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Technics SA500, SVITA7129 equalizer Amp IC replacement Ideas?

A

Artopsy

Active Member
I'm thinking the SVITA7129 on the left channel may be bad, in this Technics SA500
the left channel of the phono drops out now and then, unplugging the phono rca for the left channel can fix it for a while. tracing the schematic it leads from rca jack to C401..R403.. SVITA7129 Pin two out of Pin 6 to R409 R411 then C411 ground side is R415
i can test the resistors and caps but if those are not the problem i may need to replace SVITA7129

If it is the SVITA7129 what is the modern equivalent?
these are also in the Technics SA-600, SA-5060, and SA-80
 
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It is a TA7129 - often in Technics service manuals they prefix iCs with SVI - example STK2058IV in manual would appear as SVISTK208IV… same happens with diodes with SVD prefix
 
painttoad said:
i'd check for bad solder joints before buying a chip
Click to expand...
That's exactly how it is acting! I reflower; the IC's, the corresponding resistors, the rca jacks the three wire link from RCA's to the IC area. Deoxed all switches, pots, and rca connectors. checked the resistors near the chip for their ohms, checked some of the caps (maybe more today) and so far all of these are fine. The problem still exists though.

What i have found
if I touch, the left positive rca input with metal (either arcing it, shorting it or grounding it, with me as ground) the channel comes back. If i test for dc current on resistors like R403 or 405 I loose left channel signal.
I no longer think it is the equalizer IC because when the system is working the tone controls are fine. Also there is a youtube video suggesting it could be the tape monitor switch but that isn't it.
When it is working it works for quite a while sometimes; one or two LP's but sometimes it only works for a song or two.
all other inputs are fine.

I don't know enough about electrical to understand why grounding the positive left rca input would jolt the system into full functionality. I can guess I am somehow super charging a capacitor.
My mechanical ocams razor mind want to replace the rca and antenna jacks
 
I've had an SA500 since new. So far all channel loss problems have been switch related. Speaker selector push buttons and tape monitor switches have been the worst. Otherwise I'd agree with @painttoad - cold solder joints. Try flexing the chassis slightly while playing to see if it changes the problem.
 
TPettenati said:
I've had an SA500 since new. So far all channel loss problems have been switch related. Speaker selector push buttons and tape monitor switches have been the worst. Otherwise I'd agree with @painttoad - cold solder joints. Try flexing the chassis slightly while playing to see if it changes the problem.
Click to expand...
I agree, this has been the issue on other amps and receivers, but it is only the left phono input.
Originally there was a horrible distortion on the phono inputs, cleaning and lubing the tape monitor switches and speaker selection buttons then a little reflow fixed the distortion. When the distortion was gone I was able to listen to records, I then noticed the left channel coming and going in the headphones, main speakers and remote speakers.
Two things, that probably have the same effect, temporarily bring the left channel back. 1, unplug the left rca phono input a couple times (creating loud distortion) or tap the lead from the RCA input to the circuit board with a metal object in my hand. I would replace the RCA jacks but in general they are so simple and quite clean i can't see an issue with them.

something is changing in the system while it is on. either a bad solder (I have reflowed 20 or 30 points) a tired part be it a switch or a capacitor.

Also I can not make it fail by flexing the circuit board, wiggling things, flipping switches or turning pots. It has to be simple, just hiding.
 
FOUND IT! :banana:

seems like it was probably the input selector switch. A little deoxit and I mean a little, and some wiggle and It is now on the 5th record with no left channel drop.
Thanks to everyone for your input and putting up with me.

It was so random, I think I got lucky fiddling with knobs long enough and random enough to make it fail.
 
Artopsy said:
FOUND IT! :banana:

seems like it was probably the input selector switch. A little deoxit and I mean a little, and some wiggle and It is now on the 5th record with no left channel drop.
Thanks to everyone for your input and putting up with me.

It was so random, I think I got lucky fiddling with knobs long enough and random enough to make it fail.
Click to expand...
Pretty crazy what a dirty switch can do...
 
Artopsy said:
FOUND IT! :banana:

seems like it was probably the input selector switch. A little deoxit and I mean a little, and some wiggle and It is now on the 5th record with no left channel drop.
Thanks to everyone for your input and putting up with me.

It was so random, I think I got lucky fiddling with knobs long enough and random enough to make it fail.
Click to expand...
I just wanted to thank you... this comment saved me several hours of frustration! I was going crazy trying to figure out whether my problem was with my turntable or my SA200, and it appears it was the input selector switch! Deoxit to the rescue!
 
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