Problem with Amp (Mode Four)

[buddyfuzz]

Heya Guys,
I have a mode four here, (yes, I know not everyone is too fond of this amp [img]/images/graemlins/laugh.gif[/img]), and there seems to be a bit of a problem with it. I can turn it on, and the powerlight comes on, however none of the lights which show which channel it is on come on, and the amp makes no sound, also no lights appear on the footswitch. Anyone have any idea what the problem is? I'm not very good with amp/tech stuff, so I have no idea.

Any additional information you need, just ask, but if I can get to the bottom of this, it'd be helpful,
Thanks,
Jonny

[jgcable]

Re: Problem with Amp (Mode Four)

Check for an internal fuse. If an internal fuse blows your power light will still work. Internal fuses are usually board mounted. If your external fuse was blown nothing would light up.

[buddyfuzz]

Re: Problem with Amp (Mode Four)

Ah, does the internal fuse look like a regular fuse from a plug then?

[jgcable]

Re: Problem with Amp (Mode Four)

Yes. It should be ceramic but it might be glass. They will be clipped into fuse clips that are mounted directly on one of the circuit boards.

[zeegler]

Re: Problem with Amp (Mode Four)

Don't touch both sides of the fuse with the amp plugged in. Trust me on this one, it kinda hurts....a bit. [img]/images/graemlins/laugh.gif[/img]

[buddyfuzz]

Re: Problem with Amp (Mode Four)

Ah, I'm gonna try this later tonight, and er.. You've scared me now Zeegler.. ..it's not fatal is it?

[Lordofgain]

Re: Problem with Amp (Mode Four)

Generally not fatal but you might be twitching a bit for the evening [img]/images/graemlins/smile.gif[/img]

[mrr3000gt]

Re: Problem with Amp (Mode Four)

Touching both sides of the fuse block could very well be fatal, as its likely that the B+ (main internal power) fuse may be blown. If so:

1) Something caused it to blow: most of the time its a bad power tube.
2) The amp may use in excess of 450 volts and draw more than 400ma (nearly 1/2 amp) of current: plenty to kill instantly.
3) The filter caps likely are nice and charged with enough voltage to knock you off your feet (or kill), as the fuse helps complete the ciruitry most amps have to allow the filter caps to bleed off lethal voltage when the power is off.

if you are not sure what you are doing, pay to have someone fix it. The cost is much cheaper than a funeral...

[Twisteramps]

Re: Problem with Amp (Mode Four)

Remember too the mode 4 is a solid state amp: I doubt it has the voltages listed in 3000gt's post. However, he's correct if it was a tube amp. And being too cautious is always preferable to not being cautious enough.

Unplug the amp, use a voltmeter to check for continuity on the fuse. If the fuse is blown, replace it with the EXACT same type and rating. This is important - too low a value and your amp could blow fuses even if there isn't anything wrong. Too high a value and it won't blow - and the expensive components the fuse protects will be damaged.

One tip - when at all possible, use ONE hand to work inside an unplugged amp, and use a clip for the multimeter so you don't have both hands inside there. Why? Because if you get voltage going into one hand and ground on the other, it makes a path through your heart - and it doesn't take much to stop your heart. This would make you assume room temperature in a short time and be a bad thing. If you're fishing around in an amp, use one hand and put the other one in your pocket or take up a fencing pose. ;0

If you have a bad fuse, replace it with the same rating/type, and it blows again - take the amp to a tech. You may be lucky and just have had a power spike of some sort that blew the fuse, but if there is a fault in your amp that keeps blowing them, it's time to take your amp to a tech. Doesn't Marshall have a 5 year warranty on their products?

Pete

[Deneb]

Re: Problem with Amp (Mode Four)

5 year transferable warranty I believe.

What Twister is saying comes from an ELECTRICIANS stand point. My teacher used to always say, if at all possible, use only one hand. There are some things you can use 2 for no problem in the danger end, but again, better safe than dead.

You only need a 1/10 of an amp to kill you, and if it catches your body correctly, sometimes less can do it.

I remember discharging big caps with screwdrivers, and shit just came off of the screw drivers, that always got us yelled at!

[Deneb]

Re: Problem with Amp (Mode Four)

The only exception to the fuse rule is this.

If you have a 5A SLO-Blow in there, you can replace it with a 6A FAST-Blow. I wouldn't do it unless I was pressed, and there was no other way (you're at a show, no back up amp, the ONLY fuse is that). If you can't buy the fuse you want at the store, go somewhere else. (What I mean is you can use a fast blow, one value higher than the slow blow. It's not great to, but you can.)

You can usually look at the fuse glass and see if the filament is broken..if it is, guess what, so is the fuse.

[jgcable]

Re: Problem with Amp (Mode Four)

[ QUOTE ]
5 year transferable warranty I believe.

What Twister is saying comes from an ELECTRICIANS stand point. My teacher used to always say, if at all possible, use only one hand. There are some things you can use 2 for no problem in the danger end, but again, better safe than dead.

You only need a 1/10 of an amp to kill you, and if it catches your body correctly, sometimes less can do it.

I remember discharging big caps with screwdrivers, and shit just came off of the screw drivers, that always got us yelled at!

[/ QUOTE ]

We used to do the same thing!! Crazy.

[buddyfuzz]

Re: Problem with Amp (Mode Four)

Er, maybe it's best I take it to a tech, I really haven't worked with electronics much, and I don't feel like dying just yet, lol.

Thanks for all the advice guys,
Jonny

[buddyfuzz]

Re: Problem with Amp (Mode Four)

Hell, I did it.

Er, I've got the fuse now, but I know NOTHING about electronics, and I'm not sure how to tell if it's blown, can you tell by looking at it?

The fuse says it's a 'T4E250V' - does that sound right?

Thanks,
Jonny