P-Code card won't boot

[jschultzpedersen]

Hi

 

Some years ago when I had my interest in the TI99 rekindled, I bought a P-Code card with Pascal manual and software on Ebay. Unfortunately I had issues with my PEB at the time, and it took  several months to get a working PEB. Then I discovered the P-Code card was a dud. It turned the light on, when booted, but never went further in the boot process. I remember reading somewhere, that a specific batch of cards from TI had that problem - something to do with a diode, that was supposedly easily fixed. The card is of a type, that have no switch to force P-code card boot or a regular boot. Apart from not working it seems to be in excellent condition. I do have another card that works now. But it would be a shame to ditch the card, if it can be fixed. There aren't many out there judging by the lack of offers on Ebay.

 

Does someone know of a fix - assuming it is the diode thing or another typical issue, that I haven't heard about?

 

regards

Jesper

[apersson850]

At least I don't. My card does have the switch, so it's not identical.

[+Ksarul]

If your card doesn't have the switch, it is from the very first batch of p-Code cards TI made for the PEB. The majority of the changes to the board between that and later versions were related to the switch to keep the board from responding automatically. Did you have a p-System disk in your first drive when you tried to boot? I think that version of the card may have hung in the boot process if it didn't find a valid disk. . .and it always looked for the 32K and Disk Controller cards as part of that process.

 

On the version with the diode issue, there was a batch made in late 1982 that had an incorrect diode installed. @arcadeshopper has been working to repair cards from that lot, so he can probably tell you what to look for and what needs to be changed (if anything). That problem may not apply to your card though.

[+arcadeshopper]

3 hours ago, jschultzpedersen said:

Hi

 

Some years ago when I had my interest in the TI99 rekindled, I bought a P-Code card with Pascal manual and software on Ebay. Unfortunately I had issues with my PEB at the time, and it took  several months to get a working PEB. Then I discovered the P-Code card was a dud. It turned the light on, when booted, but never went further in the boot process. I remember reading somewhere, that a specific batch of cards from TI had that problem - something to do with a diode, that was supposedly easily fixed. The card is of a type, that have no switch to force P-code card boot or a regular boot. Apart from not working it seems to be in excellent condition. I do have another card that works now. But it would be a shame to ditch the card, if it can be fixed. There aren't many out there judging by the lack of offers on Ebay.

 

Does someone know of a fix - assuming it is the diode thing or another typical issue, that I haven't heard about?

 

regards

Jesper

Not "easily fixed"

 

what I've found is the 74ls245 goes bad due to the power issue.. it sacrifices itself to protect the rest..   try shotgunning that and/or the 244 and see if that helps

 

another thing is to boot up with the card disabled (no switch? might not be able too) and then enable it in easy bug with the cru bit and then see if you can read the roms in memory location 4000

[jschultzpedersen]

Hi

 

 Thanks for the info. I will acquire a 74LS245 and a 74SL244 and see if I get lucky.

 

Just to be sure as I am not familiar with the phrase... 'shotgunning' means replacing ?

 

regards

Jesper

[apersson850]

According to TI's specifications, you can use the p-code card if you have a box to put it in and a 32 K RAM expansion. That's enough. The card supports executing programs from tape.

If you want to develop something you also need a disk controller and, at the very minimum, a disk drive. If you want to print it supports the RS-232 card with serial/parallel ports.

 

So yes, the card should be able to boot without disks, and even without disk drives. I know from my own card that if I boot with no diskette in a drive, it will simply list that drive as not available. You have to do a new volume scan to find it, once you insert the diskette. If you don't have disks in any drive at startup, so you can't use the Filer to do a volume scan, then you have to use Initialize from the main menu instead.

On the other hand, if the card is in there and the computer doesn't start normally, it must find something on the card. If the card is completely dead, it doesn't have a vaild DSR header, and then it shouldn't run the power up routine either. It's that routine that takes over and boots into the p-system.

[+arcadeshopper]

9 hours ago, jschultzpedersen said:

Hi

 

 Thanks for the info. I will acquire a 74LS245 and a 74SL244 and see if I get lucky.

 

Just to be sure as I am not familiar with the phrase... 'shotgunning' means replacing ?

 

regards

Jesper

shotgunning is the act of replacing all the parts in hope to 'hit the problem' with at least one of them.. that's what a lot of people do with replacing capacitors in a machine, instead of finding the 'bad ones' they just do them all. 

[jschultzpedersen]

Hi

 

Ahh... My english/american vocabulary was just extended. Thanks!

 

regards

Jesper

[+OLD CS1]

19 minutes ago, jschultzpedersen said:

Ahh... My english/american vocabulary was just extended. Thanks!

This will add another for you: back during my ISP days, "shotgunning" was using multiple dial-up Internet connections bonded to increase throughput using multi-link PPP.  We had several users who would "shotgun" two 56k, or whatever speed they could attain, together.  Some people would pay for more than two dial-up connections.  I believe the term was proprietary to either Diamond or USRobotics.

[+mizapf]

It took some time until I understood the meaning of a "shotgun wedding". You have some weird idioms, indeed.

[+OLD CS1]

3 minutes ago, mizapf said:

It took some time until I understood the meaning of a "shotgun wedding". You have some weird idioms, indeed.

'murica.  Land that I love.

[JB]

Shotgun is the perfect word. It can mean anything you want it to.

[+mizapf]

Funnily, although there's a saying like "German has a word for it", I just can't find a proper (well-known) term for a shotgun wedding in German. The closest would be "Muss-Ehe" (Must-marriage), as Google Translate suggests, but when you hear it, you would start to guess what it means and then eventually get to the intended meaning. ("why must? ... ah, I can guess")

[+Ksarul]

 

4 hours ago, mizapf said:

Funnily, although there's a saying like "German has a word for it", I just can't find a proper (well-known) term for a shotgun wedding in German. The closest would be "Muss-Ehe" (Must-marriage), as Google Translate suggests, but when you hear it, you would start to guess what it means and then eventually get to the intended meaning. ("why must? ... ah, I can guess")

Zwangs-Ehe ist etwas näher. . .

[+mizapf]

9 hours ago, Ksarul said:

Zwangs-Ehe ist etwas näher. . .

Not quite, "Zwangsehe" is more like a forced marriage, i.e. forced from outside (literally in this case), as you find e.g. in developing countries where children are married against their will. So if you call it so, this would have some unwanted (and likely inappropriate) ironic notion. 🙂

[+jedimatt42]

Idioms evolve.

 

Shotgun wedding is commonly used to describe haste in a business arrangement. I think usually a criticism, expressing doubt in the merits of the arrangement.

 

That is closer to the use of shotgun to describe therapeutic diagnostics as a repair technique. Hastily swap the chips in sockets, and if the problem goes away, one of the replaced chips must have been the problem. They are both about a hasty decision. Medical professionals exercise therapeutic diagnostics to, but suggesting they are "shotgunning it" would typically be insulting.

 

But traditional use did mean forcing a man to marry a woman, usually to avoid family embarrassment of premarital pregnancy.

[jschultzpedersen]

Hi

 

I did a little exploring. 🙂 'Shotgunning' is also used for a certain way of opening and drinking a can of beer.

 

On a more serious note. I have included a picture of the print. If I understand this correctly I should replace the three SN74LS244N chips near the connector (and cross my fingers as there is no obvious damage the the print anywhere, that I can see. The serial no is: 9021 LTA3082). There do not seem to be any 74LS245 chips on the board.

 

When I boot the system, lights go on for assorted cards in the PEB, such as the 32 K RAM, disk controller card, the disk drive, the RS232  and the P-code card too.  Some are steady and some are flashing. After several seconds all but the RS232 eventually turns off and that is it. I never get the first of several beeps signalling that the p-card is taking over, and the screen remains blank. Everything works as normal with my working P-code card.

[+arcadeshopper]

4 minutes ago, jschultzpedersen said:

Hi

 

I did a little exploring. 🙂 'Shotgunning' is also used for a certain way of opening and drinking a can of beer.

 

On a more serious note. I have included a picture of the print. If I understand this correctly I should replace the three SN74LS244N chips near the connector (and cross my fingers as there is no obvious damage the the print anywhere, that I can see. The serial no is: 9021 LTA3082). There do not seem to be any 74LS245 chips on the board.

 

When I boot the system, lights go on for assorted cards in the PEB, such as the 32 K RAM, disk controller card, the disk drive, the RS232  and the P-code card too.  Some are steady and some are flashing. After several seconds all but the RS232 eventually turns off and that is it. I never get the first of several beeps signalling that the p-card is taking over, and the screen remains blank. Everything works as normal with my working P-code card.

If you can't check the roms with easybug due to it locking up, you may want to pull them and check with an eprom reader/burner  I have a replacement rom solution using a modern chip and an adapter of my design 

 

[+chue]

4 hours ago, jschultzpedersen said:

There do not seem to be any 74LS245 chips on the board.

There appears to be a 245 on the board, but it is not a 74LS.  This 245 (U3 in image below) is next to the card edge connector:

 

[apersson850]

Yes, there must be one, or data can't pass in and out.

[+Ksarul]

The mask ROMs and the eight GROMs are identical to the ones used on the later cards, so functionality should be the same on boot.

[jschultzpedersen]

Hi

 

After some experimentation with the good and the bad P-code card I think I need to try replacing the 244 and 245 chips. By the way - thanks for pointing out I had missed the 245 chip. I only looked for LS codes.

 

With the working card I tested as follows...with the Mini Memory cartridge installed.

Turn the P-card on and boot. Then Halt to get back to the Ti99 boot menu to select Easybug, Then use EasyBug to... Check G1F00 - it reports 01. Then  set it to 01 - light turns on. Then check M4000 - it displays AA. So it sees the ROM.

Then check G1F00 again - it displays 01. Set it to 00 - light goes off. Then check M4000 - value is now 00 (Which I presume means there is nothing there/cannot see ROM.

All in all I assume this is the expected behaviour, and that it works.

 

With the bad card nothing happens. The computer never reach the boot screen or flashes the P-code card light. Awk! I have not soldered since the early nineties. I wonder if my gear still works?! Fortunately, it seems the chips are easy to get and very cheap. So there is room for errors. :-)

 

[+Ksarul]

4 hours ago, jschultzpedersen said:

With the bad card nothing happens. The computer never reach the boot screen or flashes the P-code card light. Awk! I have not soldered since the early nineties. I wonder if my gear still works?! Fortunately, it seems the chips are easy to get and very cheap. So there is room for errors. 🙂

 

It might be a good idea to use some high-quality sockets when you replace those chips. They are the most likely chips to go bad, and if there are ever any problems in the future, changing them out will then be a cinch.

[jschultzpedersen]

Hi

 

Yes, that seems like a good idea to use sockets. I also saw an article in one of the old Millers Graphic magazines, (issue June 1984) that mentioned that it was the mid 244, that was particularly prone to go bad - on the flex cable card, that is. But maybe the same goes for the P-card.

[apersson850]

On 9/2/2023 at 7:31 PM, jschultzpedersen said:

With the bad card nothing happens. The computer never reach the boot screen or flashes the P-code card light. Awk! I have not soldered since the early nineties. I wonder if my gear still works?! Fortunately, it seems the chips are easy to get and very cheap. So there is room for errors. 🙂

If you set the CRU bit 1F00 to one and the LED doesn't go on, then the 245 buffer circuit is at least not the issue. The 245 bidirectional buffer handles the 8-bit data bus. CRU communication is handled by the address bus, CRUCLK and CRUOUT pins. Since they are unidirectional, they go through the 244 buffers.