BOOT ERROR DC on TRS-80 Model II

[Druid6900]

ISTR having that head loading sometimes and sometimes not when doing a drive alignment at some point in my time with Radio Shack and IIRC, it was the index sensor adjustment.

If the alignment on the sensor was out, the head wouldn't load until it was near enough to aligned to get a good signal to the photodetector.

 

[Lorne]

ISTR having that head loading sometimes and sometimes not when doing a drive alignment at some point in my time with Radio Shack and IIRC, it was the index sensor adjustment.

If the alignment on the sensor was out, the head wouldn't load until it was near enough to aligned to get a good signal to the photodetector.

Hmmmmm - that's certainly one of the symptoms I've been experiencing. If the head doesn't load would that cause it to either hang at the Insert Diskette or cause the Boot Error DC message?

Here's another couple tid-bits.
I just booted the Model II three or four times (while trying an unformatted disk - it made no difference), and the second time it got to the BOOT ERROR DC message again (only that second time though).
Another interesting thing is that the In Use LED on the drive, stays on.

 

[Chuck(G)]

Dru--Lorne says he gets the Track 0 indication pretty solid.

Lorne--Do you see the signal on TP21 pulse low when you insert a disk?

If not, does pin 28 on the 1791 pulse high?

If not, when the drive is selected, does pin 32 on the 1791 go high?

If so, do you see pin 34 go low (TK00*)?

Also, double-check the jumpers on the drive, in particular, (2) in the TRS-80 drive documentation:

"A", "B", "C", "Z", "DC", "DS", "T1" and "T2"

 

[Druid6900]

Dru--Lorne says he gets the Track 0 indication pretty solid.

OK, I should have been a little more specific, I meant the index hole sensor.

 

[Lorne]

Dru--Lorne says he gets the Track 0 indication pretty solid.

Lorne--Do you see the signal on TP21 pulse low when you insert a disk?

If not, does pin 28 on the 1791 pulse high?

If not, when the drive is selected, does pin 32 on the 1791 go high?

If so, do you see pin 34 go low (TK00*)?

Also, double-check the jumpers on the drive, in particular, (2) in the TRS-80 drive documentation:

I'll have to check the signals tomorrow, but I do know what's jumpered now.

Here's what's jumpered (as the thing came to me - I haven't moved anything):

800-801 (800 is jumpered)
T1
T2
A
B
DS-HL (DS is jumpered)
Y-Z (Z is jumpered)
DC
C
DS1

EDIT: and T3, T4, T5 & T6 of course.

 

[Lorne]

I'll have to check the signals tomorrow, but I do know what's jumpered now.

Here's what's jumpered (as the thing came to me - I haven't moved anything):

800-801 (800 is jumpered)
T1
T2
A
B
DS-HL (DS is jumpered)
Y-Z (Z is jumpered)
DC
C
DS1

EDIT: and T3, T4, T5 & T6 of course.

EDIT: I checked these a couple times.

The first time, with the INSERT DISKETTE message showing on the screen, TP21 was high before, and after a disk was inserted.
The next time, with the BOOT ERROR DC message showing on the screen (and the head loading for a couple seconds), TP21 was a solid low (no pulsing) before, and after a disk was inserted.

Pin 28 on the 1791 was low before, and after a disk was inserted.

Pin 32 on the 1791 was high with a disk inserted.

Pin 34 on the 1791 was high with a disk inserted.

The above don't sound like that's what we were looking for.
Do they help narrow down the problem?

 

[Chuck(G)]

TP21 is the signal (when low) to load the heads on the drive. When drive select is asserted on the drive, taking the signal at TP21 low will cause the heads to load.

Pin 34, when low, indicates that the drive is on track 0. It will go low whenever the heads are over track 0 and the drive is selected.

Pin 32, when high and the drive is select corresponds to a "drive ready" condition.

Pin 28, when low, corresponds to the complement of TP21. If TP21 is high, pin 28 should be low and vice-versa.

Pin 35, another important signal, should be low briefly (2 milliseconds or so) every time the index hole in the disk is seen and the drive is selected.

 

[Lorne]

TP21 is the signal (when low) to load the heads on the drive. When drive select is asserted on the drive, taking the signal at TP21 low will cause the heads to load.

Pin 34, when low, indicates that the drive is on track 0. It will go low whenever the heads are over track 0 and the drive is selected.

Pin 32, when high and the drive is select corresponds to a "drive ready" condition.

Pin 28, when low, corresponds to the complement of TP21. If TP21 is high, pin 28 should be low and vice-versa.

Pin 35, another important signal, should be low briefly (2 milliseconds or so) every time the index hole in the disk is seen and the drive is selected.

I turned on the machine, and got the INSERT DISKETTE message.
I turned it off, on again, and I got the BOOT ERROR DC message.

While I had that message on the screen, I checked pin 28 again.
Previously, when I had the BOOT ERROR DC message, TP21 was low. Pin 28 is high when the DC error message occurs.

I also checked pin 35 when the DC error message was occurring – it’s high butthe pulse light comes on and there’s a pulsing low tone (under the constant high tone) for about one second when a disk is inserted.


So, it would appear that when I get the BOOT ERROR DC message, TP21 works as it should (low), pin 34 works as it should (low over track 0, high elsewhere), pin32 works as it should (high), pin 28 works as it should (high because TP21 is low), and pin 35 works as it should (pulses when disk inserted).
With everything working as it should, what can be the problem?


I tested the Shugart drive on my bench (with a different jumper configuration of course) using Teledisk, 22DISK, and ImageDisk. The drive works fine – the stepper moves the head to whatever track you select, the drive can make a disk using a Teledisk image, 22DISK can format a disk, and the alignment test using ImageDisk shows no errors.

I’ve also figured out how I can get the BOOT ERROR DC message to occur at will.
If I slightly move the top of the DC board out of its socket, I get the error message, which one would expect when the DC board is no longer connected.
However, this and the intermittent nature of the error have me wondering if it’s just a bad connection of the DC board card into the card cage edge connector, or if there’s a bad solder joint of the card edge socket to the back on the card cage PCB. I wish they’d made these cards insert at the bottom of the case like an IBM 5150 instead of vertically – just seems like you’re looking for potential problems when you try to defy gravity.
Maybe I need to re-flow the joints on that connector?
Is this really a likely possibility, or do the test results indicate a different problem?

 

[Chuck(G)]

Lorne, it's not a bad idea to go over the edge connector joints as well as the joints on the DC card itself. One of the more common issues with 25+ year old systems is bad solder joints. It won't hurt anything and it will eliminate a common source of problems.

 

[Scott Kevill]

Well, at least you've eliminated the drive itself as the cause of problems.

Have you tried cleaning the edge connector pads of the DC board with a soft rubber eraser?

 

[Lorne]

Well, at least you've eliminated the drive itself as the cause of problems.

Have you tried cleaning the edge connector pads of the DC board with a soft rubber eraser?

That I have tried.

I'm resoldering the joints on the four card edge connectors - it's a lot of joints (4 X 80 = 320).
Looks like Tandy was a litlle skimpy with the solder on my board anyway, so it's a good idea.

Next will be all the joints on the DC board.

 

[Lorne]

I have now resoldered the four conectors that the card edge connectors fit into in the card cage.
I've also resoldered all the joints (and there were a bunch of them) on the disk controller card.

I'm still getting the same problem, although I seem to get the BOOT ERROR DC message almost 50% of the time. The other 50% is the INSERT DISKETTE message.

The BOOT ERROR DC message seems to pop up more when the machine has been sitting overnight, and less often after it's started up. It couldn't be something like a cap holding a charge and then discharging it, could it?


I'm almost of the mind to start resoldering everything in the Model II - this thing is driving me nuts.

But, I think I need to back up a bit.
The DC error is supposed to be because of:

1)Defective diskette – try a different diskette
2)Floppy disk expansion unit not on –turn on the floppy disk expansion unit
3)Defective FDC Chip or drive – Contact RSSC


1) Maybe the disk I created from an image is no good - ie: maybe the drive I used to make the image is out of alignment or something else. I doubt it, because when the INSERT DISKETTE message is showing, and I insert a disk, it isn't noticed by the DC, and the heads don't load. The odd time that the heads do load, is when I get the BOOT ERROR DC message.
Just to be sure, Druid is going to send me a known working disk. That'll take care of #1.

2) This one doesn't matter as I've got the drive terminated using T3, T4, T5, and T6.

3) I've checked the drive - it works. It could be something on the DC board, but now I've got the original earlier board, and a later board, and neither of them will work in my Model II. It could be two bad boards - doubtful, but who knows?


If, after testing with the known good disk, I find that it still doesn't work, I think my next step needs to be finding someone with a working model II who wouldn't mind popping my DC card into their Model II to see if it's really my board that is the problem.

If anyone has any other ideas of what it could be, or what could be checked on the DC, please pipe up.

Thanks.


EDIT: ADDITIONAL INFO

Good News - sort of.
I tried the newer version DC again.
From his newer Model II, Kevin Adams provided me some info on the cabling for that newer card.
I made a cable, connected the card to the drive, and removed the jumpers at T3, T4, T5 & T6 (the newer card doesn't need termination on the drive).
Turned it on, got the INSERT DISKETTE message, inserted a disk, and then got the BOOT ERROR DC message.
And that's what occurs every time now ! (No more just hanging at INSERT DISKETTE).
So, maybe it is the disk I made from an image.
We'll have to wait and see. (hey Druid, hellooooo ?)

 

[Druid6900]

We'll have to wait and see. (hey Druid, hellooooo ?)

Oh, first it's don't worry, take your time and now it's "hellooooo"? LOL

I'll fix either the Model 12 or the 16(a) tomorrow and make you up a tested diskette and get it out to you. After that, I'm tearing them and the 16B down and parting everything out since no one seems to want the whole machines.

 

[Lorne]

After that, I'm tearing them and the 16B down and parting everything out since no one seems to want the whole machines.

I think that's a helluva idea, especially seeing as I might be needing a working FDC !

 

[kb2syd]

I think that's a helluva idea, especially seeing as I might be needing a working FDC !

16B FDC is built into the motherboard.

 

[Lorne]

16B FDC is built into the motherboard.

It's the "them" I may want the FDC from (not the 16B).

 

[kb2syd]

I missed the them.

 

[Druid6900]

In actually fact, the 16(a) is the only one that has a discrete FDC board, the other two (12 and 16B) both have them built into the motherboard.

 

[MikeS]

... I'm tearing them and the 16B down and parting everything out since no one seems to want the whole machines.

Hoo boy, I hope Trixter doesn't read this, especially at your prices ... ;-)

 

[Druid6900]

Hoo boy, I hope Trixter doesn't read this, especially at your prices ... ;-)

Yeah, I'm trying to make as much money per year as a pampered programmer did LOL