Telefunken TC 750 - A new challenge!

[laatsch55]

That's what I would call a complete teardown...excellent!!

 

[vince666]

thanks, but i will need to repeat part of the work and add more work to restore it for good.

the hint by Leo about a missing ground at the output was right!

at now, with the RCA output attached to my amp for listening, i added also the second cable from the amp to the RCA inputs, then providing the ground also to the output.
this way, both channels finally arrived and in phase, then this is definitely a matter of ground.

anyways, the sound is a bit weak and quite distorted/unclean, both in source mode and in play mode, then at least all the electrolytic capacitors need to GO!

 

[J!m]

Looking good!

I noticed an adjacent bad solder joint next to the one you repaired- id check them all with a 10x loupe and reflow any in question.

And I would have wasted at least one can of electrical cleaner on the transport before I started tearing it down! That thing was nasty!

 

[Bob Boyer]

That's an amazing restoration job, Vince. Can't wait to see it completed. Appreciate you taking us along on the journey; I have once again confirmed that Nakdoc has been a very good friend to me over the years.

 

[vince666]

I noticed an adjacent bad solder joint next to the one you repaired- id check them all with a 10x loupe and reflow any in question.

J!m, you mean another cracked joint here in this same picture, near that one i've just repaired? (not yet repaired on the picture, though)

 

[J!m]

Yes; I don’t like the look of the one just to the left of the “R” and also due north of the obvious one.

Seriously- if you have the boards out anyway, check each connection with a 10x loupe and reflow any suspect ones (after a washing and scrubbing with electrical cleaner and toothbrush). I’m more mechanical than electrical but bad mechanical joints are no good for electrical…

 

[vince666]

that one is a PCB which is quite easy to pull out of the deck.
will reflow those joints.

that said, when i will need to unmount all the PCBs again for full recapping, will also reflow all the solder joints.

 

[nakdoc]

I like the switch work.I thought I was the only nut who took switches apart.

 

[J!m]

ESL takes switches apart. They don’t believe in deoxit.

Part of the reason they are so expensive…

 

[vince666]

first time i had tried to take switches apart, it was immediately clear because this is the way to go.
deoxit sprayed on a closed dirty switch simply helps moving the crap around a bit.

 

[mr_rye89]

Maybe I should start taking apart switches. The radio in my office (which I “restored”)sometimes plays AM and FM at the same time lol

 

[J!m]

I think deoxit, like any other tool or chemical, needs to be used properly. Soaking a switch with D50 will help, but yes, it will redeposit somewhere else.

I use D100, but only after I’ve cleaned the contacts with contact cleaner. Wash the crap out first, and then treat the contacts with the deoxit.

But full disassembly is great if reasonable to do so. Some non conductive (silicone) grease can help but it has to go into a clean assembly too…

 

[vince666]

when I started disassembling switches for the first time, like very few years ago, I never looked back.
yes, it's a lot more work but wow.... they return just like new.
and especially on the older decks, many of them are just into the signal path.

 

[George S.]

I need to start doing the same. I assume, disassemble, clean with a Q -tip and alcohol, grease with Deoxit grease, reassemble. Do you do anything special with the contacts? Kind of concerned about alcohol on plastic or graphite/carbon resistance strips or rings. From your experience, what's best practice?

 

[vince666]

I noticed that, to clean those very dirty contacts, the rubber eraser (like the one you can see there in a couple pics) is the fastest and easiest way to clean them.
but, yes, i use alcohol quite extensively while cleaning.

 

[20tajk7]

Alcohol doesn't harm plastic, sometimes it can remove ink marks.
I also use a fiber glass pen for hard to remove traces.

 

[George S.]

I've been injecting pots and switches with Deoxit using a syringe, then injecting grease, but results are mixed. Thanks for the info, going to start taking them apart and doing it right. Thanks.

 

[vince666]

about pots, not all of them can be opened (or, at least, i wasn't able to) then i must use the spray method.

 

[J!m]

Pots that don’t open without distruction I flood with cleaner, let set/soak, and then repeat as often as needed until the trailings are clear.

After it thoroughly dries, I give’er a spritz of D100.

This won’t help a dead spot but otherwise works very well to stop the scratching.

 

[borchee]

Ciao Enzo,

you have done an admirable job!!!...but...the Giovedi-push-button-switches...
You cleaned the contact-sliders, yet not the pins/legs! The housing can, I presume (Revox B750 Schadow switches), be taken apart to give you acces to the "legs".

Regarding the rubber-eraser...are you fond/in possession of a mechanical/analog typewriter?

Borut