exxos's Atari, Amiga & retro forum

Hi @all,

this is my first posting - so let me introduce myself briefly:
My name is Rüdiger (living in germany) and my first Atari was a 260ST back in 1987 (which I still have today).

The last entry to my collection was a TT030 presumably in "working condition", but it seems to be dead as a door-stopper.

TT030 specs:
- "daughterboard"-variant
- 32MHz (not 16)
- mainboard is CA400310
- daughterboard is CA400771

Actions taken so far:
- disassembled and cleaned the mainboard
- pulled all socketed chips, cleaned contacts of chips and sockets
- checked a lot of traces with a multimeter
- swapped PSU with a known-working-good PSU (voltages are OK)
- I made myself a diagnostic cartridge and verified it by testing the diagcart with a working TT030 and a RS232-connection to a terminal program
- the fuse at the cartridge port seems not to be blown

Issues found:
- some bent pins of the FPU
- resoldered some suspicious solder joints

No signs of life via RS232 (besides some odd characters sent while turning on/off the TT030)
CPU/FPU are getting warm over time but none of the chips of the mainboard are too hot to touch.
All RAM-Chips are cold to the touch.

Any suggestions for me?

Unfortunately I have no oscilloscope nor logic probe.

My guess is faulty RAM but I have no spares: onboard ST-RAM is Micron MT 4c4256-8 (MT's seem to fail quite often)

Thanks in advance

It might be useful to post pictures of the motherboard especially some zoomed in views around the areas you mention as having issues.

Test the reset button? I've had a few STs that seemed dead but the reset button was "stuck"

DIP-Switches (bottomside)
It seems that some liquid/water was dripping through the block of DIP-Switches at some point.


Keyboard-Connector


More corrosion at the reset-switch and Cinch-connectors (audio)


Near TTVIDEO / PSU-Connector


Mainboard / overview


Serialports

I cleaned the solderside of the mainboard with IPA and reworked some solderjoints.

alexh wrote: 15 Mar 2023 10:00 Test the reset button? I've had a few STs that seemed dead but the reset button was "stuck"

Yes - I checked the reset button: not stuck

Since you are getting nothing from the known-good diag cart setup, you should probably start working through the TT030 Service Manual, starting with section 3.2, "Troubleshooting a Dead Unit".

Some of the testing there unfortunately requires an oscilloscope, but some of it you can do without one. At the places where it says to use a scope to check frequencies, you can use a multimeter to get some idea, as it will average out what it sees, and you'll see some fraction of 5 V. It's not the best tool for the job obviously, but it's better than nothing, and it will certainly reveal if you've got no clock at all.

J100 is connected to the 32MHz oscillator quartz.

I measured J100 of the daughterboard:
DB popped out: 580 Ohms (J100)
DB in place: both pins of J100 are dead short to ground.

R1 (above J100) seems to have an open loop.

But: I have no clue what to do next.

ehm - is it possible that the jumper connector is turned wrong (flipped)??

I turned the jumper /w brown/black cable (black cable is now facing to the socket) and J100 is no longer shorted to ground on both pins:
One pin to ground and the other pin shows 580 Ohms.

Is it safe (in terms of "blowing all up") to turn the TT on or is it even worse?

Yeah!

Silly me ... easiest bugfix ever ...

It freaking works!

A few resets were necessary ( I got a lot of wierd characters on screen), but now its working!
RAM-test: passed ...

Thanks for pushing me in the right direction!

:bravo: