Help with Mark IV problem

[Phendaphil]

I seem to be having a little trouble with my mark iv. 4 weeks ago mid gig it made a cough and splutter and blew it's fuse. I decided (perhaps wrongly) that this was the power tubes. I thought replacing them had cured the problem, but tonight turning the amp on - there were no lights on - fuse had blown again. I had no option but to replace the fuse - it got me through to the end of the gig.

If any one can give me some advise on any thing else to try - or failing that the name/number of a good technician in the UK (in the north if possible) A few points that may help are :-

Apart from the first time, the fuse seems to have blown either on switch on or switch off. I'm assuming switch off as i never get as far as turning the standby on. The amp just appears dead when i come to use it.

The fuses the local shop gave me look slightly different in design (they are the same rating)- the shopkeeper called them anti-surge rather than slo blo - is that the same? The fuse wire looks a bit like a spring in a cone shape. Pushed to one end of the fuse. The original one was the same size fuse wire all the way.

Many thanks - Phil

 

[Boogiebabies]

I would use only a verified SLO-BLO !!!!

It may sound strange, but I have replace bad tubes with new bad tubes right out of the box.

The second place I would start would be a visualy inspection to see if anything has poofed.

Next, I would think it was from France and give that Nancy a proper thrashing...

 

[Monsta-Tone]

I would use only a verified SLO-BLO !!!!

It may sound strange, but I have replace bad tubes with new bad tubes right out of the box.

The second place I would start would be a visualy inspection to see if anything has poofed.

Next, I would think it was from France and give that Nancy a proper thrashing...

Can I get an Amen my Brothers??

 

[Phendaphil]

Well i managed to find out today - an anti surge is the same as a slo blow fuse over here. I've got the chassis out now - I take it i'm looking for burnt caps/resistors? Is there any place i should be giving extra attention?

Unfortunatly i live in an apartment so no thrashings yet!! Got four gigs this week don't know if i dare take it. Might have to take the Mark III out - shame the FX loop dosn't work as well - and i have an axess midi switcher for the iv. I did talk to an engineer who said the only problem would be if i sent it in and he couldn't replicate the problem - he might not be able to do anything, i might just send it in anyway - it's starting to make me nervous to take it on gigs, in case it goes bang big time!!!!

 

[Monsta-Tone]

Be really careful while looking in the chassis. The Capacitors can hold a charge for days in some amps.

I got careless once and 400 volts DC doesn't feel good at all.





If you have another set of new tubes, try them with a new fuse. I have found a few bad tubes in new sets.

If you can get the problem to re-occur a few times, then your tech should be able to do it also. Maybe you could leave it with him for a few days and he could keep trying it until it fails.

 

[Boogiebabies]

What year is your MK IV?


I would try a 3rd set of power tubes and go from there.

If you have the chassis our, look at the top right hand of the main circuit board for the 2 47uf 100V nichicon caps. Make sure they are intact. There should be two resistors right next to them of the same value. Make sure these are not smoked. Also, look at all the resistors on the power tubes.

 

[Phendaphil]

I think it's a 95, it has the satellite function, and the smoother vinyl. I've just done two gigs with no problems. Will drop the chassis again in the next couple of days and have a look, thanks boogiebabies

 

[Phendaphil]

Found out it's happening on immediate power up - (i checked the fuse just before it happened) - amp on standby. I had a look around couldn't see any burnt parts, or find any strange smells. Could the power tubes still cause the fuse to blow even with the amp on standby? I'm going to try and get some fuses from the boogie distributor as the ones ive been supplied look different, even though the shop insists they are the right ones.

 

[NoGlassNoClass]

My Triple-Rec was popping fuses on standby...turned out to be a bad rectifier tube. I know that doesnt really apply to your mark, but a bad diode maybe?

 

[Phendaphil]

Thanks Noglass - i've now been given the number of a tech fairly local to me, i just hope it misbehaves whilst he has it, sometimes i can play 3 gigs no problem.