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TRS-80 Model II Shugart Drive - Boot Error PI

D

dhoelzer

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Good evening!

I am just completing a few repairs on my Model II (replacing the RAM and SRAM to resolve some flaky chips) and installing a different Shugart 8" SS/DD drive since the other has some extremely fragile parts that I had to repair; the head lock arm is ready to fall off of it.

In any event, the "new" drive is clearly a different model of Shugart, though it appears to be a Shugart 800 which should be correct for this system. The trouble is that I'm now getting a BOOT ERROR PI with a "24" a few lines below that. I can't find any reference to the 24, but the boot error apparently refers to the PIO chip and the suggested fix is to power on the external disks.

I actually managed to score an external drive bay for $100 on eBay, but it won't be here for a week or two. Either way, I'm wondering if this could be solved through termination? I thought I'd ask advice before I start tinkering since this is really my first venture in the TRS-80 world. My plan had been to simply duplicate the jumper settings between the two drives but they are so different that I don't seem to be able to do that. The only settings that I feel confident is definitely important (and the same) is the "DS1" jumper which I'm thinking is a drive select or something similar for the bus.

Thanks!
 
While my experience in the Model II world is very limited, it does spring to mind that there should be a drive terminator plugged into the back of the computer if you aren't using a disk expansion unit.

These terminators are usually lost because once a user purchased a disk expansion unit they lost/threw away the unneeded terminator, but 35 years down the road if you pick up a Model II sans terminator, you can find problems with using the internal disk drive.

My 2c worth.

Ian.
 
With the other fragile drive the system was functioning fine without a terminator block.

TRS-Ian said:
While my experience in the Model II world is very limited, it does spring to mind that there should be a drive terminator plugged into the back of the computer if you aren't using a disk expansion unit.

These terminators are usually lost because once a user purchased a disk expansion unit they lost/threw away the unneeded terminator, but 35 years down the road if you pick up a Model II sans terminator, you can find problems with using the internal disk drive.

My 2c worth.

Ian.
Click to expand...
 
Clearly you know better than I do...

I always believed this device needed to be fitted if you were not using the disk expansion unit:

ModelII-5L.jpg


Ian.
 
Well, I don't know how much I know, but I do know that the other Shugart worked without a terminator. It didn't come with one and booted fine previously. I'm trying to figure out precisely which versions of Shugart drives I seem to have here.

I did track down a document that indicated T3-T6 on a Shugart 800/801 have to be jumped to terminate and I'm pretty sure this is an 800 since I found another jumper on the internal FDC board that is marked "800" and "801" with "800" jumped. The previous drive does not have the same internal FDC board.

I have seen some postings indicating that some number of the TRS-80 FDC/Parallel boards actually used some arrangement that did not require termination but I don't know if that's apocryphal.

TRS-Ian said:
Clearly you know better than I do...

I always believed this device needed to be fitted if you were not using the disk expansion unit:

ModelII-5L.jpg


Ian.
Click to expand...
 
The II terminator pack is a bit odd. To use the external terminator there are a few jumpers on the 800 that need to be set--they won't be on a drive right out of the box.

If you don't have the termination jumper widget, use the terminators on the SA800 PCB should be set. See the directions on page 15 of the SA800 OEM Manual. Remember to remove them if you add the external drive box.
 
Thanks... I'll see if that helps out.

Chuck(G) said:
The II terminator pack is a bit odd. To use the external terminator there are a few jumpers on the 800 that need to be set--they won't be on a drive right out of the box.

If you don't have the termination jumper widget, use the terminators on the SA800 PCB should be set. See the directions on page 15 of the SA800 OEM Manual. Remember to remove them if you add the external drive box.
Click to expand...
 
Well, I've tried adding termination according to the Shugart manual (the new drive turned out not to be terminated internally). Still get the same error.

What's interesting is that it's definitely working to a degree. I know this because the only way you can get one of these past the "INSERT DISK" screen is to actually get it to read a disk. I get all the way through the 64k RAM check and then get the error.

Any other ideas? The disk expansion is still on the slow boat so, if necessary, I can move a drive from that to the main chassis, but I'd really prefer to figure out what's going on here.

fjkraan said:
The terminator pack was only needed for some FDC boards. See http://fjkraan.home.xs4all.nl/comp/trs80m2/FDC_loopback.html and http://fjkraan.home.xs4all.nl/comp/trs80m2/ModelIIBusCardZoo.html.
Click to expand...
 
"Meant for", no, but it is a Shugart 800 which is the same model used in many of these. Additionally, it's pretty strong evidence that it successfully reads the boot sector and completes the RAM test. That -must- come off of the floppy because there's nothing in the eprom except how to read the boot loader. To me this indicates that it is successfully reading from the disk...

If it fails to read the drive it will just spin.. This has the characteristic head load, stop head load for a few seconds, head load for a bit, stop head load for a while during RAM test, head-load again, then the boot error.

Chuck(G) said:
Well, what do you know about the disk? Are you certain that it's good--and it's meant for the Model II or Model 16?
Click to expand...
 
I didn't mean the drive being "meant for the Model II" but rather the disk. Is it possible that the disk contains an error? How have you ensured that it does not have an error and that the content is valid?

FWIW, depending on the floppy controller, it's a fairly simple matter to get the machine to work with a 3.5" or 5.25" HD drive if you don't have an 8" drive attached to a PC to create and check boot floppies.
 
Oohh! Sorry, I misunderstood.

I have several TRS-DOS disks, several of which work on the other drive. They all behave the same way. Successfully begin to boot but then produce the PI error, which appears to be related to the terminator or something directly related.

I think I'm going to have to wait for the disk expansion to arrive to troubleshoot further. Terminating T3-T6 made no difference at all.

Chuck(G) said:
I didn't mean the drive being "meant for the Model II" but rather the disk. Is it possible that the disk contains an error? How have you ensured that it does not have an error and that the content is valid?

FWIW, depending on the floppy controller, it's a fairly simple matter to get the machine to work with a 3.5" or 5.25" HD drive if you don't have an 8" drive attached to a PC to create and check boot floppies.
Click to expand...
 
dhoelzer

Are you quite certain that your 'new' Shugart is in good working order? Anyone in your area that has a Model II that you could check-it out on?
 
dhoelzer said:
I have several TRS-DOS disks, several of which work on the other drive. They all behave the same way. Successfully begin to boot but then produce the PI error, which appears to be related to the terminator or something directly related.
Click to expand...

Sorry for showing my ignorance of the obvious, but are you certain that these are Model 2 (or Model 16) TRS-DOS boot floppies? The Model 2 family does not share compatibility with other models.
 
Really get in there and clean the drive head to eliminate that as an issue. I had a lot of trouble with deteriorating trs 80 disks. Also, make note of the jumpers, if you swap drives re-match the drive's original maze of jumpers assuming you replace with same rev shrugart

Or run away before it is too late! Actually they were hearty machines, but they're all beat up from constant office use, all that boring word processing and accounting ... would make anyone nuts.
 
billdeg said:
Or run away before it is too late! Actually they were hearty machines, but they're all beat up from constant office use, all that boring word processing and accounting ... would make anyone nuts.
Click to expand...

My gripe with them (and with most Tandy boxes) is the flimsy bone-headed construction. Card cage with no guides, flimsy case, no really adequate cooling system. Cards full of ECOs. The Model 2 and 16 were supposed to be the "commercial" systems. That was a joke.
 
Yes, I'm quite certain. i may have mentioned that the floppies previously successfully booted on the marginal drive on the same system.

Chuck(G) said:
Sorry for showing my ignorance of the obvious, but are you certain that these are Model 2 (or Model 16) TRS-DOS boot floppies? The Model 2 family does not share compatibility with other models.
Click to expand...
 
This is a different rev of drive. That's what got me started posting since I can't just match up jumpers.

billdeg said:
Really get in there and clean the drive head to eliminate that as an issue. I had a lot of trouble with deteriorating trs 80 disks. Also, make note of the jumpers, if you swap drives re-match the drive's original maze of jumpers assuming you replace with same rev shrugart

Or run away before it is too late! Actually they were hearty machines, but they're all beat up from constant office use, all that boring word processing and accounting ... would make anyone nuts.
Click to expand...
 
Surely stating the obvious here, but have you tried the original working drive after replacing the SRAM chips and other work you did? It's easy to get ahead of ourselves and chase our tails when repairing any machines, especially the older hardware with 'personality'.
 
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