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Technics SU-C01 beautiful circuit board - how to fix input selector

BadAudioAdvice

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Based on the measurements printed on the case, seems like this offers SOTA performance ;)

The only problem is that the input select isn't behaving nicely. I need to position it in-between inputs, otherwise the Left channel is very distorted (sometimes it works OK in the actual position, but usually not).

I was thinking that it would be a quick fix with some Deoxit, but I'm not at all familiar with how they implemented the selector switch.

Also, when taking off the bottom, I was struck by how beautiful IMO the circuit board is, the tidy wiring, layout, and the labelling on the circuit board.

Any advice appreciated, and enjoy the pics!
 

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Had a look into the service manual. The input selector switch is a sliding type where it is probably not easy to reach the contact surfaces due to closed design, although I have no picture of it. Hard to get it good again. If possible to buy a new one (which might be impossible due to age) is the best.
What I would do is to use WD40 spraying it into the switch assembly. Then turn the selector switch at least 20 times. Try it with an audio signal whether it is OK now. If not, more WD40 and again many times switching. When good, then get the WD40 out by spraying isopropanol alcohol into it until clean. Then let it dry. Also between the switch and the PC board needs cleaning. Alternative cleaner is automotive brake cleaner, but needs to be used in outside air.
 
Thank you for your response!

Yes, the selector switch is a very interesting mechanism. As one rotates the input selector knob, it engages with teeth which slides the selector mechanism.

IMG_0712.jpeg


I just filmed a quick video of it in action:


What is your thought on WD40 vs Deoxit? I have Deoxit on hand, but not WD40, and a quick Google shows that opinions are certainly mixed when it comes to the use of WD40 in electronics.
 
Thank you for your response!

Yes, the selector switch is a very interesting mechanism. As one rotates the input selector knob, it engages with teeth which slides the selector mechanism.

View attachment 352288

I just filmed a quick video of it in action:



What is your thought on WD40 vs Deoxit? I have Deoxit on hand, but not WD40, and a quick Google shows that opinions are certainly mixed when it comes to the use of WD40 in electronics.
Thanks for the pictures. Well, I never used Deoxit and of course it may work. Perhaps it is necessary really to reach the contacts with Deoxit.
On a lot of audio vintage gear I used always the WD40 and it was all OK. But as I wrote it needs to be removed by cleaning. If possible, after cleaning using a vaseline spray may help to keep the contacts longer good. One spray which can be left is Ballistol (originally used to clean and lubricate weapons, and it has a not nice smell) which is available here in Germany. Don't know whether it is available at your location?
 
I was also thinking that I could use CRC Electrical Contact cleaner.

I've never repaired any vintage equipment before, and most of the videos I saw online recommended Deoxit, but that was usually for POTS.

This input selector seems like it has discrete connections on the bottom, and a bridging contact, since I can get a cleaner connection mid-way between inputs, before it switches to the next input.
 
What is your thought on WD40 vs Deoxit? I have Deoxit on hand, but not WD40
I absolutely would not use WD40 in HiFi equipment (not even the WD40 contact cleaner).

Either use Deoxit or Servisol Super 10 (now also known as Kontakt (Servisol)Super 10 Switch Cleaner)

In the case of that switch, it could be removed from the PCB and very carefully dismantled, cleaned and reassembled (assuming it's not physically broken - the plastic does sometimes crack with age).

If you're not a tech yourself, I'd be inclined to find a competent tech who can fix it for you, but dismantling it is a long job...
 
I absolutely would not use WD40 in HiFi equipment (not even the WD40 contact cleaner).

Either use Deoxit or Servisol Super 10 (now also known as Kontakt (Servisol)Super 10 Switch Cleaner)

In the case of that switch, it could be removed from the PCB and very carefully dismantled, cleaned and reassembled (assuming it's not physically broken - the plastic does sometimes crack with age).

If you're not a tech yourself, I'd be inclined to find a competent tech who can fix it for you, but dismantling it is a long job...
Why would you not use WD40 in HiFi gear?
 
assuming it's not physically broken

It appears to be in fine condition based on feel, response to rotation of the knob, and from as much as I can see when it moves (the view in the video I posted is about as much as can be seen).
 
You have not mentioned which type of "Deoxit" you have.
There is D series, which is cleaner.
There is G series, which is preservative.

In the D series alone there are at least 3 different formations...

Either may help.

I have both and in these situations I "follow the directions" and clean with D series first, then follow up with G series.
If you only have G, what is typically referred to as Deoxit Gold, you just may have to use more of it to achieve cleaning action.

I had the exact same problem with a Yamaha receiver using the sliding selector switch type. Deoxit helped but not permanently.
The contact surfaces may just be too worn out to make reliable connections.

I would not use WD-40 on electronics because what you are try to accomplish is not the intended purpose of the product.
Not to mention it being highly flammable.
It may anecdotally "work" in some situations where something is better than nothing. But there are better products intended
specifically for electrical contacts.
 
Also, when taking off the bottom, I was struck by how beautiful IMO the circuit board is, the tidy wiring, layout, and the labelling on the circuit board.
That board reminds me of when I was first year apprentice at the big board learning to use drafting pens with stencils. The stencils had oblique lettering that looked just like on this PCB. While we were doing our time in that class room, the teacher (who also taught us bridge, poker and Diplomacy) got his first Rotring electronic lettering machine. It mounted on the drafting board arm, a bit bigger than a large pocket calculator, and took Rotring pen without the handle.

Memories evoked by a photo of a preamp PCB.
 
While you're at it, PLEASE clean all those pretty gold, RCA ground shells. Then also do your best to clean the connection inside each one...:)
 
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PLEASE clean all those pretty gold, RCA ground shells
I would like to, what would be your recommended cleaning solution for that?

You have not mentioned which type of "Deoxit" you have.
Good point. I have DeoxIT D5, DeoxIT GN5, and CRC QD Electronic cleaner. (Purchased after watching a BlueGlow Electronics YouTube repair video)
 
I would like to, what would be your recommended cleaning solution for that?


Good point. I have DeoxIT D5, DeoxIT GN5, and CRC QD Electronic cleaner. (Purchased after watching a BlueGlow Electronics YouTube repair video)
Deoxit!!!
Clean with D
Protect with G

By the way, I oriented the Yamaha receiver on it's side (selector switch oriented up and down) so that the Deoxit D would have the best chance of creeping along the full length of contacts. Work the selector switch back and forth through all the input settings. Same thing with G after cleaning.
Still not a permanent fix but it helped.
 
Put the WD40 in the garage where it belongs! Never, ever put it anywhere near electronic switchgear, especially anything with plastic or nylon in it like the switch concerned.

De-oxit is a temporary fix and I never use it. But unless you are skilled with removal, careful dismantling and complete cleaning of the selector switch, you can easily access the twin contact rails and squirt in your De-oxit, as the switch is an open frame design.

Here's what you would typically be dealing with inside a typical oxidised (this is a toggle selector, but the contact principle is the same) switch. The copper contacts are silver plated and oxidise, getting dirty from the festering lubricant etc. The contacts and rails must be cleaned. The contacts are small, easily deformed and must be carefully aligned in the mouldings when reassembling.

 
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But unless you are skilled with removal, careful dismantling and complete cleaning of the selector switch, you can easily access the twin contact rails nad squirt in your De-oxit, as the switch is an open frame design.
Thank you for the advice, and the link to the post showing before and after.

I'll start with the temporary DeoxIT approach, see how long it lasts, and then consider if I am feeling up to risking it trying the disassembly cleaning approach.
 
Thank you for the advice, and the link to the post showing before and after.

I'll start with the temporary DeoxIT approach, see how long it lasts, and then consider if I am feeling up to risking it trying the disassembly cleaning approach.

I think that's the best approach for you.

Switch removal, dismantling, cleaning, reassembly and replacement on the PCB is a specialist job and the preamp is a classic. You don't want to wreck it or be searching for one of those Alps switches.

Things to watch out for are the Hitachi epoxy potted reed relay (the green thing with six legs), which is likely the output muting, they can fail and your output will disappear. Basically, the compound (epoxy stuff) eats into the enamelled copper wire coiled around the twin glass reed switches, but if it hasn't happened yet, nearly 45 years on, you'll probably be OK.

I have an Akai UC-A5 here, which is the same construction (inverted die-cast casework) as your Technics and made around the same time. The Japanese were obsessed with high quality mini sized HiFi at the time and most brands had some seriously cool products in small form factors.

Also, look for a loose grub screw rattling around in the case:

1708896901886.png
 
Here are the specs for your Technics SU-C01:

1708898679249.png


And in the 1982 stack (note it was pre Compact Disc so there was no dedicated 'CD' input yet)

1708898886929.png


In 1982, pulse power supplies (SMPS) were all the rage and pretty much all brands were packing them into their 'mini' HiFi, especially in Japan. Sony, Aiwa, Technics, Akai all made gorgeous systems, often with single piece cast alloy casework to be more 'premium'.
 
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Here's a few shots of the internals of an Akai UC-A5 made in the same year (1982).

Notice the basic contruction similarities. These components were only 1ft wide! (280-300mm)

Die cast single piece casework.
Assembled 'upside down' so no visible screws and a solid appearance.
Same Hitachi gold contact, hermetically glass enclosed reed relays x7.
High quality gold flashed terminals.
Very high quality MM and MC stage built in

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