Phonoland

I have been working on my amp for now sound, and i seem to lose the audio at Q 5106 & Q 5101, i replaced them with new transistors (ecg128) but that didn't seem to correct it, I then put in a different set of seeburg 309686 (that i had orginaly pulled from a different spot on the board because i thought they were bad.) they worked for a few seconds and then died.
Any idea as to what might be causing them to keep going:?:

Thank you
David

If these are the audio output transistors, check the driver transistors just ahead of them. Often a failed output transistor damages the driver, which then fries every output transistor replacement.

Bad, shorted, or missing speaker connections can damage most transistor amps.

One other thing to look for in amps from the 1970s is a biasing diode (or a pair of biasing diodes) between the bases of the transistors. Failure of this can cause both transistors to turn full on at the same time, causing too much current to flow through the output transistors.

these are the first transistors, on the preamp
i have the schematic posted on my site so you can see the transistors i am talking about.

http://www.itsmecam.net/public/gallery/ ... preamp.jpg

are cr5101 &5102 the diodes you are refering to?

This sounds very much like your SOS circuit is tripping. Check the cathodes of CR5101 and CR5102. If they are negative, the SOS has tripped. Confirm by shorting pins 7 and 11 of relay K5101 together. If you now get audio, the problem is that the SOS tripped.

Cheers,

Tony Miller

thanks tony that did the trick. I'm curious if that was the problem on the original amp? if i recall it did the same thing.

but now it's back to playing what ever it feels like playing, (it has a new ground wire on it as per your suggestion a few months ago wich took care of the problem that time. only difference is it's spotty on where it stops, other than on every record.

i'm almost ready to give up on the thing...

took a min for the brain to kick in (been a long day) but once it did, rememberd a few other posts, so decided to run a new cable from the tormat to the dcc controller, and now it seems to be playing fine with no extra selections.

Now just a few more things and she will hopefully run almost like new (knocks on wood)

thanks for all the help Tony

David

I did not mean to permanently short the relay contacts as that will disable the SOS circuit. If, with the contacts NOT shorted, it continually trips, you should determine what is causing the trip condition.

Cheers,

Tony Miller

nope didn't perminantly short it, just touched the 2 together, i noticed if i turn the volume up to far it will cut out. Although a couple things that i noticed on the amp is the driver board does not quite match the schematic that i have.

When I got this current amp I also had to replace Q 115, 116, 117, and 118, all four were bad, it's aslo had an almost complete re-cap except for the ones i can't find. the two 1500 uF N.P lytics on the out put.

i'm also getting alot of distortion on one channel, will check that tonight when i get home from work, good chance it's comming from my preamp board.

thanks
David