Rickenbacker TR75 GT blows fuses

perkan · Post by **perkan** » Wed Sep 28, 2005 6:30 am

I bought a broken TR75GT in hope that I could fix it, but since it blows the fuses that leads to the power amp, I can't measure anything with my multimeter.

I have replaced the electrolytics, most of the transistors and the 5W resistors. I have checked that the rectifier (AC to DC right?) works. It gives about 48DCV.

Is there anyone who knows if this is typical problem with this model? Somebody got an idea how to fix this problem?

I've heard that you can replace the fuses temporarily with 5W resistors (don't remember how many ohms) and check if one ore more of the transistors get warm.

Schematics: www.rickenbacker.com/pdfs/19345.pdf

Thanks!

jingle_jangle · Post by **jingle_jangle** » Wed Sep 28, 2005 8:39 am

Have you checked the power transformer windings for continuity? Sounds like bad windings to me.

aoresteen · Post by **aoresteen** » Fri Jan 13, 2006 3:27 pm

Erick,

You need a current limiter to figure out what's going on.

Kendrick sells one for $100

http://kendrick-amplifiers.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=KOS&Product_Code=KEN04-limiter&Category_Code=04

Good luck!

Tony

jingle_jangle · Post by **jingle_jangle** » Fri Jan 13, 2006 4:15 pm

When I first plugged in my Rick PA-120 4-channel amp, it did the same. Went over the whole thing with a multimeter, checking for shorted windings, bad this and that...

After two hours of mounting frustration, it was the power cord!

tracy · Post by **tracy** » Mon Apr 10, 2006 11:07 pm

I've worked on several of these over the years and invariably it's power transistors as well as associated circuitry that gets dragged down when the output starts pulling hard to one side. You have to check EVERYTHING and then bring it back up patiently, first with the output transistors out of the circuit, NO LOAD, to see if the feedback is working and that there is little if any DC at the output. Otherwise, when you fire it up, it'll take out your new components along with a little fire & brimstone for your amusement. A nervewracking endeavor. Not for the squeamish.

admin · Post by **admin** » Tue Apr 11, 2006 2:16 am

Tracy: It is really nice to see your post. Your comments are much appreciated. Can you comment on the working relationship between Road and Rickenbacker?