Circuit board for vintage 400 day clock

[mu2]

Hi,

I'm trying to get information about a circuit board for a vintage 400 day clock.
I am not sure of the brand name of the clock but the marking on the underside of the circuit board say "Hermle" and there is a number "865".
The jeweler who is repairing the clock says it's an electronic problem and removed the circuit board for analysis.

Can anyone identify the component in the top side photo? It might be a transistor but it has four leads. The only marking is a partial number that might be "780". The case is a reddish color and has a sloped area on the case facing downward to the resistor.

I have never seen a part like this and can't find anything on the internet.

Does anyone have a schematic of the board?

A friend contacted a clock repair company who said they contacted "Hermle" and the circuit board is no longer available. Repairing the board is the only way to fix the clock.
I don't see any bad solder joints and have checked continuity on the red and green coils. Hate to unsolder any parts specifically around the coils as the coil wire is very fine.
Any help would be appreciated.


Thanks,
Mike

[stj]

Re: Circuit board for vintage 400 day clock

transistor, resistor, 2 capacitors - probably.
you need much better pictures though.

[redwire]

Re: Circuit board for vintage 400 day clock

Appears to be for a Hermle 865 clock. People still sell springs for it.

Look at the Bulova Accutron schematics, it is a PNP transistor. Only three unique terminals? The fouth pin goes nowhere?
Better pics to sketch a schematic would make it easier. I've only seen RF transistors in that pill package.

The green capacitor? probably needs replacing, and the black part is a puzzle. The resistor is likely out of spec. I'd replace all the components, it's not much.

Zetex make transistors with very low saturation voltage and high gain like ZTX1147A.

https://electronics.stackexchange.co...spaceview-work
http://jestineyong.com/bulova-accutron-214-part-3/ special test jigs

[R_J]

Re: Circuit board for vintage 400 day clock

It may be a similar circuit to this one. Seems to be a SOT-103 case style

[mu2]

Re: Circuit board for vintage 400 day clock

Thanks for the responses.
The green item is a 15mf 3v tantalum cap. The black item is a ceramic cap .056 3v and the resistor is 100k. The resistor checks ok in circuit. Haven't pulled the caps yet but they aren't shorted.
I'll check into the case package for the transistor.
Mike

[R_J]

Re: Circuit board for vintage 400 day clock

This site has a similar clock, transistor is green https://uhrforum.de/threads/hermle-t...rk-955.112675/
The transistor seems to be a TAA780. It seems to be a module

http://www.colysa.ch/shop/index.php?...&search=taa780

[redwire]

Re: Circuit board for vintage 400 day clock

My guess it's European Telefunken and the pill package TO-50 or SOT-37 I am used to seeing in RF transistors but in black epoxy. Not red or green. Very rare.
The only question is if the transistor is Ge or Si. Can you get a junction Vf reading on it? The coils might get in the way.

edit: It's an IC, not a single transistor

[mu2]

Re: Circuit board for vintage 400 day clock

Wow! That is an exact match for the transistor - except for the color of the case.
Mike

[stj]

Re: Circuit board for vintage 400 day clock

you probably need an esr meter to be sure of the caps.

[mu2]

Re: Circuit board for vintage 400 day clock

More info on the mystery part. This German website shows the contents inside the package. That's why it has four leads.
Also a sort of application circuit.
http://www.hwynen.de/taa780.html

Mike

[redwire]

Re: Circuit board for vintage 400 day clock

Wow, good detective work to the early 1970's. I was wondering as the movement has two pair of magnets and that needs more than one transistor I think. The later part TDA840 is like a half-bridge and only needs one coil.

TAA780 IC made by ITT - Intermetall Semiconductor. Also used in Hettich caliber W41. I can't find that URL on the guy's website now, it's not indexed at all.
I would suspect the tantalum cap even if it tests OK, it's pretty old.

[mu2]

Re: Circuit board for vintage 400 day clock

I'd like to thank Redwire and R_J for all their help in resolving this issue.
The clock isn't fixed yet but I'm light years ahead of where I was before posting the message.
Identifying the ic was very important.
Thanks again!

Mike

[R_J]

Re: Circuit board for vintage 400 day clock

Let us know if you get it working, I guess time will tell.

[mu2]

Re: Circuit board for vintage 400 day clock

Hi,

I'm finally able to close this thread and I'm happy to report that the clock is working!
My friend contacted this Ebay member from Great Britain that listed a TAA780A.
https://www.ebay.com/itm/TAA780A-Sem...3897:rk:1:pf:0

There was no photo of the part in the listing and after a while they provided a picture. The part appeared to be the same except for a different color case. The part was ordered and installed in the board. We also replaced the tantalum capacitor - just for good measure. The original checked ok for value. The TAA780A works as a sub for the TAA780.

If anyone attempts this repair the only critical thing is that the TAA780A needs to be installed as close to the pc board as possible. There is a mechanical adjustment part directly above it and if it is not flush it won't clear.

Thanks again to all that helped. There is no way it would be working again without help from this forum.

Mike