Multimeter/amp tutorial

Lands Leaving

Does anyone know of a good tutorial video or site for using a multimeter on guitar and amp? I've got a ground problem in a champ 600... and have ahd for a few months, and I finally bought a multimeter, but I'm not sure where to start and how exactly to check if its grounded.

Keep all explanations patronisingly simple, I'm not great with this sort of stuff... but I want to learn!

rcaz

Well, if you don't discharge your capacitors properly, you could die... So I'd look for tutorials about that first :pac:

Lands Leaving

Die eh... that sounds almost as bad as the €100 I was quoted to have it repaired in xmusic.

After checking how to discharge capacitors it seems easy enough... but maybe I should bite the bullet and let an expert look at it.

Damn expensive tiny amp!

Is anywhere more reasonable for repairs than xmusic? I don't really want to pay near enough the cost of a new amp to fix it.

DamienH

Discharging the caps is pretty simple, just make sure you do it correctly cause you can get a nasty shock! You should have 2 leads with the multimeter, one red one black, with probes attached.

To make things easier I'd recommend buying a lead with a crocodile clip on the end instead of a probe. Clip this black wire on the chassis, that's your ground. This is connected to the COM terminal of your multimeter. The red wire gets connected to the V terminal, and then you're good to start reading voltages. Turn the dial to a higher voltage than you expect e.g. If you're taking a reading of a cap voltage , say 325V, set the dial to 500V. Double check everything's okay and then turn on the amp.

IMPORTANT: Put your free hand into your pocket so , if you should get a shock, it's not going across your heart. Probe away , but be careful electricity can **** you up! That's about as detailed an explanation of taking a voltage as I can give.

Any quality multimeter has a continuity tester (think that's what it's called anyway). It tells you if there's a connectiong between to chosen points. In your case, between the tip of the red probe and ground (black lead clipped onto chassis). You'll hear a beep if there's a connection. The symbol for this on my MM dial is a diode with a kind of sound wave. All grounds on your amp should ultimately be grounded to the chassis.

I'd say open it up anyway and have a nose before you hand it in but for god sake discharge the capacitors properly! Standby switch , big resistors are all good ways... using a screwdriver with an insulated handle is not!

Eoin Madsen

Lands Leaving wrote: »

Does anyone know of a good tutorial video or site for using a multimeter on guitar and amp? I've got a ground problem in a champ 600... and have ahd for a few months, and I finally bought a multimeter, but I'm not sure where to start and how exactly to check if its grounded.

First, what makes you think you have a ground problem? And second, what kind of problem?

Generally, a broken ground will cause the amp to stop functioning. If you know what's supposed to be grounded, it's just a matter of checking the various grounds with the continuity or resistance meter on the multimeter (resistance should be 0 for a good ground, and will appear infinite if the ground is broken). The amp does not need to be turned on to check this, but you should still be wary of charge stored in capacitors - especially if you suspect a broken ground. Check each filter cap with the voltmeter on the multimeter before you touch anything.

If you have a humming/buzzing problem attributed to ground then it's probably a ground loop and a multimeter won't get you very far.

Lands Leaving

A ground loop sounds right, I didn't know the difference. It's basically a loud buzz which stops when I touch the guitar strings or any metal on the amp chassis, and when I hit a string iot sort of fizzes... same when I touch, say the input jack or on/off switch.

Someone who knows about amps and such looked at it and said it was the ground (but he was too busy to fix it, bah!) but I guess he meant ground loop.

Also I know it's not the guitar, cables or the speaker itself. I've tried different guitars which work in other amps, smae with cables, and hooked the amp section to a different speaker, same issue.

If a multimeter won't help, any idea if I can do anything or is it time to accept that I have to pay for a repair job? (p.s. I'm broke and I'll try anything!)

Paolo_M

Were you not on about this amp before?

A multi meter wont help at all.
Someone who knows what they're doing using a multi meter, along with other tools for fault finding, will help a lot though.

Seriously, learning amp tech skills takes a lot of time, experience and mistakes!!
If you intend on doing repairs full time then by all means learn but if you just want your amp fix then I'd say just bite the bullet and take it to a tech.

Lands Leaving

Yeah I was on about it before, had to put it on the back burner for a while because I was busy with other stuff.

I would like to learn about amp repair, and I've learned a fair bit just from taking it apart and such, but if it's as complex as you say it's probably beyond me at the moment. I just prefer to try sort these things out myself, especially since it's probably something simple that I just don't have the skills to find.