Early 5150 troubleshooting

[modem7]

Cassette BASIC is sure to be interrogating the BIOS for RAM size, and so for version C1.00 of Cassette BASIC, I expect that you will have seen the displayed "61404 Bytes free" text change to "12252 Bytes free".

Correct. I was charging my phone, so I wasn't able to take a snapshot, and it didn't occur to me to use my mirrorless camera to do the same. But yes, that shows up, but after typing a long string, and ESPECIALLY after typing enter, the system halts with a blank screen and cursor.

In the back of my mind has been the thought that your motherboard may also have a RAM refreshing problem. The symptoms vary greatly, are inconsistent, depend on the RAM amount, etc. And the Supersoft Diagnostic sometimes passes the MEMORY REFRESH TEST.

Some experimentation of mine is shown at [here]. Reading that, you will note that in Cassette BASIC, often the problem is not seen by the user until the time that the ENTER key is pressed. As I mentioned earlier, there is great inconsistency seen, and so one should not look at that web page and come to the conclusion that their motherboard must not have a refresh problem just because their symptoms don't match those on the web page.

 

[modem7]

FWIW, and I think this is when I only set the switch for bank 0, Supersoft passed everything except the floppy controller test, naturally.

That is interesting. I have done lots of experimentation with the Supersoft Diagnostic ROM, and have not experienced that. I have seen weird things like the diagnostic test up to XXX amount of RAM, but if the floppy controller is removed, test up to YYY instead, and it was repeatable. Odd stuff. I'll have to see if I can replicate what you saw.

 

[modem7]

That was the next thing I was going to ask you, actually. I do have my EPROM programmer in hand, so I can do some ROM dumps. Are you able to give a suggestion on how I can do a CRC/MD5 comparison for the files hosted on your site?

In 'HxD Hex Editor' software, I import the BIN file, then on the menu bar, chose {Analysis} then {Checksums}. I can then choose what hashing algorithm I want, including MD5.

 

[pkhoury]

Well, more updates.
Confirmed that the Cassette BASIC ROMS are the same part number. I wasn't able to pull images from existing ROMS, but all works now. Got my 4116 tester today and some NOS 4116's (some had some corrosion on the pins, from having sat somewhere). Got 27 tested out, replaced everything in the computer, populating one bank at a time, and viola, it works!







I guess I'll keep documenting my build here, and when I turn to the other boards to inspect, as noted, they would each get their own thread.

 

[pkhoury]

Another update - put in an IBM 64-256KB RAM card and an AST ComboPlus, along with an early floppy controller (some date codes of 1981) - the Tandom TM100 does a seek after completion of POST and goes into Cassette BASIC. So now it's a matter of ensuring the drive works. As a precaution, I replaced all the tantalums on both the Tandon and the AST with new caps, as well as two new electrolytics for the Tandon motor board.

 

[pkhoury]

I decided I don't have time to fiddle with two different Tandon TM100's, one of which is NOS. I might work with them later. Ended up using a Teac half height, as was found in the 5150 Model B or 5160.

 

[pkhoury]

Last update - put in my replacement EEPROMs. Had some trouble getting them to write, until I got a replacement firmware from the seller for my programmer.
Checksums all verified and now I have the original BIOS revision and ver 1.00 of Cassette BASIC. Also kept my Hercules but outfitted a black bracket CGA card, and just to be safe, replaced all the old tantalums on it. Everything works like it's supposed to, and this computer is now ready to be shown off at VCFSW.




Many thanks to @modem7 for his help getting this piece of history restored!

 

[per]

I cannot answer that, but maybe someone else can. I have not seen any kind of 'ROM failure statistics by make-model' list.

Even if the scope is reduced to ROM's fitted to the 5150 motherboard, the list at [here] suggests a low failure rate. I doubt that a statistically significant sample size of U33/BASIC ROM failures exists.

I can say for sure that I do have had this problem with the MOSTEK 36xxx series, in particular gold cap ceramic ones like the ones here. In my case the set of failing ROMs were from a HP 3456a voltmeter, and dated around 28/29th week of 1980.

 

[modem7]

Many thanks to @modem7 for his help getting this piece of history restored!

And thank you for bringing to my attention the modern MCM68766 substitute (and the modern programmer to program it). Another option for people. I don't think that I would use one though; it looks out of place to me. But that's just me, and just how often does one 'pop the bonnet'. And an XT-IDE card certainly looks out of place.

 

[TWAIN]

I can say for sure that I do have had this problem with the MOSTEK 36xxx series, in particular gold cap ceramic ones like the ones here. In my case the set of failing ROMs were from a HP 3456a voltmeter, and dated around 28/29th week of 1980.

Every 5150 gold-capped ceramic u29 I have ever seen has been bad, including several of my own. Not a statistically significant sample by any means, but certainly frustrating to me…my hunt continues…

 

[pkhoury]

And thank you for bringing to my attention the modern MCM68766 substitute (and the modern programmer to program it). Another option for people. I don't think that I would use one though; it looks out of place to me. But that's just me, and just how often does one 'pop the bonnet'. And an XT-IDE card certainly looks out of place.

XT-IDE has its place, though I'm obviously not using one, since I'm sticking with the original BIOS for a reason. That said, on my XT 286, I fitted it with the DREM, with the eventual future goal of getting every known 286 compatible OS installed into a different virtual hard drive (OS/2, Xenix, DOS, etc).

The modern MCM68766 substitute is still very viable for the PC, though. Though the programmer isn't cheap (bought mine assembled for just under $90, though the PCB and parts are still around $50-70 in total), one could program Supersoft, Ruuds, and finally the BIOS of their choosing easily and simply. I'm sure there are EEPROM solutions for the XT and AT as well, and how often is someone going to pop the bonnet on a machine, anyways?

 

[modem7]

I'm sure there are EEPROM solutions for the XT and AT as well ..

Yes. The Winbond W27E257 is suitable (without adapter) for the IBM 5155/5160/5162/5170 motherboards. It is what I use these days (the nostalgia of erasing EPROM's wore off long ago).

 

[pkhoury]

Yes. The Winbond W27E257 is suitable (without adapter) for the IBM 5155/5160/5162/5170 motherboards. It is what I use these days (the nostalgia of erasing EPROM's wore off long ago).

I might have to consider that for my 5162, only because GSETUP and the IBM BIOS is a pain in the ass. I'd actually been contemplating bringing that to VCF along with this 5150. My goal was to get every major 286 operating system installed on my DREM MFM emulator (and I think I've somewhat accomplished that so far via 86box with Xenix and OS/2).