Fixing a DTK PTM-1230C \ VOGONS

Fixing a DTK PTM-1230C

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First post, by Deksor

Posted on 2020-05-16, 16:10

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Hi !
From a lot I bought back in october 2019, I have this terrible looking 286 board.
It's a DTK PTM-1230C

This board came with a squashed AT connector, bent pins, etc, and some battery damage but I already treated those.

Now it's also needing a good cleaning (no shit sherlock 🤣) and worse, it's missing several components :

Two quartz

And many capacitors

Now I believe the board can at least do something without several capacitors, but it can't work without these quartz !
Which quartz used to be there ?
The 14MHz quartz is still there, one had to be 33MHz (the CPU is a 12MHz 286) and what could be the third quartz ? 32.768KHz quartz ?

Any help would be appreciated 😀

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Reply 1 of 8, by derSammler

Posted on 2020-05-16, 16:16

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The 14 MHz one is always there.

If the CPU is 12 MHz, the main crystal should be 25 MHz (12.5 MHz is the resulting speed for these CPUs). The third one is not needed and only for the FPU. It's optional.

Last edited by derSammler on 2020-05-16, 16:18. Edited 1 time in total.

Reply 2 of 8, by Deksor

Posted on 2020-05-16, 16:17

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My bad it's missing three Quartz and not just two.
According to here, OSC2 is a 1.8432MHz quartz https://91.img.avito.st/1280x960/5330760291.jpg
(and also 2x 12MHz != 33 Duh)

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Reply 3 of 8, by Horun

Posted on 2020-05-16, 16:38

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Deksor wrote on 2020-05-16, 16:17:

My bad it's missing three Quartz and not just two.
According to here, OSC2 is a 1.8432MHz quartz https://91.img.avito.st/1280x960/5330760291.jpg
(and also 2x 12MHz != 33 Duh)

Odd, never seen that before. Wiki says it is typically used for UART, so maybe is used for the Serial/Parallel ports ?

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 4 of 8, by Deksor

Posted on 2020-05-16, 17:04

Deksor Offline

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So I've found a 24MHz quartz but still no sign of life yet.

However now the reset line gets low (before that it sayed constantly on)

On the other hand I noticed that things are even worse than I thought, look what I've found :

Whoever touched this mobo should stay away from a soldering iron forever 🤣
I've even found tin inside some ISA slots !!
I guess I'll have to populate more quartz, clean the mobo and maybe check the BIOS to make sure it's still ok since one sticker went off.

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Reply 5 of 8, by quicknick

Posted on 2020-05-16, 19:59

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Y2 is the 32.768KHz for the RTC
1.8432MHz is for the 82C452 UART, I think the board should boot without it but I'd remove the chip entirely to be on the safe side.

Give the board a good scrub before continuing, those solder blobs can kill a chip instantly.

Edit: also missing is a variable capacitor (VC2 near Y2) and possibly the resistor R69, check on the other side for any signs of this being desoldered.

Reply 6 of 8, by Horun

Posted on 2020-05-16, 20:15

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quicknick wrote on 2020-05-16, 19:59:

Edit: also missing is a variable capacitor (VC2 near Y2) and possibly the resistor R69, check on the other side for any signs of this being desoldered.

Good eye ! That would be to tune the clock for mono/color adjustment if memory serves me proper.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 7 of 8, by quicknick

Posted on 2020-05-16, 22:05

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Being near the 32.768KHz crystal, my guess is that its purpose is fine-tuning the timekeeping.

Also, the KBC seems to be missing.

Reply 8 of 8, by Deksor

Posted on 2020-05-17, 02:24

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I just took the KBC off because of the battery leakage, to take a look.

As for the soldered pins, unfortunately I powered the board before I saw that ...
Hopefully it didn't damage anything !

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

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