TC01 repair

[Patrick]

Hello,
My name is Patrick and I live in France at Clermont-Ferrand. My first computer was an Amstrad CPC 464. I am an IT engineer and as a hobby I collect family computers from the 80's.

Recently I bought a Tatung Einstein TC01 on eBay.
Sadly, it doesn't work.

The symptoms are:

• Black screen, but TV set detects a video signal from UHV (I don't have a YUV/RGB cable).
• PSU works well, +5V and +12V are OK at floppy power connector (so didn't check -12V).
• Power and ALPHA LOCK LEDs on. If i press ALPHA LOCK key, the LED doesn't toggle.

It was a first quick report. I will have more time on next vacation, this Friday.

I have all the documentation, no disk. I will add a Gotek, with FlashFloppy ASAP.

[chrisv]

Bonjour from a fellow TC-01 'refurbisher'.

Hopefully your further testing will reveal how much work you will have to do (not too much I hope).

[vanpeebles]

Welcome! Fingers crossed

[Patrick]

Thank you for your messages.
Can someone tell me what is the correct behavior of the Einstein right after turning on without disk.

• Does ALPHA LOCK key toggle the corresponding LED?
• Does CTRL-G produce sound?

I suspect that the computer doesn't boot properly (RESET, clock, CPU, ROM...).
I want to be sure before starting hardware investigation.

For the record, as I know that this is collected, my serial number is 6006763.
And I have the duck or chicken or Taiwanese characters (whatever it is) under the top cover

[Patrick]

I started the repair:

• All voltages are OK, 5, 12 and -12V.
• Reset is OK, /RST goes low then high, both at startup and with reset button pudh.
• Clock is OK, 4 MHz on Z80.
• Control signals seems to be OK on Z80 except /INT which goes low quickly after reset and stay in low state.

I am reading the hardware manual. It seems that a lot of ICs can activate /INT. I don't know which of them is prone to fail and to produce this behavior.
As all ICs (but FDC and ROM) are directly soldered on the board, I don't want to desolder all of them, one after ther other.
Any clue or advice?

[Patrick]

More on this.
I checked the RAM and saw that IO12 (D3 bit) was always high. I desoldered it and soldered a socket in place.
I tested without RAM, D3 was moving high and low as the other bits, certainly driven by CPU, ROM or IO devices. /INT was no more active.
I tested with a new RAM. Same problem as before removing the original RAM.

Then I had a look at the schematics from the hardware manual. I saw that there is a 74LS245, IO04, which is a buffer between the CPU and the data bus.
As it was my new suspect, I desoldered it and soldered again a socket.
I tested the 74LS245 with a TL866CS. It seems to be good and I don't have a replacement.

I also tested the desoldered RAM with my own ICT device (you can have a look here . It is in French but screenshots are in English).

I don't know what to do next. May be order a new 74LS245? I am not sure what I can do. There is too much devices driving D3.
But also I don't understand why with the RAM installed D3 is always high. I checked the shared signals with the other RAMs, no problem.

Good point, it is pretty easy to desolder components. I didn't break anything.

[vanpeebles]

Sounds like some progress there, I had to socket all the ram on one of mine.

[vanpeebles]

Hello,
My name is Patrick and I live in France at Clermont-Ferrand. My first computer was an Amstrad CPC 464. I am an IT engineer and as a hobby I collect family computers from the 80's.

Recently I bought a Tatung Einstein TC01 on eBay.
Sadly, it doesn't work.

The symptoms are:

• Black screen, but TV set detects a video signal from UHV (I don't have a YUV/RGB cable).
• PSU works well, +5V and +12V are OK at floppy power connector (so didn't check -12V).
• Power and ALPHA LOCK LEDs on. If i press ALPHA LOCK key, the LED doesn't toggle.

It was a first quick report. I will have more time on next vacation, this Friday.

I have all the documentation, no disk. I will add a Gotek, with FlashFloppy ASAP.

My spare Tatung has just developed this fault! How did you get on?