SWR Blonde On Blonde help please!

[Appaloosa]

HI, I have a SWR Blonde on blonde powered monitor for acoustic guitar that is not working. When i got the amp most of all the small electrolytic caps were blown as well as the output transistor. I replaced them, and tested all the resistors diodes. when I powered it up the power transformer started to get really hot.

My question is what is the best way to test the p. transformer. i assume mine is bad. cause it got hot. I have continuity between the primary leads, and continuity between the secondary leads. should I see some continuity between the primary and secondary leads if the p.trx is bad? I do not see any continuity between primary and secondary when amp is off and unplugged.

The p. tranx is a mercury Magnetics 560015-120, and I think they want about $150 for a replacement. Is their a cheaper alternative available?

Would some other problem cause my P.tranx to get hot? like a electrolytic cap installed backwards?

Thank you so much for any help?
ps. if any one has a schematic that might help a lot. I believe this is a pre fender SWR amp, Serial # 0157. thank you!

[Amp Kat]

I think if you got a reputable tech to call Fender they could get you a replacement tranny for it and it seems if it had a Mercury in it that someone may have done some modding to it also that it obviously didn't like and my gut tells me it was done in the power supply. Had to be either caps backwards are a higher voltage than the cap was rated for. Can't see why someone would put a Mercury in a SS amp that really wouldn't benefit from it. Actually sounds like they put a tube tranny in it which would explain the blown up caps and why it doesn't work. To test the tranny you need to disconnect the secondary winding and measure the AC output on them unloaded. See if you can find the Mercury # and post it here. I have swapped the trannies in the Blonde so yes they will go bad and the power supply is a place to be concerned with but I would get a schemo and go over it and valitify all of the components are what they should be. These are really nice sounding amps for Acoustic when working right and some of the best out there.

[52 Bill]

Mercury was the OEM for SWR transformers, at least before Fender bought them.

Unsolder the secondary leads from the pc board and tape them off. Turn on the amp and see if the transformer still gets hot. Check the voltage on the secondary. Is it right?

If it doesn't get hot, then there is too much current being drawn causing it to get hot. Recheck the circuit board for mistakes and bad parts.

If the transformer is bad, contact Fender. I would assume that a replacement from them will be cheaper than from MM.

[Amp Kat]

Thanks Bill I wasn't aware they ever came with Mercury's and all of the ones I have seen have had SWR gold type laminated EI trannies in them. Maybe it is an older one so thanks for clearing that up.

[J M Fahey]

Mercury Magnetics?
Manufacturers do not believe in Mojo, so MM must have made them in an earlier, more down to earth era.
To be a successsful OEM supplier you must provide good, reliable, trusty products for a very good price.
You do not earn that much per unit, but bulk orders become interesting.

[Appaloosa]

thanks for the tips.

I disconnected the tranny secondary leads. and powered up the tranny and in about 3 min. the tranny did not get hot.

I then put my (-) test lead on the red wire with yellow stripe, and my (+) test lead to one of the plain red wires of the tranny secondary and got 30 VDC. I then switched my (+) test lead to the other red wire of the tranny and got 30 VDC again. is this voltage correct?

Did I test the output voltage correctly? is the red wire with the yellow strip the tranny center tap? their are 3 wires total coming out of the tranny. the tranny is a Mercury Magnetics PT 560015-120.

If i tested this tranny correctly I assume that my tranny is OK? What is the best way to find a short or problem in my board? how do I test the main filter caps? could a cap intalled backwards blow a fuse?

Thanks for all the help, this novice really appreciates its! does anyone know a link to the schematic for this amp?

[J M Fahey]

You identifiwed the leads correctly.
What worries me a little is that you refer to 30V DC while it's AC.
Also you will have to troubleshoot a relatively complex amplifier, for which you do not have a schematic.
Start by asking Fender for it ... and/or google like crazy trying to find it.
Good luck.

[Appaloosa]

thanks, yah for some reason I was thinking one thing and typing another. I will try and find a good schematic and be back.