Wang PC260 issues.

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Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 12:13 pm

Hi all,

I recently got hold of a 1988 286 Wang PC260 IBM compatible computer, with a few issues.

It wouldn't power up, and the PSU would make a buzzing noise. After taking out one of the power connectors on the motherboard, the P8 one, and leaving the P9 one in, I got it to boot. All the voltages seem normal, but only where I've checked.

It reported 640k and 384k of RAM, and then wouldn't boot. No HDD or floppy in the drive. After a while, it started to say 256k of RAM was found, and gave the error of "Memory parity failure at 040000-04FFFF DECREASING AVAILABLE MEMORY" and "Memory data line failure at 100000-10FFFF DECREASING AVAILABLE MEMORY"

Setting the DIP switches on the motherboard to 256k of RAM causes no errors to appear, apart from the BIOS claiming the memory settings are invalid, which I can't change.

Having the turbo button on causes it to only show 64k of ram, and a pile of Memory parity interrupt errors and muddled up text. Can't read half of it sometimes.

Might this be a RAM chip failure? Or something else? Also, what would leaving the P8 connector out do? Can't see any issues, apart from what I've already said.

I'm used to just replacing hot RAM chips in C64 computers, and I have no clue what might be causing this sudden failure.

If you need any more information, let me know. Thanks for taking the time to read this!

EDIT: The system locks up after about 3 minutes too. Just noticed.
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 1:15 pm

The PSU not starting with P8 connected immediately suggests you have a short on the motherboard. This is 9 times out of 10 a tantulum capacitor.
Look at the P8 connector and the wire colors - any pins which would line up with a non-black wire - check their resistance to ground.

Around half of my XT or 286 generation PCs (including my Wang PC-240) needed at least one cap removed or replaced to power up correctly.

The first step for RAM fixing, is to start by re-seating the chips or SIMM modules if used.
Last edited by SpidersWeb on Wed Jul 09, 2014 1:44 pm, edited 1 time in total.
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 1:42 pm

Ah, thanks! I'll do that now.

This computer came with a MFM hard drive, but blew the controller board into halves when it powered up! It was a few tantalum caps that went boom.

There are 2 RAM banks on this computer, Bank 0 is all soldered in, and Bank 1 are all in sockets. Might bank 0 be the 640k and bank 1 be the 384k?

The chips are labeled AAA2801P-07 NMBS. The AAA part might be 444 actually. Can't quite tell. If you'd like photos, I can put some up.
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 1:49 pm

Alright, on the P8 connector, the red cable goes to ground for a few seconds, and the pitch of my multimeter's beeper rises. The yellow cable goes to ground too, but stays there. Blue also goes to ground, at 700 ohms.
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 1:59 pm

If the parts match, it's probably 512/512. Photos would be good, I can't find a single picture of the internals anywhere.

Did the card actually get damaged when they went pop or just make a mess? Because usually after they're gone you tend to find the device still works.
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 2:04 pm

Clym5 wrote:Alright, on the P8 connector, the red cable goes to ground for a few seconds, and the pitch of my multimeter's beeper rises. The yellow cable goes to ground too, but stays there. Blue also goes to ground, at 700 ohms.

Yellow is usually +12V, and red usually +5. But I'm not sure if Wang used a different connector or not (my 240 does). Definitely sounds like you have a short there though.
When it's powered up, can you check the voltages the PSU is spitting out at P8? That'll give us a clue as to which is which.

If you start checking the resistance against each tantalum cap (just across it's pins) you should be able to identify potential suspects. If they read 0 ohms, then they're on the shorted line.
Usually likely suspects will be near the power connector, or near the expansion bus.
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 2:58 pm

Yep, the card was damaged. I've fixed snapped PCBs before, but this one is a little too far gone.

I checked the voltages earlier, and the 5v line was 5 exactly, and the 12v line was 12.20.

I'll check the cable colours again.

After I finish fixing my C64 again, I'll post photos.

Thanks for the help so far!
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 6:19 pm

Here's a link to the photos of the unit, and the output on the screen. If you need any different parts to be shown, let me know.
http://imgur.com/a/gWhmy

Re-seating RAM bank 1 hasn't done anything that I can see. Though, the setup ROM thing is now reporting that I have 1024KB of base memory, which would be 640 + 384. But it now apparently has 15360KB of extended memory! Where'd that come from? POST still reports all the memory errors, and 256k usable.

EDIT: C64 lives again too!
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 8:14 pm

Good work on the C64 :)

Anyway it's these caps that are the likey culprits:
Image
Probably the blue ones too, but I'd guess it's those larger orange caps that are on the +12V line. They're used to filter out noise, which is great until they fail and go short circuit. Being in parallel means you wont be able to find the specific bad cap without removing it from the board first.

What you should do, is identify all the caps on the 0 ohm rail (+12V), then desolder / test and replace where necessary.
What I do, is identify them, then bend each one back and forward until it come soff, until the resistance of +12 increases (usually jumps from 0 ohms to something like 1500 when you get the right one).

So far I haven't had a machine suffer from them being partially removed - not many devices use +12 and those that do usually have their own power filtering. In saying that, if you have the time, putting in new ones to keep it up to spec is desirable.

It's a good plan to do this first, just to make sure the +12 or -12 line feeds are not required for the memory controller (or similar) to operate correctly.

It's a standard AT connector, not the usual Wang setup where there is square plugs. So that plug provides extra grounds, +12 (yellow), -12, and Power Good (the last pin, which nothing pays attention to).

RAM chips looks like the usual array of 41256 or 44256 (not 414256) chips (even if the number is different, I'd wager that's what they are).
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 8:18 pm

Ah, alright. Thanks!

If that works, all I have to do then is get a 3.5" drive working in it. Keeps spitting out a "Diskette drive 0 seek failure" and when I'm using the 5.25" drive, I have no floppies that will work! All of them have a bad track 0 and wont format.

I'll take out those caps now.
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 8:29 pm

And while I can't be sure about the RAM, I had those same errors on my Wang PC-240 - but it uses SIMMs, so I just replaced them (made it a bit easier).
Will need to find a diagnostics tool to identify which chips are failing - if it's just one or two in a bank then you know it's just a bad chip or connection, but if it's the whole bank you have a problem. I usually use the Lansoft/Supersoft Diagnostics ROMs because they require absolutely no memory at all to start up - but hopefully it's easier to find than that.

Floppy drive probably needs a clean :) Around 50% of the 5.25" drives I have arrive have needed the heads cleaned. It should be able to boot off a 1.44 even if it's not set-up correctly - it just needs to be able to read track 0 to get started.
If it's battery is alive, GSETUP (or similar) should sort out the CMOS work fine. You have the exact same BIOS as my IPC AT and Wang PC-240 - so you could probably also get away with using SETUP.COM in here:

http://www.baudband.net/downloads/wang_pc_config.zip

It doesn't list the 260 specifically, but the BIOS version matches my 240.

And don't remove all the caps :P just as many as you need to until you find the right one. Make sure they measure 0 ohms across the leads before snapping too.
Apologies for long rambly posts, I love getting/seeing old PCs back in to life - especially a Wang system.
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 8:40 pm

Thanks again!

The disk and drive I'm using to try boot the 260 works fine in my 486, but not the Wang. Already cleaned the drive, first thing I do!

Long rambly posts are the best posts, especially when it comes to information!

EDIT: Should I still remove the caps that are reporting 100 ohms or so? Or just the 0 ohm ones?
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 9:05 pm

Just 0 ohms. They're connected in parallel, so all the caps on that line will read 0 until you remove the bad one.
Oh and one thing I keep forgetting - remove any expansion cards - I had one occasion a few months back where it was the damn card.

100 somethhing ohms are probably on your +5 line - I usually see around 150 ohms on +5 if I remember correctly.
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 9:13 pm

I'll assume 1.8 ohms counts as 0? Lots of the blue caps are reading 58.8 too.

The only ISA card I have in there is the video card. I have a disk controller and mystery serial card too. I've never worked on vintage PCs before, so my knowledge is a little flaky. I'm used to Commodore computers and such. And still being a teenager, I haven't had the experience of using, and knowing piles about them. I've only been collecting and fixing them for 2 years!
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 9:20 pm

Remember they're in parallel, so the reading you get often isn't for that specific cap but the whole rail.
You want that 0 ohm rail to have a respectable value - anything over a few ohms (although usually it's much higher with nothing using it).

1.8 ohms is ok for a 5 volt rail for example.

5V @ 1.8ohm = 13 watts (if the PSU is still connected - you might actually see that)

Remove all cards. Only remove caps on that 0 ohm line, then come back after and check the resistance of the +12 (yellow) and -12 (blue) after.

I've only been seriously collecting for 3 years, but lord have I learned a lot in that time! I also used to collect/play with machines when I was a teenager as well - it was easier then - replacements were almost free and I didn't have tantalum caps hitting the roof (or my shirt on one occasion).
Last edited by SpidersWeb on Wed Jul 09, 2014 9:39 pm, edited 1 time in total.
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