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Model 25 won't boot

E

evildragon

Veteran Member
Joined
May 29, 2007
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Location
Tampa Florida
Ok, I come home today to use my model 25, which I do my banking on (yep, I like the simple ways of banking on it than the cluttered mess on my modern systems)

And instead of the normal count RAM post, I was only greeted with the blinking text cursor, and nothing else. (well, almost. the VGA hack, the VGA signon message did show, but that was it, nothing else).

I reseated the drives, video and sound card and CPU. I even removed the VGA card hack and went back to the onboard MCGA, and same thing.
 
Meeps? Beeps? No error number or anything at all? Using the original processor or did you upgrade it?
 
Well, you had a cursor and a welcome message from the VGA controller, so it can't be that sickly.

Here is the part where you pull out your technical reference manual, your Sams ComputerFacts (for your machine), some spare known good adapter cards, a multi-meter and a static strap and start to do some debugging ...
 
mbbrutman said:
Well, you had a cursor and a welcome message from the VGA controller, so it can't be that sickly.

Here is the part where you pull out your technical reference manual, your Sams ComputerFacts (for your machine), some spare known good adapter cards, a multi-meter and a static strap and start to do some debugging ...
Click to expand...
Of which I only have 3 of the things mentioned, static strap, mulitimeter, and spare known good parts..

This is what I have tested/swapped:
Swapped RAM for good: No change
Went back to onboard MCGA: Has cursor, that's it.
Empty ISA slots: No change
Original good CPU's: No change
No drives attached: No change

So far, resistors look good (though hard to tell when in circuit).

My friend is right now as I type this, coming back from a local part store with EEPROMs, and will use her EEPROM programer and try re-burning the BIOS, as I made a backup one time via your app. Decided to do the BIOS bit first since it's on a socket. Nothing seems burned...

EDIT: Ok. Before burning, she dumped the BIOS chips with her programmer, and compared it to the checksum of the backup from before. They are indeed different, so the BIOS is perhaps to blame? She burned the original BIOS to two EEPROMs, and now the CRT just has no sync. The EEPROMs are good however, tested before put to use. She's reading the manual to her EEPROM programmer right now...

EDIT: She had to use a certain switch to change the order the bytes were burned in apparently. She burned it again to both chips, replaced in socket, and now the Model 25 is booting up to my Win 3 desktop..

So, how often do ROMs just fail like that? My Model 25 actually came from IBM on EPROMs. (it had a silver sticker over the window)...
 
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I would take this opportunity to get the technical reference manual and any other documentation for when the next problem happens. It is very difficult to debug a machine without some sort of documentation.

Second, something smells fishy about your Model 25. I have never seen an IBM machine 'from the factory' that used an EPROM for the ROM BIOS. They have all been burned ROMs unless it was in a prototype. Given the quantity of Model 25s that were produced, a burned EPROM doesn't make any sense.

You should find somebody else with another Model 25 and compare BIOSes. Somebody most likely modified yours.
 
mbbrutman said:
I would take this opportunity to get the technical reference manual and any other documentation for when the next problem happens. It is very difficult to debug a machine without some sort of documentation.

Second, something smells fishy about your Model 25. I have never seen an IBM machine 'from the factory' that used an EPROM for the ROM BIOS. They have all been burned ROMs unless it was in a prototype. Given the quantity of Model 25s that were produced, a burned EPROM doesn't make any sense.

You should find somebody else with another Model 25 and compare BIOSes. Somebody most likely modified yours.
Click to expand...
My father got my Model 25 right out of the box back in 87. I was only 1 years old then, but I do remember it "a little".

Most chips in my model 25 were all ceramic package. The nmos chip, 8086, BIOS, they were all ceramic. Serial number is a bunch of "6" (yea, scary)..

http://blackevilweredragon.spymac.com/xt16/2.jpg
(There used to be a silver sticker over those chips. I foolishly uncovered them, and this seems to be what killed it, along with my friends backlight in the same room)

Note the EPROM BIOS chips, and the ceramic nmos chip (ram DAC??).. All chips are standard.

Other Model 25's I checked do indeed use regular pastic chips, and a ROM chip. But, when I have compared the BIOS with MD5 hashes (before my BIOS died), and it was the same. Remember the thread asking about a newer BIOS rev, and finding out they were exactly the same? Yea..

Would be cool if my Model 25 was a proto, but I doubt it. I do know though it's a VERY early unit..

EDIT: Here's what the sticker on the front says.
TYPE: 25-001
S/N: 88-26666

Hopefully IBMMuseum will come by and verify with his Model 25's, if any of his have EPROM's for BIOS chips, on early units.
 
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mbbrutman said:
I have never seen an IBM machine 'from the factory' that used an EPROM for the ROM BIOS. They have all been burned ROMs unless it was in a prototype.
Click to expand...
IBM sometimes used EPROMs in the 5160 and 5170.

In the 5170, there are PROM and EPROM versions of the final BIOS (11/15/85).
Different part numbers are found on the top of the chips, and IBM changed the contents of the EPROMs to reflect the different part numbers.
They also had to adjust the final byte in one of the EPROMs so that the checksum became 00.
PROMS: 62X0820/62X0821
EPROMS: 61X9266/61X9265
A picture of both sets is at http://members.dodo.com.au/~slappanel555/misc/5170_ROM.JPG

Later, when the final BIOS (05/09/86) was created for the 5160, both PROM and EPROM versions were created.
The contents are the same but IBM use different part numbers on the top of the chips.
PROMS: 62X0890/68X4370
EPROMS: 59X7268/62X0819
Within the ROM for position U19 is the string, "62X0819=68X4370 59X7268=62X0890".

So why did IBM use EPROMs? Cost? PROM supply shortages? I notice that in the 5160, the EPROMs used by IBM were 100nS. IBM could have used 200nS chips, and so that suggests that cost wasn't the reason.

ROM failure on old motherboards appears to be fairly common. Since becoming a member of these forums a year and a half ago, I've seen about 5 threads where the failure of a 5150/5160/5170 motherboard was due to the ROMs. In fact, only a fortnight ago, the faulty 5170 that dkedrowitsch wrote of (http://www.vintage-computer.com/vcforum/showthread.php?t=9601) had a faulty EPROM - offline we compared the checksums to known good ROMs and determined that his 61X9265 EPROM has corrupted contents.

In case you don't know, a crude test to check the validity of the ROMs in the 5150/5160/5170 is to calculate an 8 bit checksum.
For the 5150, the 8 bit checksum of U33 should be 00.
For the 5160, the 8 bit checksum of the combined U18/U19 should be 00.
For the 5170, the 8 bit checksum of the combined U27/U47 should be 00.

Eg. 61X9266 (U27) = 10 , 61X9265 (U47) = F0 ---> 10 + F0 = 00
 
I do MD5 hashes right from a programmer. That's sorta what I meant by "checksum".

I'm now using an EEPROM instead of an EPROM. Will there be any difference? I believe my friend had to do something to the chip to get it to work. Not sure what though.
 
Hmm .. Learned something new again.

All of the IBM systems that I've ever peeked inside of used burned ROMs, not EPROMs. When producing anything on a large scale, ROMs make more sense. It would be interesting to know what drives the choice between the two ...

Mike
 
Ok, lesson learned.

Cover IBM when black light is in use.

EDIT: Oh wait, since EEPROMs are now installed, I wouldn't need to worry about that. But then again, VGA card has same thing, EPROMs, so I guess I still should cover IBM anyway.
 
You should cover the EPROMs anyway, black lights or not. Covering them guarantees that nothing stray is going to get it.
 
Ok, put electrical tape over the two chips.

Btw, my friend bent a pin, and soldered it to a different pin on the new EEPROM she used for my 25's BIOS. What is that? It seems like a hack, but she keeps insisting that it has to stay in order to be readable..

I tried searching, but couldn't find anything... And my friend isn't available right now for answers, I'm at my mothers house atm..
 
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mbbrutman said:
Hmm .. Learned something new again.
Click to expand...
Same here.
I had always thought that with the first revision BIOS for the 5160, that both ROMs were 32K in size but that in U19, only 8K was used.
It turns out (according to the 5160 Tech. Ref.) that U19 on the 64/256K motherboards (the motherboard where the first BIOS was used) is in fact an 8K ROM. In the move to the 256/640K motherboard (where the second BIOS was used), U19 was upped to a 32K ROM.
 
evildragon said:
Btw, my friend bent a pin, and soldered it to a different pin on the new EEPROM she used for my 25's BIOS. What is that? It seems like a hack, but she keeps insisting that it has to stay in order to be readable....
Click to expand...

Most likely she had to use a substitute chip and one of the pins had to be tied either high or low to enable a chip read function. It's fairly common when trying to replace a chip that isn't readily available any longer.
 
Druid6900 said:
Most likely she had to use a substitute chip and one of the pins had to be tied either high or low to enable a chip read function. It's fairly common when trying to replace a chip that isn't readily available any longer.
Click to expand...
ok, as long as it's safe to the 25, im alright with that..
 
evildragon said:
...Hopefully IBMMuseum will come by and verify with his Model 25's, if any of his have EPROM's for BIOS chips, on early units.
Click to expand...

All of the Model 25s (at least the 8086-based version) I've seen use "OTP" (One Time Programable, meaning it has no erase window at all) PROMs. Some early PS/2 models (mainly with a 40-pin EPROM, so Model 25 286/Model 30 286) will use an EPROM with an amber-colored transparent sticker over the window. And as commented before, the 8086-based Model 25 only had one BIOS version, with no after-factory replacements I know of (meaning all should be the same arrangement of code and checksum).
 
Yea, all BIOS is the same, I know that after trying it out.

Thing is, my BIOS chip did come from IBM as EPROM's, but it's an 87 model, very early, so perhaps something was up then. My planar is different overall, than the other 25's I've seen and used. Layout is different too for some parts.

My EPROM from the 25 looks exactly like the previous poster, same intel chip type..

http://blackevilweredragon.spymac.com/xt16/2.jpg

That picture was taken some time ago. Those EPROMs are the ones that were in my 25 when my father took the IBM out of the original box when he bought it in 87. Matter of fact, they've NEVER been moved from the socket till yesterday. It's a pitty a few years ago I ripped the sticker off foolishly.
 
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I don't think he means he dials in to his bank/logs on to it. I think he means something quite simple like I do: Using Microsoft Works 3.0 for DOS, I create spreadsheets and charts of my finances. For that sort of stuff, it is rather self-explanatory if you know or have a reference sheet for the formulas. Although, since recently switching to an IBM 5150 w/out a HD, I use Reflex software. I could make a copy of it and/or multimate if anyone would like. I have been looking into doing banking on a 486, online. It should be rather simple. Install the correct drivers for your modem or NIC, and install a program of some sort that can access the net. Or get an old version of Microsoft money or some other banking software, and give it the parameters for your bank. But that's just theory. I haven't done it yet so I can't say for sure, just like I don't know for sure evildragon didn't mean he does online banking on his Model 25. I want one of those pretty bad. I have the DOS disk specifically for one...

--Ryan
 
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