this is the first one that I have ran into a problem with, I guess it had to happen sometime.

[Twinfan]

I'd take the back off and check all the valves are sitting properly - they can get knocked in transit.

Fire it up and see if they're all glowing.

If all's OK and you still have the problem, it sounds like a trip to a tech is required.

[darkbluemurder]

In addition to Twinfan's comments you could do the following:

- if the amp has a loop (I think it has one) plug the guitar in the return jack. Do you have sound? If yes, the power stage (phase inverter and power tubes) seem to be OK. If no, take the amp to a qualified tech.

- if you had sound in test one, take a short patch cord and bridge the send and return jacks. Often they do not make good contact. See if it works now. If it does not, take the amp to a qualified tech.

Good luck
Stephan

[HoratioCaine]

Thanks for the advice.  Just done the valve checking making sure they are snug and still no sound.

I also did the FX loop thing.  I did get sound when just plugged in through the return jack, albeit a muffled clean sound.  However it still does nothing when I run a cable through both send and return jacks.

Looks like a drive down to the tech, I was going to get it serviced anyway, however I didn't expect or want this problem to occur.  

I'll have to ask Martin if he has any time available yet, and if not then I suppose I may have to find somewhere else since the seller has kindly agreed to offer me a partial refund upon when I get a quote of how much the issue will be to fix.  Sounds obvious saying that but there are a lot of sellers that would refuse to take any responsibility and help for something like this, so I am grateful there.  I don't want to make the seller wait long.

Does anybody have any other reputable tech/shop recommendations near Doncaster please for this problem just in case I have to find an alternative?  Much appreciated.

I reckon the amp will sound fine for me once working, its just frustrating I cannot hear it yet.

[Transcend]

It sounds like it could be a valve problem but possibly not.

if you cant find a good tech i am in wakefield and will happilly take a look at it for you.

And just so you know i arent a fool poking around look up my threads about building a soldano clone etc.

[HoratioCaine]

Thanks for your kind offer, your Soldano clone was very cool.  I asked Martin a bit ago though and he said he can have a look so I'm going over there tomorrow, thanks anyway for letting me know though, it is appreciated.

Hopefully the problem won't be too bad.

[Transcend]

I cant imagine its something terrible to be honest it sounds like its going to be something that will be a cheap fix.

best of luck getting it sorted im rather fond of the JCM900 SLX

[Dmoney]

i just had a similar thing happen with a Laney AOR.
16ohm output didnt work, but the 8ohm did. I measured across each secondary on the OT to common and it looked exactly like the working AOR... when I fired it back up, it worked fine on 16ohms. Something weird in the jack socket or with the switch maybe? I was worried the OT was totally fried as everything else looked fine.

goes to show you... valves amps are little characters!

[jpfamps]

Check that the pre-amp valves are lighting up (you will need to remove the covers).

The pre-amp valve filaments are run off a DC supply (to reduce hum), but the bridge rectifier in the supply is notorious either for failing or having a dry solder joint in these amps (and indeed in other Marshalls such as the DSL401s).
If the pre-amp valve are not lit my guess it that this is the problem.

Indeed I had an SLX in the workshop a few weeks ago with exactly this fault.

It's an easy fix (if this is the problem).

[blue]

as a little aside, apparently the 2500 JCM900 benefits from just putting a patch cable across the effects loop and adjusting the fx return to taste.  supposedly gives a stronger, ballsier sound.  i actually have a 2500 (not the sl-x version)  and always remember about this after i've played it!  so i haven't tried it yet :)  maybe tonight...

anyway, good luck with the amp, hope it is something simple

[HoratioCaine]

Thanks for all the help and support people. :)

And the problem was indeed the bridge rectifier!  There was a dry solder joint which wasn't fully connected on.  This caused the V1-3 preamp valves to not work.  Either way it needed replacing.  Martin has put a brand new one in that is much bigger and can easily take the heat now, so this problem won't happen again.  A capacitor was replaced as well as it had bulged and expanded, presumably again from the heat/stress.

I'm happy now, big thanks to Martin for fixing it for me, I'm looking forward to trying it out later (just got back from long drive!).  If it was good enough for Phil Collen then I am sure I'll like it, something/instinct just told me to get one!

[Dmoney]

nice!
glad it worked out.

[HTH AMPS]

I've fancied one of these amps for a while - I'll pick one up some day when the right deal comes along.

The transformers look a bit 'wee', so I'd likely put something nicer in the amp if it were mine.

[HoratioCaine]

Gave it test and I am happy with it so far.  Like the Jubilee combo converted to a head I had (once it sells in a few days), that I am still looking for in the 2550 head version of, the EQ on my SL-X is responsive which is how I like it.  I am getting a good rock sound out of it which is what I was after.  It is working well with my speaker choice/formation and the cabinet which is good.  I'm looking forward to extending the setup over time.  I am wondering whether to pair it with another cab with 4 G12M's in someday, as I heard it goes well with this amp.

I reckon it is going to sound even better after I get it serviced as it is still not 100% yet to me, one of the preamp valves is going microphonic, so I'll replace that, and a service in general again I reckon will make it better.

I read about the transformers being smaller and not sounding as good as previous Marshalls.  I don't have a problem with the ones on mine personally, it has the Drake Transformers and they sound good enough for me.