Leading Edge Model M – POST beeps (graphics card?)

[Cosi]

Howdy.

I'm trying to get my newly-acquired Model M running. So far it's been going good: I've installed an ATX PSU (the M has an exotic power connector, which turned out to be a bunch of "molex" pins protruding directly from the motherboard), the FDD is also working (tested with another machine). Eventually, I got stuck at installing the graphics card.

It's a Trident TVGA9000C. When I set the SW1 switch on the motherboard to "RESERVED" (EGA), I'm getting 1 high-pitched and 5 low-pitched POST beeps, regardless of whether the card is installed or not. When I change the setting to "Color" or "Monochrome", beeps change to 1-4 followed by 1-7.

I checked the code of the Model M BIOS (both 3.30 and 4.71, dumps found on the Internet), and it seems like 1-5 might have something to do with the graphics card: the routine tries to write 8000 bytes to b800:0000, read them, and compare the output with what has been written. If I'm not mistaken, this would suggest that the computer doesn't see the card at all.

So, I've found a discussion where someone presents a mod enabling the Trident to work with a PC 5150. Should I attempt to do that mod and see if it helps, or maybe there is something I should try first?

Thanks for the help.

 

[Cosi]

UPDATE: I did the mod and I didn't fry the motherboard but it didn't help either.

 

[modem7]

Welcome to these forums.

I do not know about the model M specifically, however, I can provide the following information.

For a motherboard to support an EGA or a VGA card, the motherboard's BIOS needs to support BIOS expansion ROM's (a.k.a. BIOS ROM, option ROM, boot ROM, etc.)
If I look at the two 'Leading Edge' entries on the web page at [here], I see that version 3.30 of the motherboard BIOS does not support EGA, let alone VGA.
Is it version 3.30 that you have on your motherboard ?

 

[ldkraemer]

The Leading Edge Model M did not support EGA, but there was an updated BIOS that did
support EGA. I've purchased it, and used it along with two of my buddy's.

The Sperry HT BIOS 4.71 does support EGA, and was the One I purchased.

Ray (modem7) should have a Copy on his site, as I forwarded it to him.
If he doesn't, send me a DM and I'll forward you the file.

I have some other clock setting utilities you also might need/want.

Plus, you need to cut out that battery for the clock and replace it.
You will be lucky if the PCB traces aren't destroyed.


Larry

 

[Cosi]

modem7: Thanks for the reply.

Honestly, I have no clue how to check the BIOS version, I only have the seller's word who asserted that the machine works with ISA VGA cards (and that he had tested it with one such card).

Curiously, *both* versions of Leading Edge BIOS have this routine (the code is almost identical), so perhaps it's either a test carried out before the computer attempts to recognize the card, or I've misread the code.

ldkraemer: I already have both dumps. The problem is, I don't know how to check the version my M has.
I assume I should get myself an EPROM programmer if it turns out that I have an outdated version...

 

[modem7]

I only have the seller's word who asserted that the machine works with ISA VGA cards (and that he had tested it with one such card).

With the seller having successfully tested a VGA card in your computer, that certainly suggests that the motherboard BIOS must be a later one, one that supports BIOS expansion ROM's.

But not all ISA VGA cards are going to be compatible with the Model M. 16-bit VGA cards can be problematic in an 8-bit computer. For example, we know that some 16-bit VGA cards do not work in the IBM PC (IBM 5150), and the web page at [here] was created to document what is known to work in the IBM PC. Same thing for the IBM XT (IBM 5160). And there is at least one 16-bit VGA card that works in the IBM XT, but not the IBM PC.

It's a Trident TVGA9000C

But is that an actual Trident TVGA9000C card, or a non-Trident card that has a Trident TVGA9000C chip on it !!!
One may work, but not the other, because of hardware and/or software reasons.

I checked the code of the Model M BIOS (both 3.30 and 4.71, dumps found on the Internet), and it seems like 1-5 might have something to do with the graphics card: the routine tries to write 8000 bytes to b800:0000, read them, and compare the output with what has been written. If I'm not mistaken, this would suggest that the computer doesn't see the card at all.

Curiously, *both* versions of Leading Edge BIOS have this routine (the code is almost identical), so perhaps it's either a test carried out before the computer attempts to recognize the card, or I've misread the code.

B8000 is where video RAM on a CGA card starts at.

If I look in the BIOS ROM for the IBM PC and IBM XT, I will find similar code. But that code does not always get executed. It only gets executed if I set the motherboard video switches to the CGA setting. With the switches set that way, the power-on self test (POST) is expecting video RAM starting at B8000 (i.e. CGA video RAM), and tests that RAM. If the RAM does not exist, or is faulty, the POST reports an error. For the IBM PC (IBM 5150), you can see that as step 20.1 in the web page at [here].

 

[Cosi]

That's too many unknowns for my head!

In the meantime I sent the EPROMs to a friend for dumping and upgrading if necessary, so I can't test it now, but I'm pretty sure I've checked all the documented SW1 combinations. There's one setting that – in theory – should be selected for an EGA card (obviously; there were no VGAs at that time) *if* the BIOS has been upgraded to handle it. For that setting (and, IIRC, CGA 80x25) I'm getting 1-5 beeps. For some other settings (Hercules, perhaps also some random combinations) it's 1-4 followed by 1-7. According to the Model MH documentation (!), 1-4 means keyboard self-test error (and rightfully so, as I don't have a keyboard connected at this point) but, curiously, there's no such code as 1-7 (I couldn't find it in the code either).

However, I beg to differ regarding B8000 (B800:0000): apart from being used by CGA, it's also used for EGA/VGA text mode (as described here). This may have nothing to do with the M's POST code (that routine can be found both in the upgraded BIOS and in the original version) and I might have had misconfigured my video, though. (In the docs that Larry has shared with me there's a mention that the manuals circulating on the Internet are wrong about the switches responsible for video configuration – it should be SW2 instead of SW1, IIRC.)

Anyway, when my BIOS comes back, I'll get you updated. As I mentioned to Larry, my motherboard differs a great deal from the ones I've seen on the Internet, so maybe I have some exotic BIOS as well (two EPROMs!)..?

But is that an actual Trident TVGA9000C card, or a non-Trident card that has a Trident TVGA9000C chip on it !!!

Ha, that's a good question! This is my card (the mod is on the backside and can't be seen in the picture):

https://imgur.com/a/mRYkcDh

Its layout differs from the other models I've seen, so maybe it's a clone..?

 

[modem7]

However, I beg to differ regarding B8000 (B800:0000): apart from being used by CGA, it's also used for EGA/VGA text mode (as described here). This may have nothing to do with the M's POST code (that routine can be found both in the upgraded BIOS and in the original version) and I might have had misconfigured my video, though. (In the docs that Larry has shared with me there's a mention that the manuals circulating on the Internet are wrong about the switches responsible for video configuration – it should be SW2 instead of SW1, IIRC.)

Yes. Unless the motherboard BIOS is properly disassembled to discover exactly what it is doing, we are simply making 'educated guesses'. Clones are never 100% clones.

A bit like discovering clones of the IBM PC that do not use the 'twisted' floppy cable that an IBM PC does.

Ha, that's a good question! This is my card (the mod is on the backside and can't be seen in the picture):

Its layout differs from the other models I've seen, so maybe it's a clone..?

Take a look at the photo at [here], which is of a card that I own (or had). I didn't do a detailed examination, but it looks to be the same card as yours, except that different RAM chips are used. My card only works in my AT-class computers.

I put the 'Operating Instructions' document, and support diskette, at [here]. In the instructions is, "8 or 16 Bit AT-Bus Slot Select", but notice the specific use of "AT-Bus". I haven't tried the 'ALE mod' that you referred to in post #1.

 

[Cosi]

The mod is really simple and reversible, and several people have reported that it works – but, like you said, a clone will never be a 100% clone. There's an interesting (albeit very technical) thread about differences between IBM PC and XT, and XT vs. XT clones wrt. the ALE signal and compatibility with the Tridents.

 

[Cosi]

It lives! I can put it here for the posterity: modded Trident TVGA9000C cards do work with Leading Edge Model M computers with BIOS v4.71N

Interestingly, it looks like the 1-5 beep sequence is really 1-(4+1) – the M still beeps on startup, but when I enable "detailed self-test", it makes a noticeable pause before the last beep. So, either keyboard or the RTC, I presume.

Slightly off the original topic: the computer came with a TEAC FD-55GFR disk drive in excellent condition (the heads literally shine) and, surprisingly, it works with both the M and my 386 with the same jumper configuration (DC, LG, IU). However, the M can't read 360k diskettes at all (even those formatted with this FDD) – I'm getting "address mark" errors upon boot even though the 386 can easily read them. It has no problems with 1.2M floppies, but I only have two of these and they're apparently corrupt (?) and can't be properly initialized.
I'm considering buying a couple of brand new, unused 1.2M floppies (which, I hope, would be the ultimate test for the FDD), but I don't want to ruin them with a misconfigured drive. Is there something I should check/do beforehand? (I've already tested head alignment with ImageDisk and all seems to be fine.)

Thanks

 

[rlauzon]

Honestly, I have no clue how to check the BIOS version, I only have the seller's word who asserted that the machine works with ISA VGA cards (and that he had tested it with one such card).

My Sperry HT (which is supported to be a Leading Edge Model M) has a program called ROMVER that prints the version of the ROM.

 

[Cosi]

@rlauzon Will you mind sharing that program? There's an archive of the old Leading Edge BBS, but I couldn't find the tool you're talking about there. Thanks!

Tbf. when I posted that, the old BIOS prevented me from starting the computer at all (or even getting anything printed to the screen, for that matter), so the only way to find out was to dump the EPROMs and look inside the dumps

 

[ldkraemer]

I found that Program on my Old Hard drive image. I think my Leading Edge Model M had
version 2.1 and I upgraded to DOS 3.3. But, I might be mistaken.

Larry

 

[rlauzon]

@rlauzon Will you mind sharing that program? There's an archive of the old Leading Edge BBS, but I couldn't find the tool you're talking about there. Thanks!

Here's the version from my system.

 

[Cosi]

Thanks, guys!