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My Amp is Broken - Not Sure What to Do - Any Recommendations?

I went to turn on my Audio Research SD135 amplifier the other day, but it will not turn on. According to the Audio Research service technician I spoke to, the problem is a broken Thermal Trak module chip. He said that it is a temperature sensing component, and that replacements are no longer being manufactured. He said that it is a known problem, and that Audio Research will give me credit to purchase an Audio Research amplifier from an Audio Research authorized dealer. 

I was wondering if Audio Research makes anything powerful enough to drive Vandersteen 3A Signature speakers (which need between 100 - 200 watts of power)? I am using an Audio Research SP8 Mk II as a pre-amp.

I don't really have much of a budget and am not sure what to do. I would appreciate any advice. Thank you.
distortions
johnsonwu
469 posts
 
https://www.mouser.com/ProductDetail/ON-Semiconductor/NJL3281DG?qs=sGAEpiMZZMvFp%252byPHbnZYyVkaBWrH...

3281D was INDEED obsolete.
Original collateral dated June 2006
http://www.onsemi.com/pub/Collateral/NJL3281D-D.PDF

replaced by 3281DG  Same application notes per Mouser.com and ONSemi.  Available and NOT discontinued.

My HD220 has not blown (yet) so I have not attempted a repair myself.
I suspect it means you need to change out ALL the devices for matching sake.  That's likely why Audio Research doesnt want to deal with it.
Boy if they could just respond to my email and get me the schematic!
rodman99999
6,158 posts
 
It was my experience, that William Z Johnson cared very much, about his customers and his corporation. On the other hand; I’ve no doubt Macintosh wishes the corporation(and the competition) never existed, though they now own it.
johnsonwu
469 posts
 
OP lucky you the schematic is HERE:

https://elektrotanya.com/PREVIEWS/63463243/23432455/audio-research/audio-research_sd135_amplifier_sc...

I bet not everything is toast likely 1 phase of 1 channel.

Get a tech WHO KNOWS HOW TO MATCH OUTPUT DEVICES.
Buy a dozen of 
NJL3281DG (NPN) NJL1302DG (PNP)
and match them and repair the blown channel!


johnsonwu
469 posts
 
Even the manual found online says the original devices are 3281D and 1302D
Replace the defective channel's output devices with MATCHED
DG versions and you are good to go.

atmasphere's avatar
atmasphere
11,837 posts
 
Hm, The output section is right out of OnSemi's application notes.

Devices like this give me the willies, since so much relies on them. If it were me, I would be tempted to test the transistor portions to see if they are still good, and if so, perhaps see if a diode applied the transistor could sub for the diode portion of the device. If the amp heats up or has crossover/notch distortion issues, then a bias scheme would have to be employed.
But of course outfitting it with new devices seems the preferred method. This just doesn't seem like it would be that hard to sort out.
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