Built-in "Advanced" Diskette Test vs "Customer" Test

Hardware questions and modifications

Built-in "Advanced" Diskette Test vs "Customer" Test

Postby toddvernon » Sat Mar 07, 2020 6:04 pm

I have been running the builtin tests you get to with the <cntl><alt><ins>

The IBM docs suggest there are two levels of these tests that look alike. One is the customer-level and the other is advanced-level. The only way you can tell is if there is a "6" under the joystick test if its customer level, or an "E" under the joystick if its advanced level. I have never been able to get a "E" suggesting that any tests im running are customer level. [ does anyone know how to get the advanced level? No docs i have found mention this ] (all this was in "IBM PCjr Hardware Maintenance and Service Manual"

To run the diskette test you enter the test by pressing "enter" with the cursor under the test.
Then after watching a funny broken disk animation you put in a blank disk in the drive and enter "MPNP" at the prompt.
The diskette goes through a series of what I think are reads/writes stepping across the diskette (several times).

When the test completes you are back on the advanced test screen and the letter "C" is displayed under the test under the blinking cursor. There isn't any documentation I can find that suggests what "C" means. The manual says its more normal to have a series of 4 digit display here but then a table immediately following that says letter codes may be supplied by the customer. It say a letter code of "C" says there is something wrong with the Cassete? I'm not entirely sure if that table is directly related to the paragraph before.

Anything other than a "*" represents a problem of some sort.

So two questions:
1) How do you get into advanced-tests rather that customer-tests? Perhaps the test plug needs to be installed across the joystick ports? If so has anyone ever seen a doc on how to make that?
2) Has anyone ever seen a document that is perhaps non-public facing that talks about other diskette errors?

The drive appears to act pretty normally, just not working. Thanks for anything you know!

-t
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Re: Built-in "Advanced" Diskette Test vs "Customer" Test

Postby Brutman » Sun Mar 08, 2020 10:44 am

You should look for a copy of the Hardware Maintenance and Service manual; everything is in there.

The manual comes with four plugs:
  • Service plug: Part number 1503441, connects to both joystick ports
  • Post loop plug: Part number 1503442, connects to both joystick ports
  • Serial wrap plug: Part number 1503443
  • Parallel port wrap plug: Part number 8529228

I can pin them out when I get some free time, but honestly I've never used them in 35 years as a Jr owner.
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Re: Built-in "Advanced" Diskette Test vs "Customer" Test

Postby DoctorOctal » Mon Mar 09, 2020 1:57 pm

1) How do you get into advanced-tests rather that customer-tests? Perhaps the test plug needs to be installed across the joystick ports? If so has anyone ever seen a doc on how to make that?


If you have two joysticks, you can get into service mode just by holding down both buttons on joystick 1 (leftmost connector when facing the back of the machine) and the rear (black) button on joystick 2 during the POST. You may want to tape the buttons down.

Otherwise you can fashion your own plug based on the information in the technical reference.

From my notes:

The high nibble of port 201h (which represents the states of the four joystick buttons, Tech ref 2-121) determines the POST mode:

Code: Select all
Nibble  J1B1  J1B2  J2B1  J2B2  Mode
------  ----  ----  ----  ----  ----------------------------------
0000    down  down  down  down  Manufacturing (loop, burn-in)
0001    up    down  down  down  Manufacturing
0010    down  up    down  down  Service (loop)
0100    down  down  up    down  Service
1111    up    up    up    up    Customer


Pin layout, facing back of PCjr: Joystick ports are the two leftmost ports, with Joystick 1 on the left. The joystick switch inputs float high through a 1K resistor and are pulled low (connected to ground) when the buttons are pushed. (Tech ref 2-119, 3-77, 3-78)

Code: Select all
x GND - -   x GND - -
1  2  - -   1  2  - -

x = no connection
- = don't care


2) Has anyone ever seen a document that is perhaps non-public facing that talks about other diskette errors?


As it happens, there’s a document marked “IBM Internal Use Only” that describes the manufacturing and service modes and provides brief descriptions of the error codes you might see in those modes.

Getting those error codes can be helpful if you’re prepared to do component-level troubleshooting and repairs à la Adrian Black. In a few cases there’s a problem you can fix without too much trouble. Otherwise I’d recommend getting your hands on a known working system from which you can borrow the floppy controller and floppy drive to help figure out which you need to replace.
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Re: Built-in "Advanced" Diskette Test vs "Customer" Test

Postby toddvernon » Tue Mar 10, 2020 4:25 pm

Thanks so much for this information! I have been pouring over all kinds of stuff and could not find this! Seems pretty easy to build one now! Really appreciate the reply!
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Re: Built-in "Advanced" Diskette Test vs "Customer" Test

Postby toddvernon » Wed Mar 11, 2020 4:20 pm

Thanks everyone and big thanks to Chuckphd53 for sending me some 3.3 boot disks and other goodies.

I replaced the floppy drive with a Fujitsu M2551A new/old stock. And to my surprise, it didn't work. I had also obtained a floppy card and that did the trick. Apparently it was never the drive in the first place (my money was on the thing with all the mechanical parts). Probably not too surprising as the Jr came with a burned up internal power supply board.
The Fujitsu drive while not authentic is a great drive (and direct drive so no drive belt issues) and literally new (just old). It appears to have a much better build quality so I'm likely going to leave it in (keeping the authentic one of course). Thanks for the help guys!
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Re: Built-in "Advanced" Diskette Test vs "Customer" Test

Postby DoctorOctal » Thu Mar 26, 2020 4:27 am

Correction, for the record: I got the second row of joystick connector pins reversed. The correct pinout for the buttons is:

Code: Select all
x GND - -   x GND - -
-  -  2 1   -  -  2 1

x = no connection
- = don't care
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