Fixing an Intertan DT-88 (Tandy 8088 clone)

[Deksor]

Hi, so I just got this Intertan DT-88 computer to play with.





The computer turns on, but its hard drive, a Seagate ST325X doesn't spin up anymore (and it's not the platter that are stuck, because I can move the spindle found under the hard drive perfectly fine)
. It seems like it's a board's failure (or a motor failure maybe) rather than a mechanical one, but I don't know what could have failed there.

Also, its floppy drive can't read anything and "crashes" after the POST. The seek test works, but I can't boot from it. Fortunately using another drive works, but I'd like to keep that machine as original as possible.

The drive is a 1.44MB 3.5" mitsumi floppy drive
I've attempted to lubricate the rails and the stepper motor's worm, but it didn't help much (although the drive is at least more silent now). I'm thinking that maybe it can't move its heads properly anymore.

Then, there's also the DALLAS battery that died, but I have enough soldering skills to swap it.

However there's a much bigger issue related to this ... The computer asks me to configure it using a program named "SETINIT.EXE". But I can't find this anywhere ... There's little information about this computer online (not even a picture of it), and it seems some people have asked about this back in the early 2000's, but I couldn't find any good answer ...

Can anyone help me ?

 

[Deksor]

Here's the HDD's PCB by the way




I checked the voltages on the platter mottor cable and the highest one I saw was 0.2V so I doubt it can start with such a low voltage.
Also, there are some components that look like resistors with a "0" written on them. Are these 0 ohm resistors ? Because none of them have a 0 ohm resistor.

 

[Chuck(G)]

SMT resistors with 0 on them are just that--zero-ohm jumpers.

I suspect one of the generic CMOS setup programs might work with your system.

What are the PSU voltage outputs? Do you have a solid +12V?

Most signals on the floppy and XTA buses are active low, so don't read too much into the signal level voltages.

 

[Deksor]

Thanks, so I replaced the 0 ohm resistors with bridges I made myself, because they are seemingly dead.

I tried GSETUP on the computer, but it didn't work well and crashed all the time.

The PSU outputs 11.1V for 12V and 4.6V for 5V. That's a bit low, but the computer works with these voltages nonetheless. Even by using a different PSU, the problems are exactly the same.

As for the voltages, I just measured the pins leading the the HDD's platter motor, not the signals in the IDE cable. This and the bad 0 ohm resistors suggests that this drive's controller card is bad. Unfortunately I don't know what to do now. Should I replace the caps ?

 

[Deksor]

Time to remove the RTC which was soldered !



New socket in

The pins on the grounding were quite tough to empty, but in the end I managed to get rid of all the solder.


Now the RTC is in a socket


Also I opened the PSU to check that everything is allright


The caps are made by Samsung for the most part. I don't know if they're still good, since the voltages seemed a bit low, I may change them at some point

Speaking of caps, here's a closer look at the HDD's caps.


And also I measured some odd voltages on these two transitors nearby the molex connector :


On them I can read "CEC P09". I don't have much knowledge in electronics, but that looks suspicious doesn't it ? What are they supposed to do ?

By the way, this computer is a really late 8088 machine ! Just look at the case's manufacture date !

 

[T-R-A]

On them I can read "CEC P09". I don't have much knowledge in electronics, but that looks suspicious doesn't it ? What are they supposed to do ?

Nothing suspicious about it. The CEC is the marking for a small signal transistor (PDF File):

https://www.taitroncomponents.com/catalog/Datasheet/BC869.pdf

The P09 is likely a (in-house) date-code.

How are you measuring the voltage on them? It's possible they're bad, but something else may be dragging them low.

 

[Deksor]

I just use my multimeter. The - probe is put in the GND pin of a molex of the PSU, and I use the + probe to measure on the component's legs what voltage is.

So far I haven't been able to find any shorts in that board.

 

[T-R-A]

So far I haven't been able to find any shorts in that board.

Components don't have to be complete (0 ohm) shorts to drag down voltages. Anything that doesn't appear right (>100 ohms when it obviously should be higher) would be suspect. Would be good if you could find another (good) board to verify against, but then you wouldn't have to worry about your current one if you did. The fact that you stated that your 0-ohm resistors were "seemingly dead" (which I assume meant "open") leads me to believe that there's something else seriously wrong on (or leading into) that board.

 

[Deksor]

I don't remember seeing anything like this.

Indeed you are right, this board is quite suspicious. I fear that the custom chips may have died as well ... But I wonder what could have happened there to kill that many components if the rest of the computer is fine ?

Yes the 0 ohm resistors were open. Except one which had a 100ohm resistance.
I may end up buying a working board, but I can only find one ad selling these ST 325X and they're rather expensive (they're in NOS condition so it's fair, but I don't need a NOS drive for that :/ )