Wang PC260 issues.

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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 9:34 pm

Ah, now I understand. I can't see any that are dead 0. Rather odd! 002 ohms on the 12v line, and 58 on the 5v line. I guess there must be one somewhere, hiding from me!
Last edited by Clym5 on Wed Jul 09, 2014 10:23 pm, edited 1 time in total.
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Re: Wang PC260 issues.

Postby SpidersWeb on Wed Jul 09, 2014 9:53 pm

0.002 is pretty much 0. If you get 0.002 at the +12 connector, you should get 0.002 on every cap connected over that line. Keep removing those.
Once you remove the right one you should see the readings of the line (and other caps) jump from 0.002 readings to something much higher.

(Sorry if you already got that, just wanted to make sure before I head to bed)
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Re: Wang PC260 issues.

Postby Clym5 on Wed Jul 09, 2014 10:10 pm

I've got one cap on the 12v line reading 2 ohms. 72 watts seems a tad high maybe? After unplugging the PSU completely from the board, the 58.8 caps gave gone to 140.

I meant 2 ohms, not .002! Whoops.

Sorry if I seem like I have no clue what I'm doing. Still used to computers either catching fire, or working fine.
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Re: Wang PC260 issues.

Postby SpidersWeb on Thu Jul 10, 2014 7:29 am

Yeah 2 ohms on +12V without the PSU connected is too high since the machine isn't on.
The PSU will likely start, but that cap (if it is a single cap) will skyrocket out.

Yeah I know how you feel. I've just started up attempting to fix CRT monitors - so used to them either just not working or working fine. With Tantalum caps in PCs I'm fairly sure it's long term storage in less than ideal conditions that shortens the life. Motherboards or cards stored/sealed in original wrapping have been perfect for me so far - not a single pop. Regularly used motherboards etc also the same deal - but you get a rusted XT and pop pop pop.

Hopefully you find the short and get the memory sorted, but if not there is a backup option of replacement. The case/psu looks to be generic, so another generic 286 motherboard could likely be fitted - and you'd still get the WANG message at the top because that's from the video card (which is a good find because mine came with a Wang mono adapter :? ).
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Re: Wang PC260 issues.

Postby Clym5 on Thu Jul 10, 2014 1:28 pm

So I should remove the 2 ohm one then?

I think storage plays a large part in the life of a tantalum too.
This Wang was damp when I got it. Quite rusty, and the most yellowed plastic I have ever seen.

Luckily, I do have a replacement. 486DX2/66 motherboard. That will be a last resort though.

Maybe I'll have more luck with my Toshiba 3200SX!
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Re: Wang PC260 issues.

Postby SpidersWeb on Thu Jul 10, 2014 2:30 pm

Clym5 wrote:So I should remove the 2 ohm one then?

If it's across +12 and GND - then yes. But they're in parallel, so all the other caps on that line will give you the same 2 ohm reading.
It's a case of just finding the right one, and you wont know until it's removed.
I think storage plays a large part in the life of a tantalum too.
This Wang was damp when I got it. Quite rusty, and the most yellowed plastic I have ever seen.

Yes I almost bought it myself as a retrobright experiment :D My PC-240 came from the same seller - it had a single bad tantalum cap near the power connector but no rust. I've seen worse though, my IBM PC, and PC XT's have visible rust on the outside of the case, and my 386 workbox actually has a rust hole under it!
Luckily, I do have a replacement. 486DX2/66 motherboard. That will be a last resort though.

That'll work but if you grabbed a 286 with Phoenix BIOS, you'd never know the difference unless you took the cover off. Postage can be a bit of a pain from the US though.
Maybe I'll have more luck with my Toshiba 3200SX!

T3200SX is a good choice, if anything is wrong with it I likely have spares available (everything except the screen and floppy drive). They are pretty reliable.
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Re: Wang PC260 issues.

Postby Clym5 on Thu Jul 10, 2014 2:55 pm

The odd thing is, I can't find ANY other cap with a 2 ohm reading. It's the uppermost red one, next to the P8 connector. You'll be able to see it in the photos.

Would a smoke test work? Or is that too risky? Tantalum caps can do some damage..

Here's a photo of how bad the yellowing is on the Wang: http://imgur.com/a/iTWfr

There's also that mystery "com card" that came with the computer. Any clue what it is?

Sadly, my only spare unit is a 486. I've got two. A bare motherboard, with RAM and CPU, and a Digital Venturis 466.

Also, do you know of a good way to replace a MFM hard drive without actually using a MFM drive? And if not, where might one be able to get a WORKING one? The last few that I've had have all been dead. Seized, and even if they went, wouldn't read anything. Sometimes, the heads came clean off and stuck to the platters!

I might have to take you up on the offer of parts, apparently this 3200SX wont boot! It's coming up from Christchurch now.

EDIT: After taking the 2 ohm cap out, I'm getting a wildly fluctuating reading of 200 to 800 ohms. Still wont boot with P8 plugged in though. 138 ohms on the 5v line too.

EDIT2: Argh! Now the 12v line has 45 kohms of resistance, and the 5v line has gone up to 241 ohms. I haven't even touched the board since! Looks like I'll be looking for a new 286 board at this rate.

Yet another edit: It lives with P8 now! No clue why, but it does! No smoke yet, and It's been about 5 minutes. Still got the issue with it refusing to use a floppy drive, and the RAM, but at least the PSU is hooked up right!

Another another edit: Everything seems to be slowly coming back to life. Just booted MS-DOS 6.22 from 3 inch floppy.
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Re: Wang PC260 issues.

Postby SpidersWeb on Thu Jul 10, 2014 4:56 pm

Clym5 wrote:The odd thing is, I can't find ANY other cap with a 2 ohm reading. It's the uppermost red one, next to the P8 connector. You'll be able to see it in the photos.

Would a smoke test work? Or is that too risky? Tantalum caps can do some damage..


Check the resistance of the voltage lines again - I'm taking a guess that the pin "blue" would go to also reads 2 ohms to ground. If that's the case, I'd remove that cap.
Personally I prefer to remove than blow - but I haven't seen the kind of damage you describe from the MFM card before.

Here's a photo of how bad the yellowing is on the Wang: http://imgur.com/a/iTWfr

There's also that mystery "com card" that came with the computer. Any clue what it is?

Originally I thought it was just a serial card - but then I noticed it has a Z80 CPU. So one of those connectors is likely a high speed serial port (16450 UART) but the other I have no idea.

Sadly, my only spare unit is a 486. I've got two. A bare motherboard, with RAM and CPU, and a Digital Venturis 466.

I've got that model too - quite a tidy system. I have the matching monitor too "unused in box" from an ex-Digital employee - but it appears it got left in the box because the screen mask was damaged (damn it)

Also, do you know of a good way to replace a MFM hard drive without actually using a MFM drive? And if not, where might one be able to get a WORKING one? The last few that I've had have all been dead. Seized, and even if they went, wouldn't read anything. Sometimes, the heads came clean off and stuck to the platters!

Seizures are an issue when left too long - often the heads seem to become-one with the surface. I've had a few drives arrive seized - if it's the heads and they don't know off easily - you know you're in for a bad time. However "not reading" is quite normal. The logic is on the controller itself - so if you change controller brand/type you usually need to also perform a fresh low level format (writes the sector markers etc) - and even if the controller matches - there is a chance those markers have lost magnetic strength over the last 20+ years and need to be rewritten - which requires a fresh low level format :)

Generally if they spin up and self check OK there is an 80-90% chance a simple LLF will spring them back in to life. I do have quite a few of these, but prying them from me is quite difficult. I just got in an ST277R + controller landed from Ebay US for around $50 though - so if you hunt about you can get a good deal.

Unlike XT's, the AT style computer (286+) has hard drive support in the BIOS and a 16 bit data bus.
So if Winchester isn't of interest - you can just use a normal IDE controller and a matching IDE drive. If the drive doesn't match the built in drive types there are a few options to get around it.
I can definitely help with parts for that just because I have so many - 40Mb to 40Gb. If you wanted to swap that ST225 (assuming it spins up) I could sort you out a big package of tested-goodies depending on what you need/want (sound cards, hard drives, cards, cables etc etc).

I might have to take you up on the offer of parts, apparently this 3200SX wont boot! It's coming up from Christchurch now.

It's probably something really simple like a loose HDD connector, or the wrong drive type was set in the BIOS or someone formatted the HDD. It'll need a new CMOS battery too if it's the one I remember off trademe. I just used a couple of AA batteries in a holder and soldered it to the original wires.

If the drive is dead, I do have a stock pile of Conner IDE drives (which I purposely collect for Toshiba portables). I can't help with a floppy drive though if that's bung.
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Re: Wang PC260 issues.

Postby Clym5 on Thu Jul 10, 2014 5:21 pm

If you wanted to swap that ST225 (assuming it spins up)


After the board blew, I tried spinning the motor on the bottom a tad. every rotation, I would hear 3 clicks, and then the motor would get too stiff to turn.

Thinking it was the end, after the board went, I opened it to find that the heads had come off the arm, and stuck to the disk. No hope. Sorry!

I've got piles of WD400 IDE drives I got from the side of the road, all perfectly working, and some older 800mb IDE disks too, the Wang lacks a IDE port, and my MFM controller card has no IDE port either.

The ones that I had, have been sold a few months ago. A friend's dad needed them for some old computer they still use at his company.

If you want the ISA MFM controller, I'd be willing to part with it. It's a WD1003-WAH.

When I said it wont boot, I meant it wont power on. Whoops.
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Re: Wang PC260 issues.

Postby SpidersWeb on Thu Jul 10, 2014 5:56 pm

Oh it wont power on - that sucks :/

Yeah I have an ST225 that did that exact same thing - I just use it as a display piece now.

For the IDE port you just need a generic IDE / multi IO card - I can''t see any on trademe but I should be able to sort you out something once the machine is started up.
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Re: Wang PC260 issues.

Postby Clym5 on Thu Jul 10, 2014 6:08 pm

I've just been playing BlockOut on it. Going fine apart from constant memory parity interrupt errors, and having 256k of half dead RAM. PSU is making a horrible high frequency whining, but only when the display changes to certain things.

I see this computer has 8 and 16 bit ISA slots. Does it really support 16 bit cards too?

I think I've narrowed down the issues to ram bank 0, as I just took out bank 1 completely, and all the errors are still there. Will piggybacking chips work here? Bank 0 is soldered...

Do you know how many kb each chip will hold? I might have a way of finding the bad chip that way. I can't find much info on the chip.

From the numbers (hex?) it spits out, when it complains about memory errors, might it be possible to narrow it down to a certain chip?

Also, if both banks have 18 chips, wouldn't that mean that, assuming each bank is 512k, the chips are 28.4k each? I'm still confused why the setup BIOS was saying I had 15mb of extended memory. Maybe a glitch?

EDIT: Taking out bank 1 made the turbo button stop crashing the computer. It used to give me 64k of ram and put garbage characters on the screen, and mix up text. Now I've got 256k and no system-crashing errors with turbo on. Just NMI errors that I can ignore. 262144 bytes according to mem.exe.

Time for some new RAM?
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Re: Wang PC260 issues.

Postby SpidersWeb on Fri Jul 11, 2014 8:14 am

286 - yes it takes normal 16 bit and 8 bit ISA cards - sound blasters, network cards, serial ports, anything that fits :)

With the RAM chip size, each chip doesn't hold bytes of data, but rather a bit of a byte. So the 8 bits in a byte get gets spread across 8 chips - then a parity bit (for data integrity) is stored in a 9th chip. If a single one of those fail, that byte of memory is damaged, and you get a parity error. Each chip holds 256Kbits of data.

8x256kbits = 256KB RAM
1x256kbits = 32KB parity data

In my experience, a parity error during the RAM test is usually caused by a faulty parity chip, but a parity error when running the system can be either.
If one of the other 8 chips is failing I usually see a different message. But I haven't had to do this using a Pheonix 3.1 BIOS on a 286 before - usually I only dig that hard for an 8088.

Earlier I wasn't sure how the 286 divided it's data across two rows - but because your memory error kicked off at 040000 (256KB) I would suspect one of the chips in the second row of bank 0 is playing up. Because it's a parity failure, I would usually start by replacing the parity chip (or attempt a piggy back) - this will be either the first or the last in the row.

I have an 8088 motherboard that crashes with the turbo on as well - my plan was to replace every capacitor next to each RAM IC and see if that made a difference - but I haven't done it yet. AST Research (made memory cards back in the day) did release a bulletin saying that some of their memory boards would show an error when those caps failed - which inspired the idea in my head - but without an oscilliscope or actually trying it - I have no idea if it's worthwhile investigating.

The removal of your unused bank improving the situation makes me wonder about power delivery/filtering.
If I was doing an "all in" restore - I'd replace each RAM chip (and install sockets for bank 0) and each filtering cap. But this is quite time consuming.

(This is just my thoughts from my experiences, I haven't done enough 286 memory repairs to be sure, I do have a bunch of dud 8088/286/386 boards - perhaps I should get off ass).
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Re: Wang PC260 issues.

Postby Clym5 on Fri Jul 11, 2014 10:58 am

Ah, that makes more sense. Couldn't quite figure the memory out!

I tried piggybacking chips on the uppermost row of bank 0, to no avail. I didn't get any extra errors though.

Some of the chips from bank 1 seem to be bad though. With some off them, no matter what, I'd either boot with 64k of ram, or I'd get a beep code.that I can't find any info on.

What chip is the parity chip? This is starting to get a bit beyond me!

I've got a scope that I use for ham radio stuff, so I might have a poke around. If I knew where to poke, though.

Thanks for the help so far, at least I can play BlockOut on it!
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Re: Wang PC260 issues.

Postby SpidersWeb on Fri Jul 11, 2014 1:19 pm

It isn't much help, but a reference for your BIOS errors/beeps:

https://groups.google.com/forum/#!searc ... B-W8IT6XoJ

For your messages it basically just says "Try replacing the memory chips" (a little bit basic there!).

The parity chip is the first or last in the row. However according to the link above, the parity error also covers memory errors so it would be any one of them.

It also might not be the chip itself, but a problem with power/signal/PCB or maybe a bad solder joint. It's hard to tell without poking at it myself - but you may be stuck on 256KB (you can get 384KB expansion cards for top-ups) unless you want to replace all those soldered chips + maybe the caps next door and/or check the signal on each pin is what you'd expect (easier said than done sometimes) and check each pin has a good connection to where it should (follow each trace etc).

If you noticed any of them feeling warmer than the others - a bit like on the C64 - that could be an indicator of the problem component as well.
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Re: Wang PC260 issues.

Postby SpidersWeb on Fri Jul 11, 2014 1:24 pm

Oh and side note - I haven't seen the battery yet - where is it?
If it's hidden under the PSU or something it may have leaked.
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