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Louie
Louie, Technician
Category: Consumer Electronics
Satisfied Customers: 12163
Experience:  25+ yrs. experience in the field and 5+ yrs. online, down to component level.
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Aric...I've got a Technics SA-DA15 with the displayed

Customer Question

Hi Aric...I've got a Technics SA-DA15 with the displayed "Overload" problem...no speakers attached. I've got a service manual but it has no theory and no troubleshooting guide. I'm a retired tech/eng with over 40 years experience and I'd like to try and save the AV amp. I have some test equip. None of the obvious fuses are blown and the receiver was working fine for years with the same setup (no recent changes). Can you help?
Submitted: 1 year ago.
Category: Consumer Electronics
Expert:  Louie replied 1 year ago.

Hi and welcome to JustAnswer,

Thank you for the question and your patience. With the indulgence of Aric and should you still need assistance for information purposes only...

Initially, have you tried checking the base-collector-emitter resistances of the output transistors? ...forward & reverse?

Can you also please try uploading the Service Manual to any of the free hosting sites? dropbox or mediafire

Customer: replied 1 year ago.
Not yet...I was looking for Technics-model-specific info for this AV amp. An Internet review showed me that the fail mode has occurred to quite a few people with Technics amps and some fixed it by just reflowing the fan connections. I was hoping you'd point me to a Technics Theory of Operation or Troubleshooting guide that would tell me what conditions (along with blown output amps) could lead to the "overload" display. Your answer is a good general one, but not the more comprehensive here's-how-the-overload-circuit-works one specific to this model I was hoping for. I'm disappointed, but I'll cough up the $21 I must pay now and proceed on my own from here.
Expert:  Louie replied 1 year ago.

Appreciate the post back.

If it were a fan issue, then it would be a temperature concern. The description of "...displayed "Overload" problem ..." would imply that the speakers and/or its wires have shorted causing high current flow on any of the output transistor pairs. However, since ther are "...no speakers..." connected, then the primary suspect would be any of the transistors thus the above post.

The request fro the SM was to have a common reference when exchanging information particularly on test-points.

Theory of operation can then be provided based on the particular section that would be checked.