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Technics SU-V505 Channel problem

T

Tenknits

New Member
Hello all!

I have a Technics SU-V505 and I've had an intermittent problem for quite a while that seems to be getting worse.

It started going quiet with one channel. This was resolved by turning the input selector around and that usually did the trick. Sometimes turning the speakers off and on again would work. Worst case scenario - power off and on again. It was pretty rare so I didn't worry too much.

Now it's becoming a real drag and often isn't fixed by any of those things.

I used contact cleaner in the pots and that seemed to do the job for a bit, but now it's back and the cleaner isn't fixing anything.

Looking more closely I noticed that the 'bias' lamps don't come on when the amp is started up anymore. I read somewhere that these bulbs operating is critical to the amp itself working effectively... could this be the problem? Two bulbs are off : the bias lamp and the 'computer drive' lamp.

The guy I got this from told me that the lamps had been changed recently, if so I wonder if there is an underlying problem that is causing them to blow...

I also read in this thread (https://audiokarma.org/forums/index.php?threads/technics-su-v505-problem.298040/) someone had a similar problem solved by resoldering the speaker relay.

Perhaps resoldering the relay will fix the issue? Could the bulb even be not lighting up because the relay solder is bad?

Any help much appreciated! (inc. any pictures to point out where the speaker relay is!!) :))
 
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The bulbs are an easy fix and something you can easily do yourself. Here is a thread that I found. But I also modified the procedure so that I did not have to desolder the LEDs. I just cut the plastic shroud in half at the right place revealing the bulbs and then it was an easy desolder and resolder job with new lamps...
https://audiokarma.org/forums/index...vxxx-new-class-a-computer-drive-lamps.779067/

I don't think that has anything to do with the channel issue however.
 
You want to do some diagnosis before blindly replacing things. Tap on the speaker relay and see if that makes a channel come on. Use something non-conductive like wood when you do that. Also sometimes a speaker realy will kick in with a quick turn of the volume knob. But there are ways to diagnose before a shotgun replacement strategy.
 
When you used contact cleaner in the pots did you also leave some sort of lubricant for protection? Some cleaners do have some protectant in them.
 
coonmanx said:
You want to do some diagnosis before blindly replacing things. Tap on the speaker relay and see if that makes a channel come on. Use something non-conductive like wood when you do that. Also sometimes a speaker realy will kick in with a quick turn of the volume knob. But there are ways to diagnose before a shotgun replacement strategy.
Click to expand...
Good advice. The bulb needs replacing so I'll get to that when the bulbs arrive.

I saw your great contributions to a really helpful thread. I'll see when I get to it whether I want to unsolder the leds or just do your modified technique. Nostalgic part of me doesn't want to cut anything, but I'm probably being sentimental!

My plan is to remove and clean the speaker relay, that might solve the issue.

Problem with a systematic approach at the moment is that the fault is intermittent. There are two things that seem to get the channel back - the input selector and the speaker select switch. Fiddling with these on and off I can usually get it working again. I haven't managed to access the speaker select switch with contact cleaner, so I'll try tomorrow when I look at the relay.

Thanks for your reply and great help @coonmax
 
So just now one of the channels stopped working, I flipped the select switches and the other channel started working, then by turning the speakers off and back on I now have both channels working. My hunch is it's the relay - needs a good clean.
 
Tenknits said:
https://www.nortonline.com.gr/norto...ner-clover-color-without-lubricant-400ml.html

This is the cleaner I have, it's without lubricant
Click to expand...
After cleaning you want to leave some lube in there. Otherwise the issue can happen again. Some members here like to finish with Faderlube. I just use something that contains a lubricant.

If the problem happens again I would pop the lid on the unit and locate the speaker relay and then tap on it and see if there is any change.

These are really great amps. I own the SU-V707. As far as cutting or not cutting that plastic shroud that goes around the bulbs, that shroud can not be seen. It is behind the faceplate and nobody will ever know and it will function exactly the same. But if you want to spend time desoldering and resoldering that is up to you. I wasn't going to waste my time and effort on something like that where nobody will ever know the difference.
 
The speaker selector switch is basically a screw drive in front and then a slider switch in the rear where the actual contacts are. I know this because the SU-V707 that I bought "for parts or repair" had a broken speaker selector switch. I fixed it by mating the front half of a different switch to the rear part of the switch that was in there. And now that works.
 
Just read through your thread. Fantastically informative, thank you! Also inspiring as you clearly weren't an 'expert' at these things at the beginning and persevered and succeeded! Which I suppose makes you an expert! Inspiring for me whose knowledge of electronics is pretty basic.
 
I cleaned the relay today. So far no channel cut out... time will tell (problem was intermittent before). Bulbs on order. :beerchug:
 
Yeah, sadly that didn't fix the problem! I moved, put amp in storage for a while and then used it at a neighbours for a film night and the speakers kept cutting out to the point where we gave up and used a bluetooth speaker. Disappointing.
coonmanx said:
The bulbs are an easy fix and something you can easily do yourself. Here is a thread that I found. But I also modified the procedure so that I did not have to desolder the LEDs. I just cut the plastic shroud in half at the right place revealing the bulbs and then it was an easy desolder and resolder job with new lamps...
https://audiokarma.org/forums/index...vxxx-new-class-a-computer-drive-lamps.779067/

I don't think that has anything to do with the channel issue however.
Click to expand...
Yup I managed to replace these without cutting anything. They all work great. Speaker channel issue persists however... sigh.

My thoughts are to either replace the relay and see whether that resolves the issue. However I cannot find a replacement for the model (Matsushita 6A60V AC JD2-H-DC24V-Y4 AJD6910) perhaps there's a substitue that has the same leg position and would work?
Does anyone know whether there is a viable alternative for this relay? I suspect that someone is making and equivalent with a different code/ brand etc.

Other thoughts are to get it up and working without the cover on and tap the relay when it cuts out to see if it fixes it. At least that way I define the problem (coonmanx suggested this).

Or perhaps I should just open it up and heat up the solder joints on the relay and see if that resolves it as it seems to have done on this thread: https://audiokarma.org/forums/index.php?threads/technics-su-v505-problem.298040/

20241018_150342.jpg
 
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