Chips F82C235 NEAT chipset from early 1990s common issue?

[eduardogomez]

Anybody on here has any experience with early 90s 286 PCs with Daughterboard equipped or controlled by Chips brand F82C235 Neat chipset?
I got two of these boards and neither is booting past memory check prompt, after swapping around every single component I still have the same issue
the only chip I can't swap out is this chip because it is soldered to the board. My question is if this controller have common failure rate?

Here is the link on what I am trying to fix: https://www.eevblog.com/forum/repair/snap-on-mt3505-emission-test-computer-repair-help/

[amyk]

Don't know about that chipset in particular but a datasheet seems easy to find, so if you have a scope or LA I'd recommend checking the signals on the RAM to see if they look right.

[bobxyz]

Try rummaging around here: https://bitsavers.org/components/chipsAndTech/
 there are various datasheets and an example NEAT schematic too.

Can you get into the BIOS menu, or does it fail before that?

[eduardogomez]

Can you get into the BIOS menu, or does it fail before that?

I got the schematic and during testing the chip gets everything it needs. I am unable to get into bios because this is not a PC but a testing machine. It is self booting. But it doesn't boot, it is stuck on prompt

if you have a scope or LA I'd recommend checking the signals on the RAM to see if they look right

RAM gets checked upon boot and then anything further stops. Problem is that I don't have the repair manual for this machine.

[squadchannel]

Could you please record a video of the boot process?

It gets stuck at the RAM test prompt?
If that's the case, suspect the DRAM.

It looks like you’ve removed the battery . Have you tried putting it back in?
Some boards won’t work unless the battery is installed.

Even if get the service manual for this machine, it probably wouldn’t contain much useful information.

[amyk]

When it "stops", what is the CPU doing? Is it actually in shutdown (on a PC-compatible, this causes a reset), running in an infinite loop, or busy doing something else like waiting for a peripheral that never comes out of reset? This is what an LA should be able to tell you if you put one on the signals of the CPU.

[eduardogomez]

running in an infinite loop, or busy doing something else like waiting for a peripheral that never comes out of reset? This is what an LA should be able to tell you if you put one on the signals of the CPU.

I got two boards, one checks the time and tells that the time is not correct then it corrects the time, then it checks the memory, then the memory is checked good then it stops with prompt flashing. Other board boots without showing that the time is wrong, it just checks the memory, says it is all good then goes to check the hard disc then it is stuck on checking hard disc, but there is no hard disc on the board. It is a testing machine, not a PC. The way that this machine works is that it won't boot to main screen if it fails self test and it won't tell you what the problem is.
But my main question is that NEAT chip

[indeterminate]

I cannot remember ever having one fail.
Given your description i think it would be more likely that the battery backed sram contained configuration data that is now corrupt.
Looking for a hard disk that is not there is a big clue.

It could be water ingress into a IC after sitting around in damp conditions for decades but given that the cpu is actually executing instructions i would be looking for the sram configuration data.

[eduardogomez]

I cannot remember ever having one fail.
Given your description i think it would be more likely that the battery backed sram contained configuration data that is now corrupt.
Looking for a hard disk that is not there is a big clue.

I just found out today that there is a socket to plug in old PC keyboard on the board. Then I looked at the Bin file of the main chip and it does mention Bios when I look at it with hex reader. Maybe I need to try that, when it is stuck on "prompt" to ctl+alt+s or whatever boots 286 pc with NEAT chipset. Like you wrote, most likely bios needs to be configured out again after bios battery went dead. I did wire up the keyboard to it and don't know what keys to press to get into Bios if that is even possible here. I think this machine has self setting bios configuration.