Technics SA-DX950 intermitently sounds blown out

Hi!

The F70 error certainly indicates a blown fuse inside.
The real problem is why the fuse is blown: there are only two possible reasons
1. there is a short circuit on the output (lines or speakers)
2. you have a blown output transistor (and that means some work and skills to replace).


To be sure, please change the fuse with a same rated fuse (buy more than one because it can blow again). Disconnect the speakers and turn the amp on. If the fuse blows again, it is sure something wrong with the output transistors. If the fuse remains ok, then please check all the wiring to the speakers.

Hope it helped.

Regards,

Bogdan

problem is oxidation...Remove and clean the ends of cables with sandpaper slowly...there is slim and flat cable into the reciver (together with five cable)...specially remove it's socket and clean it...

For the question at the top you most likely blew your computer chip on the Technics sa 810, we have 2 of these receivers and one lost it left channel and the green auto light went out, we have taken it to several places and they ended up having to turn down the power. now it is working great sounds the same just needs more volume level, but it ended up costing $500 CAD, you can't get the auto to work any more, you will most likely need a new stereo, The Technics SA 810 is an awesome receiver, good luck fixing it

Check if a or b or what is reflected for speaker.

A couple of possibilities: Bad solder on power regulators (attached to main heat sink) or cooling fan may not be turning on when volume is raised.

This may sound like a silly check, but verify that the tape monitor switch is not engaged. What is the quality of the sound when turned up? Is the cound clear or raspy?

Thanks,
Dan

The most likely culprit here is the output protection relay. The contacts are a little corroded and the higher volume "jumps the gap" temporarily "cleaning" the contacts. The relay should be changed. I don't have the manual with me, but the following relays are in the unit. One of them is the speaker relay:

Part # Cost
RSY0054-C $12.63
RSY0040M-0 $ 5.89
K6B2AHA00014 $ 8.14


Dan

sounds like the speaker protection relay is operating probably from a dc condition appearing on power amplifiers outputs. probable cause is dry solder joints to the output stages. will need some reworking of the PA stage soldering to fix.

you have a short circuit occurring in speaker outputs. If you are using the high power inputs of the sub, try disconnecting them first. check polarity of speaker connections to sub also.

when turn on receiver , after few seconds got message
F70. when wants to do any operation with receiver got message SWITCH POWER OFF