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How to read parallel-port POST diagnostic codes?

I usually try desoldering a chip complete first, sometimes they come out real easy and some can be real stubborn, In which case i will slice through the stubborn legs with a small rotary disc cutter (Space permitting) or use a good pair of snips.
 
Trixter said:
I will likely desolder, without regard to saving the original part. I know cutting it would be much faster, but I'd be afraid of damaging the pads or traces, as others have mentioned. I am a total beginner at component-level hardware repair.
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Cutting the pins free from the chip with an abrasive cutoff wheel is actually the safest way to do this. The reason to do it is to avoid the potential stresses on the pads, traces, and holes, when desoldering, which must still be done after the pins are cut.

Desoldering without cutting first is pretty dangerous for someone without a lot of desoldering experience.

I cannot advocate using diagonal cutters or the likes on something like this, though.

An endmill in a milling machine or "pcb router" would actually be even less stressful than a cutoff wheel. But I don't know that anyone ever does that. A cutoff wheel does the job sufficiently.
 
I suggested the Dremel because that's what people know the tool as. My own tool of choice is a Foredom flexible-shaft tool. Not cheap, but with the right handpiece, you can do some very fine work. A dental handpiece would be even better, I suspect.
 
Trixter said:
Tools have been ordered :)
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Perhaps a thread fork is in order, but, I wonder what you plan to use, as in, heat source (soldering/desoldering iron), solder, and solder removal tool.

I see a lot of people insist that you need a temperature controlled desoldering station, but I don't think that is necessary.
 
Trixter said:
On a 6300/M24, if the DMA test passes, you should see something other than 43h on the LPT code reader. If it gets stuck at 43h, it didn't pass the DMA channel test. If it displays 43h, then something else, but no 44h, then the DMA channel check passed but the 1st 64K memory test failed. If you see 44h, you're past that entire section.
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I received the LPT code reader today and had time for a quick test.

When I power up one of the bad 6300 boards the LEDs read 8888. Neither the prev/next buttons on the code reader do anything.

I'll give it a shot on a known good computer (to confirm the code reader works) and on the other 6300 board later and report back.
 
1ST1 said:
If it shows 8888 then the board is completely dead. CPU does not start to run BIOS.
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I think this code reader might be defective. Screen Shot 2016-11-20 at 9.48.24 AM.jpg

I've tested it multiple times on a working 486 and a working Pentium 3 machine - one with award bios, the other with AMI.

Most of the time, it will start up with either 8888 or 88 with 2 of the segments flickering.

Once, I got an FFAA code out of the 486. The documentation that came with the reader is horrible and appears to be for the PCI/ISA post cards. Out of curiosity, how would I read an FFAA code?
 
You can't test with a random different board, they write their post codes to port 80h and not to parallel port. Only Olivetti and a small other number of brands are using parallel port.
 
1ST1 said:
You can't test with a random different board, they write their post codes to port 80h and not to parallel port. Only Olivetti and a small other number of brands are using parallel port.
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Fair enough. Do you know which other machines output POST to lpt? I may have another I can test it with.

I'm still not convinced the card is working properly. Sometimes the power LED doesn't light, but I've confirmed voltage at the parallel port.

I've found specs from multiple sellers on ebay and amazon, they all appear to be the same device, and most claim:

Compliant to the PHOENIX BIOS4.01 ~ 6.01 laptop and desktop
Compliant to the AMIBIOS 6.24, AWARD BIOS 4.51 laptop and desktop
Concrete computer type: IBM, T20, T21, T22, T23, A20, A21, A22, DELL640, TOSHIBA 4030, etc.
Size: 6.0 x 5.5 x 1.5cm

Compatible with the following BIOS chip manufacturers:

ACER - AMI - AST - AT&T - Award - Chips & Tech - Compaq - Dell - DTK - EuroSoft - Mylex - Faraday - HP - IBM - Landmark - Mr. BIOS - NCR - Olivetti - Phillips - Phoenix - Quadtel - Super-Soft - Zenith
 
Trixter said:
If it helps, this is the exact one I tested with my 6300, using a straight-through LPT cable to hook it up (it doesn't quite fit attached directly to the system): http://www.ebay.com/itm/381724918074?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
I used an LPT cable from an old ZIP drive I wasn't using.
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Interesting. I bought this one: http://www.ebay.com/itm/381724919978?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT from the same seller.

He is shipping a replacement to me.
 
Same here. Bought the same unit but it's still in the mail.

WEll at least we can all report back results using the same hardware. ;)
 
I can report back that the second LPT POST code unit works as well, although I couldn't make sense out of the previous/next code buffer buttons -- they didn't seem to display the codes that were sent during bootup. But it did output the correct codes, was very bright, and because of the small form-factor, I didn't need a cable (although I had to place the system unit on its side to read the display).
 
I received the replacement and I have a Toshiba 3200 to test with, which also outputs diagnostic codes via the parallel port.

The defective tester either lights up all 8's or stays completely dark on the Toshiba. The replacement tester logs the codes as the Toshiba boots. By pressing the prev/next buttons it cycles through the codes it logged during boot. On the 6300, the replacement tester stayed dark.

Poking around a bit, I discovered that that the PSU is putting out .83v on the +5 and 3 on the +12 rail. The video power out appears correct at 16 volts. When I'd tested previously, all of the voltages were within spec.

I pulled the PSU and it puts out 5v and 12v when disconnected from the motherboard. I connected an old mfm hard disk to the PSU and it spun up and the voltages were within spec.

I'm going to do some more testing of the PSU to confirm it works under load, and then start looking for issues on the motherboard, bus board and video card that could cause the power issue I'm seeing.
 
So, I've been toying around and here's a simple progression listing for a AT&T 6300 with 640k RAM.
Code: 
<Power switch flipped>
4243
4244
4245
<Onboard dignostic display starts on monitor>
<"All OK" beep> 4648
<Fixed Disk test start> 48A5
<Floppy Disk Drive determined "Not Ready", fixed disk boot> A53F
<End POST>
Many Bothans died to bring us this information, and by that I mean "I dropped the 6300 keyboard on my foot like a klutz while clearing up space to place the diagnostic card somewhere i could record both it and display output with my phone".
 
I think the first half of those codes is just the previous code output, or similar. The actual codes output are only one byte, not two. If we amend what you wrote to account for that:

Code: 
<Power switch flipped>
43
44
45
<Onboard dignostic display starts on monitor>
<"All OK" beep> 48
<Fixed Disk test start> A5
<Floppy Disk Drive determined "Not Ready", fixed disk boot> 3F
<End POST>

...this matches what the POST is actually outputting through LPT1.
 
Hi,

I'm new to the forum, but have found this a really interesting thread.

I've just picked up an Olivetti M24 from my parents house. It worked 5 or so years ago, but is having similar issues to the ones you guys troubleshooting.
Likewise has slight battery leakage (not sure if that is related).
I've also had to replace the Olivetti keyboard with a AT&T branded one from a 6300, so don't know if this would affect boot up.

In my case my CGA monitor starts up and displays
"DMA Control Fail:01"
The computer doesn't boot any further, and no bleeps are heard. The keyboard lights keep flashing.

Reading the thread I've purchased one of the Diagnostic cards to see what codes my device is throwing.
I'm also considering replacing the DMA chip, but I only have a cheap desoldering iron and am not sure whether this is the cause of the issue.

I'll let you know how I get on.

Thanks,

Alastair
 
Welcome to the forums!

The good news is that your board is booting up past the parallel-port POST codes and getting to the part where it can actually display errors onscreen (you probably won't need the LPT POST device). The bad news is that the error message onscreen is very likely what the actual problem is: Either your DMA controller chip needs replacement, or the first 64KB of RAM on your motherboard needs replacement (the DMA test uses the first 64K of RAM to do its testing). Either way, you're going to have to fire up the soldering iron. The "suberror" for RAM failure during the test is 04, but yours is reporting 01 so I think you need to replace your DMA controller chip.

It is ok and safe to use a 6300 keyboard with your M24; that hardware should be identical and only differ in terms of branding. A 6300 system unit and an M24 system unit are also identical except for the BIOS contents (and PAL chips that are paired with the BIOS).
 
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