Another 40 year old Technics Amp repair - (if possible)

Thread Starter

Alex H

Joined Jan 13, 2023
3
Hi

I have a 40 year old Technics SU-VX500 that I've been using all that time, most recently as part of a home cinema setup.

We noticed a few days ago that there appeared to a problem with the sound output, so I did a little bit of investigation.

The problem appears to be concerned with the balance of the speakers. i.e there is no sound to the LHS speaker at all, even with the control turned all the way round.

Swapped the speakers and their cables over and the fault remains.

Somewhere along the line I changed changed tack slightly and discovered another vital piece of information.

If I use input via AUX (from my laptop) the LHS speaker does not function

If I use input from the Technics Tuner that I still have (tuner input on the amp) the RHS speaker does not function.

From the schematic I have the balance control is only a variable resistor affecting the sound signal.

I'm reluctant to bin the amp for such a simple (?) problem, so any help would be gratefully received.

Regards

Alex
 

abrsvc

Joined Jun 16, 2018
138
I need to locate the manual for this one, but I would first look at the switching IC. These are common faults. The IC will be either a TCxxxx or LCxxxx. I don't recall the specific IC. I will update this once I locate the service manual (paper).
Dan
 

abrsvc

Joined Jun 16, 2018
138
I stand corrected. I found the service manual (see link below) and a quick search shows that this unit has a mechanical switch for the input selector. I would first clean this switch. The moving side that is failing suggests that this rotating switch has some dirt or corrosion on it thus the moving defective side. Use a switch cleaning solution and "work" the switch. Otherwise, try cleaning the pads with a burnishing brush to get them shiny.

Manual link: https://elektrotanya.com/technics_su-vx500_sm.pdf/download.html

Dan
 

Dodgydave

Joined Jun 22, 2012
11,303
That sounds like the input select switch, looking at the circuit diagram, its a rotary type put some switch cleaner on it and give it a clean.

Screenshot_2023-01-13-17-32-48-274_com.adobe.reader.jpg
 

Thread Starter

Alex H

Joined Jan 13, 2023
3
Thanks all for the quick replies - I'll give it a go when I can get some cleaning stuff and let you know

regards

alex
 

KeithWalker

Joined Jul 10, 2017
3,096
When you are cleaning the switch, check for bent contacts. If you don't have switch cleaner, isopropyl alcohol with a little bit of petroleum jelly (Vaseline) dissolved in it will work. Apply it with a Q-tip.
 
Last edited:

Thread Starter

Alex H

Joined Jan 13, 2023
3
Thanks for all the replies.

I bought some switch cleaner spray and managed to get it into the switch on both sides without taking too much apart.

The amp is working as it should now and has improved the sound on my games PC no end

Regards

Alex
 
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