DTK Tech-1230C (Apex 286/12, PTM-1230C) Error 8742 Controller POST error

[KLund1]

I got a nice condition DTK Tech-1230C turbo 6/12mz 286 machine. On boot I get error 8742. The manual at MinusZero shows that is a generic controller error code. There are no cards in it except for the working color video card. That manual is for a bit newer MB. Mine has rows or ram chips not simms. I did look closer at the board and it shows it as a PTM-1230C. And I found this manual
https://stason.org/TULARC/pc/motherboards/D/DTK-COMPUTER-INC-286-PTM-1230C.html
And it is what I have. From that I disabled the LPT and Com ports( pulled jumpers J13,15,17) but still get the same error. The mem jumpers are set right for 1mg. I reseated all the large socketed IC's. I pushed down all the ram chips.
Any suggestions from those smarter than I?
Thanks

 

[modem7]

Any suggestions from those smarter than I?

More knowledgeable, not more smarter.

On boot I get error 8742. The manual at MinusZero shows that is a generic controller error code.

"8742 Error - Indicates a 8742 controller error"

The 8742 controller is a large chip on the motherboard. (8742 = EPROM version / 8042 = ROM version)

Some IBM AT examples are pictured at [here].

Typically used in AT-class systems as a 'keyboard controller', although it is typically used for some other functionality as well. IBM AT diagram at [here].

It sounds like the motherboard's power-on self test tried to communicate with the 8042/8742 controller chip, and when that failed, displayed the 8742 error.

First, do a very good visual inspection of the 8042/8742 controller chip, concentrating on the pins and solder joints. Note that the problem cause may not be the 8042/8742 itself, but one of the chips that supports it.

 

[modem7]

By the way, I can supply a replacement 8742 keyboard controller, as I have already done for some VCF members here.
There are risks:

- Per my earlier post, it might not be the 8742 keyboard controller that has failed.

- Motherboard damage if desoldering/soldering not done properly.

- What I supply is an 8742 that has been programmed with the same code that is found in the 8042/8742 of the IBM AT (IBM 5170) and IBM XT/286 (IBM 5162). They also work for the majority of the clones of those machines, but there are some clones where the programming code in the 8042/8742 contains extra functionality. If your computer is of the latter, then what I supply will not be suitable.

 

[KLund1]

Hi, Im back to this after the holidays!

I got a new 8042 IC, looks exactly the same. And it looked like a new IC.
Sadly there what no change on power up. I get the same error as in post 1. There was a Varta battery next to this IC on teh MB. It was just starting to leak. I removed it and cleaned the MB surface. There dose not appear to be any acid damage on either side of the board. But that dose not mean there is not something wrong in one of the internal layers of the board. The is some blue corrosion near R73, nut I do not think any acid actually got there. There are a couple traces that appear to terminate under the battery. Those trances are a bit corroded.
I was thinking I might reflow any solder point near the battery. Would this be helpful, or a waste of time? Other suggestions?

 

[modem7]

I got a new 8042 IC, looks exactly the same. And it looked like a new IC.

So, you are very confident that the replacement 8042:
1. Is programmed to provide keyboard controller functionality (not instead programmed for something else, like a microwave oven); and
2. Is not faulty.

 

[KLund1]

Absolutely no way to tell from my knowledge.
In the pic the top IC is the new one.