Mark II with possibly faulty power transformer

[seedynaturalist]

Hello--I have a Mark II. Recently, I started playing it and it sounded fine. After about 15 minutes of playing there was some kind of surge of power. The power transformer started smoking (or at least I think it was the power transformer that was smoking) and then the fuse blew.

So this afternoon I removed the power transformer and I connected it to the AC. It did not smoke. I checked the red and green wires and found AC voltages ranging from 290VACrms and 35VACrms. I don't know what each tap is supposed to be. This transformer has the code MESA 60-162318 EIA 606-829 imprinted on it.

My question is, could it be that I have a faulty power transformer? Could the reason it didn't smoke after I bench tested it is because I had no load on it? Does anyone have any experience with this problem? I just want to make sure whether it is the transformer that may be the problem or something else before I pony up for a new one.

Thanx

 

[seedynaturalist]

Oh, and the voltages on the red and green wires were in reference to the neutral AC.

 

[Octavarius]

Did you check the power tubes? That's the most likely reason there was smoke, as well as the popped fuse.

Could be a filter cap as well...

 

[seedynaturalist]

No, haven't checked the power tubes. I'll have to reinstall the transformer and unfortunately I didn't keep track of the red wires before snipping them. Well, live and learn.

Anyone know which red wires go where? I know one is for the chassis, that's easy enough, but the other three..........?????

 

[phyrexia]

Your amp started smoking so the first thing you did was remove the Power transformer???

Why don't you put down the soldering iron and take it to someone who knows how to diagnose amps?

 

[seedynaturalist]

I removed the power transformer because THAT was the item that was smoking. The mistake I made was that I didn't label the wires before disconnecting which isn't a problem except for 3 of the red wires. Fact is, the amp was given to me by someone who said if I fixed it I could have it.

If you don't have anything constructive to say don't bother replying. I don't need the useless remarks thank you very much.

gts--I'm not sure which Mark II it is. I will have to check again.

 

[Octavarius]

I removed the power transformer because THAT was the item that was smoking. The mistake I made was that I didn't label the wires before disconnecting which isn't a problem except for 3 of the red wires. Fact is, the amp was given to me by someone who said if I fixed it I could have it.

If you don't have anything constructive to say don't bother replying. I don't need the useless remarks thank you very much.

gts--I'm not sure which Mark II it is. I will have to check again.

I didn't even know transformers could smoke.. :?

Anyway, as I mentioned previously, power tube failure is the most common cause to smoke and blown fuse, and when you say you're not completely certain the smoke was coming from the transformer, it might as well been coming from the EL34/6L6 next to it.

I'd reconnect the tranny and diagnose the amp further. Here's the Mark IIC manual, which contains a lot of useful maintenance and diagnosis information that's worth reading!

http://mesaboogie.com/manuals/Mark%20II-C%20Manual%20-%20Maintenance%20&%20Repair.pdf


I'm also sure that Boogiebabies will chime in very soon and give you the correct wiring instructions. :wink:

 

[Boogiebabies]

The biggest smokers would be the screen grid resistors, filter caps and the Varistor. I would have checked the voltage when the amp fired up, before it blew the fuse and grabbed a Cohiba. Since we do not know what MK II it is, I cannot even begin on the wiring. For diagnostics, you need filter caps, bias caps, new tubes and a digital camera so you can't forget where things go back.

 

[seedynaturalist]

Thanks Boogiebabies---It is a Mark IIA. I appreciate your comments. I will check caps and tubes. I have a schematic and I'm pretty sure I can figure out the transformer wiring. I have a breaker on the AC line to keep any fault condition from damaging more of the amp.

 

[Harry the Horder]

If you look at the MkIIb 1981 Old friend post it's got a nice picture of those three wires.

 

[gonzo]

thanks harry..

i just tripped across this.. thought i'd repost this pic, just in case it might help...


here's my 1981 Mark 2B, 60W w/GEQ

about a year ago, i had it completely gone over, with new caps and replaced anything that was out of spec.