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PC 5150 Diskette Adapter

wrljet

wrljet

Experienced Member
Joined
Oct 31, 2008
Messages
351
Location
Maryland
I have the floppy controller from a 5150 I'm restoring, with the wide bracket.
P/N 1809113. It uses an Intel 8272 controller chip instead of the uPD765 found on my XT controllers,
along with some custom IBM "cans" that look like what they used in the 370 mainframes.

Does anybody have the schematic for this earlier board?
All I have is PC Tech Ref 2.02 and it shows the later board.

Pic below shows the PC board (top) vs. the XT board (bottom).

A larger version of the image is at:
http://www.wrljet.com/rennpics/PCXT-Diskette-Adapters.jpg

Thanks, Bill

PCXT-Diskette-Adapters-800.jpg
 
Since large parts of the PCB's are identical, I assume that the custom IBM chips are just the 5 TTL chips on the lower left (XT from the version) combined into some custom chips. As for scematics, I don't really think there are any huge differences except for that.
 
Wow, I never realized there were any differences in the diskette adapters, will need to dig through
my parts boxes and see which ones I have :)
 
If no one else has it, I have the schematics for the old one. The primary difference is in the data separator--the old uses some IBM hybrid circuits to form a PLL data separator; the new one uses some flip-flops and a MC4044 phase detector and a MC4024 VCO to accomplish the same. IMOHO, the old separator is by far the better one and the new one mostly a cost-reduction measure (it could be that IBM lacked the production capability for the hybrid devices in quantity). Later versions of the controller used a WD9216 data separator.

I replaced the 8272 on mine with a NEC uPD765AC. If you've got an 8272A, you're okay--they're basically the same. But the non-"A" 8272 has a very long (1 msec.) "blind spot" after index that can create problems with disks made on non-IBM systems.

Why do you need the schematic? You're not going fix the hybrid parts--there's almost no documentation on them. Mostly boxes with numbered pins.
 
I'm looking for the schematic because I'm trying to get a remote floppy running off the 37-pin connector
and things aren't what I'm expecting.

And I'd like to know what's on P3.

Bill
 
The DC37 has exactly the same pinout as the Rev. 2 one. Namely:
  • 1-5: NC
  • 6: Index
  • 7: Motor enable C
  • 8: Select D
  • 9: Select C
  • 10: Motor enable D
  • 11: Direction
  • 12: Step
  • 13: Head select
  • 14:Write gate
  • 15: Track 0
  • 16: Write protect
  • 17: Read data
  • 18: Write data
  • 19: NC
  • 20-37: Ground

Or, if you take a normal drive ribbon cable and crimp it into a DC37 IDC connector with position 34 of the ribbon cable in the pin 19 position of the DC37, you'll have it.

As far as P3, the 16MHz XCO is divided by 2 by section 1 of U2, 74LS109 JK FF. Pin 3 of P3 is connected to pin 5, PRESET* of the FF; pin 4 is connected to pin 1, CLEAR*. Both 3 and 4 are pulled high by 2 sections of RP2 (2K each). The idea is that you can drive pins 3 and 4 of P3 with an external clock and its complement for testing.
 
Thank you, Chuck, for the information. I now have the 4869 external drive jumpered to work on the 5150.

Do you recommend replacing that 8272 non-A?

Bill
 
You should have mentioned that you were working with a 4869--I've got a bunch of them here and have done the pair swap at the drive connector many times--so much so, that I have a method for using packing tape and working only by pair color to do it and re-use the original connector.

I do recommend replacing the original 8272 with either an "A" part or one of the NEC 765AC parts (or any one of the equivalents from other vendors). The 8272 was a bit buggy in addition to having some timing issues and the original diskette adapter was the only one to use it. And I'd recommend just installing a 40-pin socket, so that if you ever wanted to go back to the original, it would be very easy.
 
Chuck,

I didn't change the cable. I soldered a wire to the motor enable pin on the resistor pack, and wire wrapped that to the select jumper, and changed the select jumper from 1, to 0. One reason I wanted the schematic was to make sure nothing bad was going to happen.

It's working well.

Pic:
http://www.wrljet.com/rennpics/4869-mod.jpg

Bill
 
I wanted something that would work with any drive; even a 3.5-5.25 dual drive, so reworking the connector was most expedient for me. If I jumpered the drive, then I'd have to remember that the next time I swapped a drive in the box.
 
finding this thread, i am going to ask, i have one of those 4869s and it refuses to work, i replaced the ALPS drive with a mitsumi one as the ALPS failed, but the mitsumi refuses to work on my 5160's or my 5150. I'd like to be able to slap a 720kb in this sucker and be able to use it with my 5150. Is this even possible? or do i need to do that little jumper trick?
 
k2x4b524[ said:
finding this thread, i am going to ask, i have one of those 4869s and it refuses to work, i replaced the ALPS drive with a mitsumi one as the ALPS failed, but the mitsumi refuses to work on my 5160's or my 5150. I'd like to be able to slap a 720kb in this sucker and be able to use it with my 5150. Is this even possible? or do i need to do that little jumper trick?
Click to expand...

You can either jumper your drive or swap a couple of conductors at the connector. I like to pry off the connector, pull off the wires that need swapping, then re-assemble the connector (it helps if you have an IDC crimper). It looks exactly like the original; the difference is that the wires now correspond to the 5150 ordering. You could also cut and splice the leads going to the connector. ISTR that it's only a couple of wires that need swapping to work for both drive/motor selects.

If you'd prefer, I can post the Diskettte Adapter/A pinout and you can compare it with the 5150 pinout shown above.
 
k2x4b524[ said:
by jumpering the drive, you mean setting the drive select? Pardon my stupidness, but i had assumed that the external box did this for you, or does the drive jumper HAVE to be like DS1,2,3,4 or which ever?
Click to expand...

The ALPS DFC222B05A drive in mine is not capable of being jumpered to work with the options provided natively. I had to add a wire for the MOTOR signal in addition to strapping DS0. (as shown in the pic I linked)
 
Okay, here's the DAA connector pinout:

  • 1: NC 2: High Density
  • 3-5: NC
  • 6: Index
  • 7: Reserved
  • 8: Select C
  • 9: Reserved
  • 10: Motor enable C
  • 11: Direction
  • 12: Step
  • 13: Head select
  • 14:Write gate
  • 15: Track 0
  • 16: Write protect
  • 17: Read data
  • 18: Write data
  • 19: Diskette changed
  • 24: Drive C installed
  • 20-23, 25-37: Ground

The important thing to notice is that the select on a 4869 is reversed--the drive C select and motor enable are where the drive D ones normally would be. It takes a little playing around--nothing major.
 
Chuck(G) said:
You should have mentioned that you were working with a 4869--I've got a bunch of them here and have done the pair swap at the drive connector many times--so much so, that I have a method for using packing tape and working only by pair color to do it and re-use the original connector.

I do recommend replacing the original 8272 with either an "A" part or one of the NEC 765AC parts (or any one of the equivalents from other vendors). The 8272 was a bit buggy in addition to having some timing issues and the original diskette adapter was the only one to use it. And I'd recommend just installing a 40-pin socket, so that if you ever wanted to go back to the original, it would be very easy.
Click to expand...

Your recommendation to check the 4869 cabling is a good one, because the PS/2 adapters these units were designed to work with did truncate certain drive-select lines. A microchannel adapter with a FDC even had a somewhat-standard 34-pin connection that was only designed to run one internal drive. Without the stuff immediately at hand, I don´t remember what the drive has to be set.

EDIT: Whoops, just saw you addressed this...
 
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