• Please review our updated Terms and Rules here

Issues reading disks on Kaypro 2/84

retrobecanes

retrobecanes

Experienced Member
Joined
Apr 11, 2017
Messages
145
Location
Florida
My recently acquired Kaypro 2/84 doesn't seem to be able to read disks, where they are from the two original disk drives or from a Lotharek SD Floppy emulator. In both cases, I just see the message to enter a floppy in disk A. The physical drives spins, the head sometimes moves a little but nothing else happens. No error message, nothing. With the Lotharek, I load a CP/M image but the computer remains on its 'insert a floppy in drive A' message. What else could I try? I checked the RAM and all the chips seem okay.
 
Someone should come along that will be able to help you much better than me, but my question is, do you know you have both a good bootable disk that is the correct one for your model?
 
alank2 said:
Someone should come along that will be able to help you much better than me, but my question is, do you know you have both a good bootable disk that is the correct one for your model?
Click to expand...

As I am brand new to the KayPro it is possible that I am not using the ideal disk image. When it comes to the physical drives, I was using the floppies that came with the machine. None of them seemed to work (not even an error message on the screen). I then decided to connect my Lotharek (HCX) SD Floppy Emulator with some of the 2 and 2X disk images that I found on the web (.TD0, converted to .HFE) but then again no luck (no apparent search or activity on the emulator screen). I know that my KayPro is a 2/84 with an 81-292 ROM. Could someone point me to a .TD0 image that should work with that model?
 
With the 81-292 ROM, any *detected* disk errors should result in a "I cannot read your diskette." message on the screen and then it halts (you must RESET to try again). 2.2G is the correct CP/M image, provided the boot tracks are not corrupted (even online diskette images have found to be corrupted on occasion). Given you've tried with real floppy drives and an emulator, seems like the problem is either on the Kaypro mainboard or an excessive amount of bad luck with images.

The two main reasons that 81-292 will just be "stuck" at the "Place your diskette in drive A" banner are that 1) the drive never appears READY (has no diskette inserted), or 2) the loaded boot image is invalid/corrupted.

For (1), a place to check is the circuitry that brings in the drive INDEX pulse. Maybe make certain that the FDC 1793 INDEX pin (/TP, 35) is pulsing (when the drive has a diskette and is spinning).

For (2), it seems like the problem would have to be on the CPU side of the FDC 1793 (including FDC 1793 bus drivers or internal registers), as any corruption of the data signal from the drive should result in CRC errors. Or else your diskette images are not good.

Unfortunately, an explanation for both (1) and (2) is that the FDC 1793 is bad - it is a very scarce part.
 
Hi Durgadas311, I placed a check on pin 25 of the 1793 and I do get a pulse when I load a disk image in the emulator. When I "eject" the disk image, the pulse stops.
Most of the disk images that I find for 2.2G seem to indicate ROM 21-292A while mine just says 81-292. Is that okay?
Also I see some 2.2G images in SSDD and others in DSDD, which one should I pick?
 
To be safe you could start with a SS/DD Image and use that as a test. It will depend on your Floppy Drive's Heads. 1 Head is SS and 2 Heads DS.
The easiest way to know id remove the Floppy drive and look to see how many cables are connected to the two connectors for the heads.

While you have the drive(s) removed you can carefully clean the Heads with a Cotton Swab dipped in Alcohol. Gently rub any brownish deposits
until they are removed. I also clean the Guide Rods on Tandon TM-100 Series drives with a Cotton swab dipped in Alcohol. Then I lubricate them
with about three drops of Dri-Slide a Motorcycle Cable Lubricant. It doesn't attract dirt and lasts for years. Any Motorcycle shop should carry the
Dri-Slide. Then I gently move the head carriage assembly full travel in both directions. It makes the drive quiet and steps easier.


Larry
 
retrobecanes said:
Hi Durgadas311, I placed a check on pin 25 of the 1793 and I do get a pulse when I load a disk image in the emulator. When I "eject" the disk image, the pulse stops.
Most of the disk images that I find for 2.2G seem to indicate ROM 21-292A while mine just says 81-292. Is that okay?
Also I see some 2.2G images in SSDD and others in DSDD, which one should I pick?
Click to expand...

Given that you have a floppy emulator, probably best to get things working with that first and perform maintenance on the real floppy drives later. But, if there's any question about the emulator's fidelity, then other choices may be better. The native format for the Kaypro 2X/etc with 82-292 ROM is DD/DS, so that would be my suggestion to work with. Did you say you had original Kaypro floppies? Or are you only working with images generated on a modern PC? From what I hear, there can be complications creating images on a modern PC, having to do with getting the geometry specified correctly - not all images have a valid geometry encoded in them. Might be necessary to review that whole process.

I'm not sure what the difference is between 81-292 and 81-292a. The only image I've found online is 81-292a, and the 2X mainboard with 81-292 (not sure if it was "a") that I had went bad in 1986 and got replaced with the universal 81-478 series, so I have nothing to reference to.

The other possible hardware issue is the FDC 1793. But, you'd have to write some software to test that, and then figure out how to get that to run on a Kaypro that can't boot. Since the Kaypro ROM provides no commandline interface, debugger, etc, the only way I can think of is to write your own ROM monitor and replace the Kaypro ROM... not exactly a pleasant approach. I'm not sure if you can still get FDC 1793s anymore, so it may come down to scavenging other hardware.
 
durgadas311 , I do have original floppies that came with the 2/84 but at this point I have no way of knowing if those floppies are still any good. Yesterday I made a new DSDD floppy based on and .imd image of CPM 2.2G but it didn't work either. I have had a lot of luck with my Lotharek (HCX) SD floppy emulator on other systems but the KayPro doesn't seem to recognize it, so it could be that the .hfe images that I am using are bad or it could be that the 1793 is acting up and not accessing the Lotharek just like it is not accessing the physical drives. I have able to purchase a NOS FDC1793 that I should be received in a few days. I will see if replacing that part fixes the problem. At this point I see that as the next step. Now if the replacement of the FDC1793 doesn't fix the problem, what would be the next thing to try?
 
What is the Manufacture and part number of the Floppy Drives in your Kaypro? Are they full height or 1/2 Height? Have you
checked the Power Supply Voltages? You need 5.0 VDC and +12 VDC to power the Floppy Drives. If you have been
swapping drives around have you also set the correct Drive Select for DS{0..3}?

Since the Kaypro does not use a Floppy Cable with twisted conductors the drives need to be strapped for A: = DS0 and B: = DS1.
Only the last drive at the end of the Floppy Cable needs the Terminator resistor.

If all of this is correct I'd pull a drive and try it with another computer.

Larry
 
ldkraemer - see my comments below.
ldkraemer said:
What is the Manufacture and part number of the Floppy Drives in your Kaypro?

TEC FB-501

Are they full height or 1/2 Height?

1/2 Height

Have you checked the Power Supply Voltages? You need 5.0 VDC and +12 VDC to power the Floppy Drives.

Voltage @ drives are 5.1V and 11.72V.

If you have been swapping drives around have you also set the correct Drive Select for DS{0..3}?

Yes, as I was swapping the drives, I change the jumper settings and placed the terminator on B.

Since the Kaypro does not use a Floppy Cable with twisted conductors the drives need to be strapped for A: = DS0 and B: = DS1.
Only the last drive at the end of the Floppy Cable needs the Terminator resistor.

If all of this is correct I'd pull a drive and try it with another computer.

I have also tried with a Lotharek (HCX) SD Floppy Emulator, connected straight onto the motherboard but to no effect. That is why I think that the FDC1793 may be defective or some other chip on the board.

Larry
Click to expand...
 
You could remove the FDC U44 and then locate Pin 15 on the FDC IC Socket. If you pull that pin HIGH by using
a 1K PULLUP Resistor to +5VDC, similar to R45, the /STEP signal will go LOW at J8-20 (or U54 Pin 12, and
the Drive should step one step. Direction is set by Pin 16 being HIGH (Step IN) or LOW (Step OUT).
Probably the best thing to do is just add the 1K resistor from +5VDC to Pin 15 of the FDC IC Socket, then use
a jumper to ground (pull low) FDC Pin 15. That way you know you have a HIGH and LOW signal going to the
7406 Inverter.

Larry

Click image for larger version Name: k2-84FDC.png Views: 0 Size: 228.6 KB ID: 1216291
 
Last edited:
I have a TEC FB-504 that I bought sometime back but can't locate it at the moment, and I don't remember what I did with it.

Larry
 
Follow Pin 15 of FDC to Pin 13 of 7406 (U54), to Pin 12 of 7406 and on to J8-20. You should find the problem of J8-20 not
going LOW to give you a step* signal.


Larry
 
ldkraemer said:
Follow Pin 15 of FDC to Pin 13 of 7406 (U54), to Pin 12 of 7406 and on to J8-20. You should find the problem of J8-20 not
going LOW to give you a step* signal.


Larry
Click to expand...

ldkraemer provided that I am doing this correctly with my probe, I am reading 'low' on pin 15 of FDC, low on Pin 13 of 7406, nothing on pin 12 of 7406, and low on J8-20.
 
This doesn't seem possible. You need a HIGH on Pin 15 of the FDC to get a Low on J8-20. Double check that the RED stripe on the Data
Cable to the floppy's is on the Pin 2 side of the Edge connector of the Floppy Drive.

Larry
 
ldkraemer , you're right, I was not counting the J8 pins in the right order. So I have a low on pin 15 of the FDC and a low on pin 13 of the 7406. When I first turn on the computer pin 12 of the 7406 seems to be oscillating quickly (and so is pin 20 of J8) but then after a few seconds it stops and I don't get any reading whatsoever on either pin 12 of the 7408 or on pin 20 of J8.
 
OK, get yourself a 1.2K OHM resistor and solder a small diameter wire to one end of it. REMOVE the Z80 CPU and the 1793 FDC IC's,
making sure you know how they are oriented. The wire size needs to be small diameter so you do not destroy the IC Socket's
grip on the IC's pin's when the IC is re-inserted.

Locate Pin 21 of the FDC IC Socket, which is +5VDC. Insert the resistor's lead into the IC socket's Pin 21. Insert the small diameter
wire into Pin 15 of the FDC IC Socket. Turn on the Kaypro's power. Check for a HIGH (Greater than +2.7 VDC on Pin 15 of the
FDC Socket. Then follow that to Pin 13 of U54 (7406), then on Pin 12 of U54 (7406) where you should have a LOW (less than
+.7 VDC) on Pin 12 which will go to J8 Pin 20. If that checks out use another small diameter jumper wire from Pin 20 (GND) of
the FDC IC Socket, to the wire that is inserted into Pin 15 of the FDC IC Socket. The FDC Pin 15 should now be LOW (less than
+.7 VDC), and Pin 13 of U54 (7406) should be the same, but Pin 12 of U54 (7406) will be HIGH (greater than +2.7 VDC) and
so will J8 Pin 20.

Does this test locate your problem? if not unplug the data cable going to both Floppy Drives, at each floppy drive, and retest.

Larry


Click image for larger version Name: RS1793.png Views: 0 Size: 27.8 KB ID: 1217218
 
Last edited:
ldkraemer, when you say remove the Z80, is that the one in U43, to the left of the FDC? Asking since I notice two other Z80A processors in U11 and U17.
 
You must log in or register to reply here.
Back
Top