Siemens TGN2 (Receive Only T1000)

[M1ECY]

This evening a museum dropped this machine off with me for test/repair.

This is a British machine, and as far as can be seen operates using something close to RS232

Any suggestions regarding generating a signal source for testing would be appreciated

[M1ECY]

Update

Wow, was it really May 2021!

Anyway, yesterday I finally got the machine on the bench, physical condition maybe 7/10 a lot of surface corrosion on the chassis, and some of the plating on the controls panel is corroded.

I had made a bulk purchase of 10uf 50V capacitors recently, so I was armed and ready for battle. The cost of Tantalum capacitors is sufficiently high now that I decided to use standard 105C Aluminium Electrolytics, reasoning that more modern components would be of at least a similar quality as the original 40+ year old components.

I didn't even bother to power the machine up - immediately replacing all of the 10UF capacitors on the main board, the LAT and the STT board. I also replaced the 4.7uf capacitors on the print driver board (using the same 10uf capacitors)

This all took a couple of hours, and the boards look reasonably neat even though the true components have not been used.

I decided to power the machine up.

POP!

Oh dear, a rather loud death like noise came from the power supply, interestingly, no smoke.....

Quick post mortem on the PSU found the main bridge rectifier doing anything but rectifying, so having a suitable replacement in stock, this was fitted.

Decided to meter out the main reservoir capacitors (Called "Ears" as Henning said) - resistance readings looked to be about right, so I tried running them up on a bench power supply, this told me a very different story - Capacitor 1 (on the RED wire) reformed quite well at 250VDC showing a leakage current of 1.7ma.

Capacitor 2......

45V applied - Bench Supply tripped.

Okay, try again..

35V applied - hmm, 560ma leakage current.....

Okay, so that is past it's use by date.... Much grumbling and groaning - these monsters are probably unobtainable, or expensive, or possibly both...

Stopped work on PSU.

Fitted spare PSU from other machine in workshop (known to be working) Hmm, now not working..... Ah, fuse in rear panel of machine.... replaced... Aha! Machine powers up.

Time to connect the telegraph tester.

Now, being British, we do not like using handy European colour schemes for cables, and being Military, we wouldn't use an easy to find connector either....

So, the Socket needed to mate with the original connector is : Cannon C2092 12 10 FNO

Connections as follows

Pin B RXD-
Pin J RXD+

Pin D TXD-
Pin C TXD+

.
With the test set connected, oh, and the cover switch defeated (Thanks for the tip Sebastian) the machine burst into life.


Once I have cleaned the case up and had a bit of a tidy of the warzone that is my workshop, I will post a couple of pictures, and some video.

The machine works at all speeds, 50, 75 and 100 Baud


Parts for the PSU arrive tomorrow, lets hope that is a simple fix..... More to follow.

[M1ECY]

Update

Power supply put up a fight - seems that the rapid death of the rectifier also managed to see off the useful life of the BC337 that controls the soft start relay....

Power supply now all working as it should and machine works flawlessly.

Used these capacitor from Farnell UK to replace the 500uf 250V Siemens capacitors that hide in the "Ears"

ALS30A471DE350

These are 470uf @ 350VDC - The PSU is switchable between 110 and 220v internally - either voltage doubling from 110v, or running as a bridge in 220v - whilst the original capacitor voltage would have been adequate, having a bit more headroom helped with the mechanical constraints - these cans being almost exactly the same size as the originals.

So far so good - hopefully get the machine back to the museum it belongs to shortly..... Next on the bench.... another T1000.....