Sony STR-V35 receiver won't come out of protection - WEIRD

[leesonic]

I have a Sony STR-V35 receiver that won't come out of protection. The weird thing is, both the bias and DC offsets test fine. I actually tried adjusting them, and I got the offset as near to zero as I could, and the bias set at 20mV, as per the service manual.

There is around 38v on both sides of the relay coil, and grounding the one side that goes to Q616 makes it click in. I should add that I did this after pulling and testing Q616. It almost seems like there is something wrong in the protection circuitry that is causing the problem. I did remove and test all the transistors in this circuit, they all tested fine. With Q414 removed, the protection relay clicks in.

Something else seems strange. See all those components with the red lines though them? They aren't installed on the board on my receiver. It doesn't look like anyone has been in there before and removed them. Maybe the Sony designers realized they didn't need them? The inputs marked 1-2-3 and 4-5-6 are taken from each emitter resistor and it's common ground.

I did measure a whole bunch of voltages, but I lost the paper so I'll have to do it all over again.

Lee.

 

[Robisme]

I'd replace C610,611, and 612 and see what happens.

Rob

 

[Jon_Logan]

Look around for some glue that was used to hold down the larger caps.

I've gone through this weirdness on a couple of Sony's of that vintage where the glue turns conductive and it causes enough leakage current to swamp out the high impedance portions of the protection circuit.

Check the DC voltage at the Base of Q-615.

 

[leesonic]

Look around for some glue that was used to hold down the larger caps.

I've gone through this weirdness on a couple of Sony's of that vintage where the glue turns conductive and it causes enough leakage current to swamp out the high impedance portions of the protection circuit.

Check the DC voltage at the Base of Q-615.

I saw that stuff, it's pretty spread out around the main caps, enough to corrode a few jumper wires around there. There were also some solder connections on these jumper wires where the corrosion had spread through to the other side. I cleaned up the connections and re-flowed the solder, maybe I will pull the main caps out and give it a GOOD clean up. I had no idea it could turn conductive.

Can you recommend anything to clean this glue? I know the rubbery glue on Pioneer and other brands can be softened and then cleaned with acetone.

Lee.

 

[lalomarantz]

I greet with great pleasure

i have the STR-V35 , it was the same problem that yours, protection relay will not activate if protection circuit detects DC voltaje at output of power amplifier, you should test DC voltaje at amplifier output before relay, you should put voltmeter´s test probe to one side of the output coils L601 and L651, reading voltaje must be 0V within +/- 100mV, if DC voltaje is greater than the above figures, protection circuit will prevent relay activation, transistors shorted or leaking are the cause of DC output voltage of the amplifier, in my case i found Q602 shorted, Q606 shorted, Q604 Shorted, R619 and R614 open. the failure was produced by output transistors overheating, caused by high bias value adjustment, service manual indicates 20mV, it was corrected to 10mV.

the missing parts of protection circuit are the same of my STR-V35, do not worry about them,

 

[avionic]

C612,C615,D805,Q615,616---:scratch2:
What voltage do you have a the base of Q615.

 

[lalomarantz]

voltages of Q615 on my STR-V35 normally operating are: Base 1.48V , Collector 0.87V , Emitter 0.8V

voltages of Q614 are: Base -38.8V , Collector 1.47V , Emitter -39V

voltages of Q616 are: Base 0.8V , Collector 0.08V , Emitter 0V

voltages of Q612 are: Base 0v , Collector 1.48V , Emitter 0V

voltages of Q613 are: Base 0V , Collector 1.48V , Emitter 0V

all voltages were taken two times for confirmation


missing parts of my V35 are: C614,C664, R643,R693,D606,D656, Q617, Q667

Q611 and Q661 are 2SA970 instead 2SA1049 , i think that are production changes for improvement

 

[leesonic]

I desoldered the two main caps today, and a couple of other components that were coated in the old glue. With these clear, I cleaned the board by applying some acetone with a cotton bud (Q-tip) and then scraping it away with a small flat bladed screwdriver. After reinstalling the components, it came out of protection - hooray!

I also disassembled the speaker/power switch to repair the power switch part. If you remove the mounting bracket, there are four little tabs that hold the shaft. Bend these straight, and you can pry off the front bushing and remove the shaft from the switches. After this, there are four more tabs that hold the power switch in, bend these back and remove it. Mind had burned contacts which I cleaned with some 400 grit sandpaper. When I reinstalled it, I added a capacitor across the terminals that will hopefully reduce the amount of arcing across these terminals.

Now all I have to do is fix the blown lights on some of the input selectors. I'm thinking green LEDs...

Lee.

 

[petehall347]

voltages of Q615 on my STR-V35 normally operating are: Base 1.48V , Collector 0.87V , Emitter 0.8V

voltages of Q614 are: Base -38.8V , Collector 1.47V , Emitter -39V

voltages of Q616 are: Base 0.8V , Collector 0.08V , Emitter 0V

voltages of Q612 are: Base 0v , Collector 1.48V , Emitter 0V

voltages of Q613 are: Base 0V , Collector 1.48V , Emitter 0V

all voltages were taken two times for confirmation


missing parts of my V35 are: C614,C664, R643,R693,D606,D656, Q617, Q667

Q611 and Q661 are 2SA970 instead 2SA1049 , i think that are production changes for improvement

have you got 38v at relay coil ?

 

[lalomarantz]

the measured voltage in the relay coil is 25.6V

 

[petehall347]

looks like relay ought to be clicking in ..that's as long as the voltage is only on one side of the coil .

 

[orsen]

i have one of these amps also.... picked from good will for $5
when i got it home it powered on and showed the fm worked but no output.
it went in the closet for months, until today.

i took it apart and it is full of corrosion all the wire jumpers on the boards are rusted, no sound. no continuity, no relay click.
after lots of cleaning i have it all working
except the light for FM switch
except i cant play speakers A + B
A works
B works
but not A + B
any ideas?

what size was used to switch the lights to led?

thanks for any help

 

[Montycat]

Yup, an old thread but I just got an STR-V35 back to tolerable working condition. One channel was intermittently not coming on. Tapping the relay seemed to make it come back, or even occasionally switch sides. I thought maybe cold solder joints so I reflowed the ones at the relay and in the neighbourhood. I also removed the 2 large power supply caps and cleaned up the glue. Yup, the jumper wires in the vicinity were corroded. Once it was back together it still did the same thing.

At this point I sprayed contact cleaner into the relay and manipulated the arm inside. NOW it works!

Next time, or if it gets flakey right away, I might replace the relay but for now it seems ok.

 

[Montycat]

It got flakey.

So, not having an all-night relay store nearby, i took it out of circuit, disassembled it and cleaned the contacts. Now with it soldered back in, it works.

If that doesn't last, I might just solder some bridges across the contacts. This rig owes me nothing.



Dirty black contact pads



Contacts cleaned with 800 wet/dry paper



Soldered in again.

 

[Robertmcc]

I recently got one of these from Goodwill. The right channel through speakers sounds distorted, but works perfectly with headphones plugged in and the speaker selector set to off. I put it on A (with headphones still plugged in)I get distorted sound out of the right channel both out of the right speaker and in the headphones. What should I be looking at to fix? Any help would be greatly appreciated

 

[llwhtt]

The right channel output stage is possibly bad. Headphones don't use very much current and the driver stage, Q656/657, is able to supply enough. Speakers demand more current and the driver stage is not able to supply it hence the distortion. Possibly Q654 and Q658 are bad along with some supporting components. Another possibility is a dirty/bad speaker relay, RY601.

Craig