No sound from Technics SA-8500X

[RockaMarka88]

Hi, everyone.

A few days ago I acquired a Technics SA-8500X four channel receiver. It is in beautiful cosmetic condition and performed pretty well until now…

It powers up fine and all the lights illuminate, but after about 10 mins into a record, some loud static noise comes from the rear left speaker, then all sound disappears. Whether in FM, Phono or Aux mode, no sound comes from any of the speakers.

Any ideas what this could be?

Many thanks,

Mark.

 

[DuncanS]

I'm assuming it is repeatable, so if you turn off wait a while and turn back on it plays for 10 mins. My suspicion is a failing Electrolytic Capacitor, probably in the rear left amp (but not necessarily) which is going 'short' and causing the receiver power supply output to collapse.

 

[kfbkfb]

I don't have any troubleshooting info, however...

"The SA-8500X - first 4-channel receiver with automatic CD-4 separation"

Once it's working, please try out this CD-4 automatic separation system and, if possible, post some graphs (made w/PC software) showing the resulting separation.


Kirk Bayne

 

[RockaMarka88]

Watch the video I've attached below to see what happens when I switch the unit on...

For about three seconds there is sound, but there is also loud static and the front left VU meter goes completely haywire. This is followed by a click and all sound is lost completely. I'm assuming this is the protective relay system kicking in?

I've had a look inside the receiver and tested fuses, resistors e.t.c. with a multimeter, but their readings all came back normal. Even a 4.7 ohm resistor on the power board that looked damaged read as 4.7 ohms.

Could the culprit be something much simpler, like wrong speaker wire? Should I be using low capacitance wire? I have four Wharfedale 3XP speakers in each corner of a 5m x 2m room...



Any help would be greatly received.

 

[DuncanS]

No the speaker cable will not affect anything. There is mains hum, then the crackling sound, then nothing, unfortunately this is most likely internal to the amp. Because it it is affecting all channels (no sound from any) probably Power Amp stage power supply related.

 

[RockaMarka88]

No the speaker cable will not affect anything. There is mains hum, then the crackling sound, then nothing, unfortunately this is most likely internal to the amp. Because it it is affecting all channels (no sound from any) probably Power Amp stage power supply related.

Thanks, DuncanS.

Funnily enough, I checked the power supply board and saw a 4.7 ohm resistor which looked damaged. I was convinced this was the culprit, but when I tested it with a multimeter, it came back as 4.7. Should it still be replaced even if it has a satisfactory reading?

 

[DuncanS]

Thanks, DuncanS.

Funnily enough, I checked the power supply board and saw a 4.7 ohm resistor which looked damaged. I was convinced this was the culprit, but when I tested it with a multimeter, it came back as 4.7. Should it still be replaced even if it has a satisfactory reading?

View attachment 69692View attachment 69694View attachment 69695

No I wouldn't (sent you a PM with some manuals I found on-line). I'd check if you get a +/-34V on the amp power supply.

 

[Doug G.]

You should heat that resistor up as you measure it and wiggle it around. See if your reading stays steady. If it does, no need to replace it now but I would eventually. I mean, that resistor may be totally unrelated to your problem but, just as a matter of principle.

As Duncan suggested, look at the rail voltages and monitor them as the problem occurs.

Doug

 

[RockaMarka88]

No I wouldn't (sent you a PM with some manuals I found on-line). I'd check if you get a +/-34V on the amp power supply.
View attachment 69697

Okay, how do I do this?

Where do I put the multimeter rods to test the voltage?

 

[DuncanS]

Best to look at page 18 of the Service Manual in the PM I sent to get a clearer view and when you down load the files you can print the pages.

The PCB layout of the Main Amplifier Circuit Board is shown along with the test. Look between points E & C on TR607 for the positive +34V, and E & C on TR608 for the -33.7V negative supply. There are 4 identical boards for the channels, so the same test point positions on any of those 4 will show you if the voltage is present, or disappears a few seconds after power on. BTW I don't think this is something you will be able to easily fix yourself.

 

[RockaMarka88]

Best to look at page 18 of the Service Manual in the PM I sent to get a clearer view and when you down load the files you can print the pages.

The PCB layout of the Main Amplifier Circuit Board is shown along with the test. Look between points E & C on TR607 for the positive +34V, and E & C on TR608 for the -33.7V negative supply. There are 4 identical boards for the channels, so the same test point positions on any of those 4 will show you if the voltage is present, or disappears a few seconds after power on. BTW I don't think this is something you will be able to easily fix yourself.
View attachment 69699

Thank you very much for your help, DuncanS.

I’ve already found the Service Manual on hifiengine; I couldn’t make head nor tail of it!

I think I’ll do what I should’ve done in the first place and just take it to a repair shop! Thinking I could fix it myself was a bit overambitious!

 

[Soundfield]

I think I’ll do what I should’ve done in the first place and just take it to a repair shop!

Good luck finding a local repair shop in the UK - they more or less died out decades ago.

 

[MidiMagic]

The resistor could read normal when no voltage is on it, yet not properly pass current.

 

[DuncanS]

Good luck finding a local repair shop in the UK - they more or less died out decades ago.

I suspect that an on-line search will be the way to go to find someone to fix the Technics.

I was lucky I found a really good Reel-to-Reel service/repairer on line: Servicesound, reel to reel tape recorder & valve amplifier repairs. I found another to service my portable DAT Sony DAT recorder repair service (andyselectronicstuff.co.uk), but no luck on cassette recorders. Yes I like obsolete media machines!