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maferv
January 24th, 2017, 02:36 AM
Hello guys!

I'm kind of a beginner in the vintage computers world, although I have been using computers since I was very little in the early 90s. I really dig playing with old hardware and software and I like your community very much.

So I got this 286 motherboard. These are some pictures I took plus some info.

3568135682356833568435685

Motherboard and BIOS
Made in Taiwan R.O.C.

In the back it reads:
PCB9060D
E134494
PCBC 9144 FR4

AMI Bios
Sistem BIOS Date: 10/15/90
Advanced System Setup Utility Version 2.32. Copyright (c) 1991 PC Chips INC.
Bios sticker:
COTEK 1988 AMI
286 BIOS

Microprocessor:
HARRIS CS80C286RI787
N9146
(c) INTEL '82 '85 - 20 MHz

Chip:
PC CHIP 4L50F2052
JAPAN 9149EAI
The sticker on top of it reads:
CDCOM
INTERNATIONAL INC

A second chip:
P8042AH 2187
L1184010
Intel (c) 1977

RAM
It's surprising to me that a system can operate with just 640K. I was familiar with 486 systems with very low ram (4-8 MB) but I never had a motherboard with such little RAM. And also, I don't know how this DIP ram works, the way it is grouped is strange to me. I hope somebody can clear this up, please.
I see it has 4 banks of 2 20-pin DIP sockets. And this repeats exactly the same way right next to them. Why?
I also see 4 banks of 2 16-pin DIP sockets, but this aren't repeated. Why?

Which one is better/faster/newer/more advisable to use?

The 8 20-pin DIP memory chips placed in the motherboard read AAA1M304P-07

By chance I noticed that I have exactly 8 16-pin DIP chips in a Hercules card. They read: TMS4164-15NL. Would it be advisable to take them off the card and put them in the motherboard?

Battery:
Panasonic 3/GP60K
3.6V
60mAh

The charge is at 1.45V and it has leaked a bit, and I'm worried about the MB health. I see some corrosion in a nearby component. What is the most recommended (and safest) way to deal with this? Is there a way to use a regular CR2032 button battery?

Thank you very much for your patience and help.

mR_Slug
January 24th, 2017, 07:12 PM
You may be able to find some info on your board here, that will help with ram configuration:
http://www.uncreativelabs.de/th99/

You may have to look through all the pictures and find a board that looks identical but with a different name. PC CHIPS motherboards are a bit hit or miss.

You will have to look up the datasheet on the ram chips you have, but i would guess the "1M" in the part no. means 1Mbit x1. You need 8 1Mbit x1 to make 1MByte. Although in this case you would only have an 8-bit bus to
the RAM, 16-bit is normal in a 286.

I would guess you actually have 1MBytes of ram. 640KB usable, 640-1MB is used for shadowing features. The other sockets are for a different type of ram chip.

The TMS4164-15NL chips are 64kbit x1 @ 150ns, 8 of them gives you 64KBytes. If you did Install them, they may overlap with the ram already installed, and they may be too slow for a 20Mhz system, and it's only 64KB of RAM.

640KB is in most cases the max needed for a 286. The IBM AT came with 256KB or 512KB. Extended RAM beyond 1MB has limited uses, as does the bank-switching expanded RAM.

The battery can be desoldered, or clipped off. Corrosion can be carefully scraped off, and/or traces neutralized with vinegar. The 4 pin header near the keyboard port *may* be for an external battery. If not you can solder
in a new battery, or wires to a battery holder. The coin cells are not rechargeable, so they are not the best option.

Hope this helps.

archeocomp
January 24th, 2017, 09:34 PM
Also there is a list o motherboards here http://stason.org/TULARC/pc/motherboards/index.html

The battery should be removed as soon as possible, so far no big damage is visible.. Clean the motherboard afterwards with (isopropyl)alcohol. The 4-pin connector is VERY probably for external battery
http://www.vcfed.org/forum/showthread.php?35576-3-6v-battery-on-286-motherboard

maferv
January 24th, 2017, 09:59 PM
Thanks for your input. It really does help.

Missing identity:
I've reading many resources and looking all over for info and as you may know, the most common PCCHIPS 286 motherboard is the M-209. Well, it turns out this is a previous version, the M-205.

Just a few moments ago I found the info. I figured it was an older model, so I started googling incrementally: PCCHIPS M200, M201, and bingo...
http://th99.classic-computing.de/src/m/I-L/30426.htm
Incidentally that's a mirror of the website you linked!
http://www.uncreativelabs.de/th99/m/I-L/30426.htm

RAM:
So now I understand better how this kind of RAM works. The smaller DIP, the ones with 16-pin are meant to be used for parity checking, and the larger ones (20-pin long) are the actual RAM. You said the TMS4164-15NL are 150.0 ns and too slow for RAM, but, are they fast enough to be used as parity check? I guess they should be as fast as the RAM, otherwise they would reduce the RAM performance, right? Will it slow down the RAM (AAA1M304P-07 70.0 ns) to 150.0 ns if I activate the parity checking option in the BIOS?

Also, a serious question, why do I need 8 (eight) AAA1M304P to have 1 MB of RAM? Each one of this DIP chips is 128KB?

The battery:

BEFORE
3568635687356883568935690

I also desoldered the battery off the board and cleaned the surface below of it with vinegar, lemon juice and cotton swabs. It's strange to note that not only the coating of a track near the battery got destroyed, but strangely some resistors near the the RAM also were green from the sulfur. And two little pin holes in one RAM socket were green too. But just that. Weird distribution, it seems totally random =S
Doesn't it?

AFTER
356913569235693

So cleaned it, the system boots, and now we're out of danger, right? I was worried about the coating of a track that got damaged, and I read that it is recommended to re-paint it with nail polish. Is that advisable? Or maybe simply covering it with paper or plastic? Please advise.

External battery:

Found the external battery header. But I'm concerned as you just said, is it actually meant for a non-rechargeable battery, or it will blow the CR2032 I'm planning to use? (I got the holder from a now defunct motherboard)
How could I test this? My knowledge in electronics is very limited (but I'm eager to learn) and I couldn't find more specifications of this for this motherboard yet (which by the way, seems to be somewhat of a rara avis).

3569435695

mR_Slug
February 1st, 2017, 01:15 AM
>I guess they should be as fast as the RAM, otherwise they would reduce the RAM performance, right?

Yes, they need to operate at the same speed.

>why do I need 8 (eight) AAA1M304P to have 1 MB of RAM? Each one of this DIP chips is 128KB?

The chips you have are 256K x4. Total bits: 1024kbits/128KBytes See the datasheet here:
https://www.silicon-ark.co.uk/datasheets/aaa1m304p-07%20datasheet%20NMB.pdf

Each of the chips has 4 data pins. The rest are for power and addressing.

One chip alone would give you a 4-bit interface. with 256kwords. (where the word size is 4-bit)
Two chips would give you an 8-bit interface. with 256kwords. (where the word size is 8-bit)
Four chips would give you a 16-bit interface. with 256kwords. (where the word size is 16-bit)

In the two chip setup, as the word size is the same as a Byte, we have 256KBytes of RAM.

In the four chip setup we can state it as having 256KWords (word size=16) of RAM, or to make it simpler 512KBytes of RAM. You have 4 chips in bank 0, and 4 more in bank 1, giving a total of 1024KBytes or 1MBytes.

I hope this explains it.

An alternative memory chip is a 256K x1. Total bits: 256kbits/32KBytes. To get an 8-bit interface you would need eight chips, a 16-bit interface, 16 chips. Since this takes up lots of space the 256K x4 was implemented.

Parity only requires 1-bit for every 8-bytes (in this context). So, an 8-bit interface becomes a 9-bit interface and a 16-bit interface becomes an 18-bit interface. To avoid wasting RAM, on this motherboard, memory with parity
is arranged as:
Four chips of 256K x4 and two chips of 256K x1 per bank.

This gives you 18 data pins. We can state it as having 256KWords (word size=18 ) of RAM, with 2 of those bits used for parity. Or looking at it a different way, 256KWords (word size=16) of RAM plus two additional bit for parity. Or to make it much simpler 512KBytes of RAM with parity protection.

I hope this explains it, sorry if it's a bit confusing. FWIW, i would not worry about adding parity memory.

>desoldered the battery off...Weird distribution, it seems totally random =S Doesn't it?
It sometimes helps to think of it from the perspective of how close components are from an electrical perspective, rather than physical location. The corrosion tends to leach its way down traces. However if corrosion has set in on a trace that has nothing to do with the battery (it just runs near it) now you have a totally different circuit with possible leaching.


>I read that it is recommended to re-paint it with nail polish. Is that advisable?
I have not heard of that, but I guess clear would work. I have used a xylene based insulating varnish for motor windings before, but that's only because I had some. Its also a bit thick so nail polish may work better. Your battery corrosion does not look that bad at all now.

>Found the external battery header...
The external battery header is usually for a non-rechargeable battery, so if you connect a non-rechargeable here there should not be an issue. If you want to solder to the same terminals where the old battery was located then a rechargeable at the same voltage would be the best bet. I doubt you can blow a CR2032 if you try to charge it with a motherboard. I have seen people use a diode to stop the charging, but I have no experience with it myself. Portable telephone batteries are usually rechargeable and have been known to work. But since you have a battery header I would just use that.

maferv
February 18th, 2017, 10:55 PM
mR_Slug
Thank you very much for your detailed response about how the RAM works and all your help.

About the battery:
I placed a CR2032 holder in the same original place the barrel battery (that is to say, the internal battery) was, using the same contacts.

The 4-pin external battery header (CN10) plays an important role here. Through tests and trial and error I found out the following:

Pin 1 is the external battery +
Pin 2 carries 4,6v.
Pin 3 is connected to the internal battery positive (+)
Pin 4 is internal battery/external battery negative (-)

When I got the motherboard pins 2 and 3 were jumped, so that the internal battery would receive 4,6v and so would charge.

I removed this jumper and jumped pins 1 and 3, so now the motherboard receives 3V from the CR2032 button battery and saves the BIOS configuration successfully.

I hope I made myself clear and that this helps any other M205/M-205 owner out there. :clap::computer:

maferv
February 18th, 2017, 11:44 PM
This is how the battery and external battery header look like now:

36309

And I just remembered, the clear nail polish seemed to work just fine.