You don't have to have a soldered-on SX CPU. I don't know about NEC in particular, but it was very common for other boards like that to be sold both ways.

It's possible for a bad cache chip/bad RAM to tie up a system from POSTing like that so you might try removing both. Or, remove and re-seat the BIOS chip if it's removable.

Beyond that, you're in oscilloscope territory unfortunately

jakethompson1 wrote on Yesterday, 02:13:

Beyond that, you're in oscilloscope territory unfortunately

That's what I was afraid of. Super unfortunate...

IMO it's not bad RAM as I have a known good stick from the other NEC Ready 425 that I have and using that RAM changes nothing in this dead system. Also, if there's no RAM in the other functional system, it still gives a beep code for no RAM.

I have an oscilloscope I bought 5-6 years ago but I never learned to use it. I found some basic things to test from an EEVBlog forum post so I guess that's where I am at with it. I've watched enough Adrian's Digital Basement to see him using an oscilloscope to track things down but he often has a diagram and at the very least, he seems to know what he's doing. I have neither of those things on my side so I have low expectations of identifying the problem let alone resolving the issue on my own.

Thanks for confirming.

There are plenty of ways it could be temporarily sabotaged, e.g. if a child played with it, such as by putting a jumper cap over the Reset header. But if you think it's still in the same condition as the last day it was used, it wouldn't be that.

Basically there are ODP overdrives and ODPR overdrives.
An ODP (OverDrive Processor) should require a processor that can be deactivated, an ODPR (OverDrive Processor for Replacement) should behave like a normal processor.
But I do not know how they really behave, and thus on your particular motherboard.

Which type of overdrive processor do you have?

I have heard of the new processor needing to ground the UP# pin (pin C11, defined as NC on the original 80486) in order to disable the soldered-on CPU (https://datasheets.chipdb.org/Intel/x86/486/a … ts/29043606.PDF, p. 32)

I have never heard of an OverDrive processor that needs to be board to also have a soldered-on CPU populated in order to function.

jakethompson1 wrote on Yesterday, 19:27:

There are plenty of ways it could be temporarily sabotaged, e.g. if a child played with it, such as by putting a jumper cap over the Reset header. But if you think it's still in the same condition as the last day it was used, it wouldn't be that.

I don't think it's jumper related. I found limited documentation at https://theretroweb.com/motherboards/s/nec-re … 3,-and-466#docs for the jumper settings. There's also a jumper diagram on a sticker on top of the drive cage outlining factory defaults and what you have to change for various CPU configurations. I even set them to be a known invalid (wrong CPU speed, etc.) to see if I could get something to happen, but nothing did.

Disruptor wrote on Yesterday, 19:52:

Which type of overdrive processor do you have?

The OverDrive processor that came in it is a model DX20DP66. I also eBayed a non-overdrive 486 CPU (A80486D2-66) that didn't do anything either, but I think that requires some grounding of a pin or something maybe to work, though, I don't really know for sure.

One general observation I noticed is neither CPU (DX20DP66 or A80486D2-66) even got remotely warm.

I pulled up a 486 pinout diagram for the OverDrive socket and probed around with a multimeter on some of the voltage pins and got a correct voltage reading where I expected it to be, as well as continuity on the few ground pins I tested. I didn't do a full test of every pin, but there was at least some voltage going to the socket on some pins. I did this after I noticed the CPU wasn't even getting slightly warm upon powering it on.

The board also does not have a traditional looking IC socketed BIOS chip so I can't just remove it to put into my T48 programmer and read the data on it to see if it even has valid BIOS code. The one chip that looked potentially BIOS-like was the one you can see in one of my attached photos with the "A6KS A722" sticker on top of the chip, though, I have no idea, really.

Are those both the same board? The top picture looks much more corroded.

jakethompson1 wrote on Yesterday, 21:53:

Are those both the same board? The top picture looks much more corroded.

Yeah, same board - good catch.

There was a period of a week or so between the first photo and second one while I waited for the second CPU to arrive from eBay. In that period of time, I ultrasonic cleaned the board with Branson 100-955-920 electronic cleaning solution, followed by 99% IPA to displace any water, a good blowout with a DataVac and a day or so wait to ensure it was good and dry.

I did notice there was some general cruft on the board, which is why I ultrasonic cleaned it. I figured it was just from sitting in less than ideal storage. Upon looking at the pre-cleaning photos again tonight, there was more than I recall seeing the first time. I've attached all the photos I had pre-cleaning to this post to show pre-cleaning condition.

Also, there was a dead battery in the system, a Tadiran TL-5242/W, but it did not leak and was still velcro attached in the front of the case, not on the motherboard. At this point, I suspect the cruft means something else is wrong with it that actually did damage, but I have no idea where to start as there seems to be a little bit all over the place.

Attaching the other three corrosion images as I couldn't include them in the previous post due to attachment size limitations.

Those capacitors are similar to a Macintosh LC II era which cause a lot of problems. Don't know if that's part of it, the corrosion too

The corrosion really does seem to be localized around the caps. The early '90s surface mount electrolytic caps were known to leak and cause some major corrosion in lots of electronics, not just computers.

I'm not one of those "recap first and troubleshoot later" kinds of people, but in this case, there's a chance that there are some eaten traces or vias due to corrosion.

lti wrote on Today, 01:56:

The corrosion really does seem to be localized around the caps. The early '90s surface mount electrolytic caps were known to leak and cause some major corrosion in lots of electronics, not just computers.

I'm not one of those "recap first and troubleshoot later" kinds of people, but in this case, there's a chance that there are some eaten traces or vias due to corrosion.

Yea, in any case aluminum film caps might go bad from just prolonged storage without being energized now and then.

Would also systematically examine the board visually for shorts, broken traces, etc, double check all sockets/connections, and at least temporarily substitute that dip switch with soldered bridges corresponding to whatever connections the switch is supposed to do.

If that wasn't enough, the next step would be more scientific methods.

---

Agreeing that what looks like a soldered PLCC32 chip with the A6KS A722 label probably is the BIOS chip. It can easily be desoldered with a regular soldering iron using Chipquik alloy or similar. Would personally install a surface mounted PLCC32 socket instead of soldering the chip back directly when done with dumping/BIOS operations.