Circuit board help needed

[AnthonyL]

My c1973 Sony TC-252 Reel to reel tape recorder has long had an intermittent problem with the left channel which will become distorted and broken up on play back. There are two large buttons on the front panel which work through an interlocking mechanism and ultimately pushes/pulls two rods (one for each channel). Jiggling these buttons particularly the left one fixes the problem for quite a while that session, though if left on for an hour or two the problem recurs and will not go away until everything settles again.

Both rods move freely. I can't get to see where the switches are without massive surgery to get to the other side of the board.

I know next to nothing about electronics. I have a soldering iron and can check for continuity with a multi-meter.

A view of the circuit board is

I don't know what the greenish stuff is and the board is as from manufacturer so any botching was done by Sony.

Any way I can get to the bottom of this problem?

Many thanks.

[jrwalliker]

The problem may be that the switch contacts are corroded and in that case spraying a contact cleaner into the mechanism might help.

Some of the solder joints in your photograph look dubious. In particular, there seems to be poor wetting of some of the switch pins. If you feel confident enough you could remove the old solder using a flux-impregnated desoldering wick and then resolder with flux-cored tin/lead solder, ensuring that the switch pins are well heated and rubbed by the soldering iron bit to remove metal oxides from the surface. Having plenty of flux makes a big difference, but try to avoid getting it into the switches.

John

[Andrew Mawson]

A quick squirt of switch contact cleaner should sort it out:

|pcrid|78108291309|&gclid=CJWunrqoz8wCFUyeGwodIzwEcw&CAWELAID=120173390000014234&CAAGID=14983536189&CATCI=pla-131288067669&CAGPSPN=pla

Andrew

[Dave Liquorice]

Cleaning and lubricating the contacts properly would probably work. Squirts of "switch cleaner" is generally only a quick and short fix. The cleaner washes out an lubricant and in dirt that then grinds away the now dry contacts on each operation...

Just heating and adding a bit more flux cored 60/40 leaded solder will probably do it. If excess solder did need removal I find a desolder pump far easier to use than braid.

The green I think is just ink there are similar blue and black markings in other places.

[AnthonyL]

Though as I said I can't readily get to or even see the electric switches - can I just spray around??

[AnthonyL]

As per my reply to Andrew I can't actually see where the switches are but also the problem started only a couple or so years after I purchased the unit so corrosion isn't high on my thoughts.

I was quite taken aback when I saw the quality of the work which makes some of my soldering look good.

Sounds like a lot of work - is it really necessary to remove the old stuff? Can't just re-heat and let it re-flow?

[newshound]

IMHO, no. You need to find the switches and spray it into the interior. Another possibility, if the switches are soldered directly to the board, is that you have dry joints and/or broken tracks between the switches and the circuits. This is the location where mechanical stress coincides with solder joints, generally a bad combination.

(Which reminds me of dismantling odd "army" hardware such as field telephone boxes, bought from street markets around 1960. The War Department spec, apparently, was that every wire had to be wound at least three times around each terminal).

[cl]

Well soldered joints should be mechanically sound without solder, that was certainly a requirement back in the days (1960s) when I spent a little while inspecting joints.

[tabbypurr]

Typical of early 1970s construction. Hand assembled in what was a country i n financial trouble around that time.

The rods that get pushed run inside long switches mounted on the pcb. Such switch contacts usually come through the pcb in 2 rows. As said, switch con tact surface corrosion is the usual culprit, and is pretty much universal i n machines of that age. Bad soldered connections to the PCB also sometimes happen. Sometimes you can remove contact corrosion by waggling the switch b ack & forth many times.

Re resoldering switch pins, any soldering work needs to be immaculately cle an or it usually won't stick. If the soldering was bad there will be crap o n the affected switch pin, which must be completely cleaned off to get it t o solder properly. Be aware that such kit usually used paper/phenolic pcb, which is far from tough & durable. Desoldering can easily remove a track.

So operate the switch back & forth lots of times. If that doesn't do it, ta ke it to someone that can resolder it without wrecking the pcb.

NT

[Geo]

As others have said, switch cleaner on the contacts would not come amiss. You need to get to the top side of the board for that. The switches seem to run virtually the whole length of the board down the middle.

Looks to me like it has either been "repaired" before or the factory had a LOT of trouble - the eight different coloured wires at the top of your picture just seem to be in parallel with the copper tracking - maybe someone had track/joint problems - but seems odd that a service tech would use so many colours and do the job so poorly. Likewise the brown hairpin wire just right of centre - the joints even have blue marker so unlikely post-production.

The left channel would appear to be the right-hand board in your picture. Pay attention to a couple of joints near the top which look very suspect. I think they might be screw heads of a pair of 2SD28 TO3 power transistors. The schematic is available here:-

[Brian Gaff]

Well sadly Sony slide switches were known for this sort of problem Some kind of 'gunge' was put into the holes where the pins that end in the contacts are held and this breaks down over time and then only the soldered connections in the pcb hold them. The lack of pressure when the contacts slide makes them not make very good contact. In my case this was a luggable cassette machine which ended up quite early in life needing completely new slid switches fitting, but after all this time I doubt any stocks exist. the last time this machine went intermittent many other switches seemed to have the same creeping gunge issue so I reluctantly had to send it to the great studio in the sky.

That was a tc158SD. I used to also have the reel to reel tape corder Tc366 was it, cannot recall, its main issue was that the level controls went noisy very quickly. Apparently this was caused by capacitors going leaky allowing dc to go through the sliders. I sold it working quite early on as the heads seemed to be wearing quite fast.

I suppose you might be able to clean the slide switches, but be careful with any solvent based sprays as they used the same gunk in their headphone sockets and ordinary Elecctrolube ruined on of these on a mixer I had which was clearly the same make Sony used with the blue or red gunk. Brian

[AnthonyL]

Ah - so you're saying all those connections are go to switches which run in a column that I can't get into on the other side?

It has to be the latter - I've had it since new (not refurbished) and it has never been in for repair. This is the first time I've been bold/stupid/brave enough to get to the electronics.

The unit has an added complication/feature in that it had a facility called "Sound on Sound" so could record on a track whilst playing back. That might account for additional switches/switch logic.

[AnthonyL]

I'm having problems understand what holes these are. Are they visible in the photo or are they on the other side or within the slide switch?

Is this "gunge" a conductor/lubricator/insulator? What was it's purpose?

Thanks

[AnthonyL]

It's seems that these are problematic Sony slide switches. So maybe nothing to lose squirting some cleaner up the inside of the channel in which they are enclosed.

Yes I've got one of them - slurp.

Makes sense. Someone had suggested the green may be copper leaching through but that doesn't account for the other colours.

[Dave W]

If you can get to the other side of the board, you might be able to slide the whole moving bit of the switch out for cleaning. Be warned that the moving contacts may fall off and make replacement problematic.

[tabbypurr]

The ink marks are engineer's blue & other equivalents thereof. A different colour mark was used when a unit had passed a certain test or a certain level of assembly was completed. Standard early 70s practice.

NT

[AnthonyL]

Thanks for that nugget of information.