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Resurrecting a IBM 5150: 601 code at POST. Need some help.

madmaxamdam

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Oct 25, 2012
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I am trying to resurrect and old 5150 that was given to me as "not turned on in decades".
It's a 1984 rev3 bios, with 256k RAM on board and 256k RAM on expansion card.
It comes with two 5.25" floppy drives, monochrome monitor and keyboard, all pieces belonging to the original setup from IBM.

Not feeling confident in turning it on in an unknown status, I have disassembled it, thoroughly cleaned it from years' dust and dirt, then I started testing by adding the now shiny pieces one by one:

1. Minimum Diagnostic Configuration Test - PASSED (one long and two short beeps as expected)

2. Adding Video Adapter Card and Monitor - PASSED (POST positive with no error codes, BASIC command prompt as expected - this has been a touching moment!)

3. Adding Keyboard and testing all keys - PASSED

4. Adding the 256k RAM expansion - PASSED (POST positive - well... the second time through, after a first failing attempt where I realised I did the DIP switch configuration *cough*wrong*cough*. Damn'd ON=0 / OFF=1 rule :rolleyes:)

And now, on to the floppy drives...

5. Testing the voltage of both power connectors to the floppy drives (with drives detached) - PASSED (+5V and +12V as expected)

6. Adding the floppy disk controller card, and ONE floppy drive as drive A: - FAILED (POST 601 code, and no reaction from the drive: no red light, no noise)

7. Removing the first drive and adding THE OTHER ONE as drive A: - FAILED (same as above)

8. Trying with BOTH drives - FAILED (same as above)

At this point I'm a bit stuck.

Given the above tests, I tend to believe that the the issue might be on the controller card (chance that drives are BOTH dead should be lower...).
But I was not able to find much documentation on the floppy controller card.

Any ideas on how to proceed further and nail down the issue?

Thanks in advance!
Cheers,
Max
 

vwestlife

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Try cleaning the contacts on the card edge connectors of the drives and controller. Since the computer has been sitting for a long time they could be oxidized.

Note that the early PC floppy drives were not directly swappable between A: and B:. The A: drive will have the resistor termination pack installed while the B: drive will not. So if you want to exchange the drives you have to move the resistor pack to whichever one the A: drive will be. With the full-height drives, it's towards the rear of the circuit board and looks like an IC but is tan or blue colored.

Both drives should be jumpered to the second drive select setting (DS1 if the jumpers go DS0 to DS3, or DS2 if the jumpers go from DS1 to DS4), and the A: drive goes on the end of the cable, after the twist.
 

Old Computers

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Max,

I believe that you are correct that the FDD card causes the error. I have a Compaq Portable that has issues with the FDD controler. 601 appears on the screen when I boot it (or at least what looks like that, the display is not functioning properly). There are no beeps from the computer, but I did change the card with another one and the FDD appeared to work properly. If I remember correctly the 601 did not appear after that.

If you have a newer old computer (90's-early 00's) with a FDD controller, you can set the BIOS to recognize a 5 1/4" drive. You might need the right kind of cable though. Connecting the drives to that computer will test to see if the drives themselves are functioning.

Old Computers
 

RJBJR

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453
Two quick and simple things.
Try the card in a different slot.
Try a different floppy ribbon cable.
 

Stone

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Along with the above suggestions, are the switches on block 1 switches 7 and 8 set correctly for each configuration you are trying?


  • Switch 7,8
  • ON,ON = 1 floppy drive
  • off,ON = 2 flops
  • ON,off = 3 flops
  • off,off = 4 flops
 

madmaxamdam

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Thank you guys for your suggestions, I'll try them out in a few hours as I get back home and keep you posted.

I did set block 1 switches as described by Stone, but I'll double/triple check again when running the new tests.

@RJBJR: I'm a bit ashamed I didn't already try very simple things like different slot/different cable (I agree with you: have to be paranoid when testing, and think about ALL possible points of failure).

@vwestlife: about the resistor termination pack, I noticed the blue chip it but failed to recognize its purpose. I'll now make sure it always sits on drive A:

One last question to vwestlife: I do not have the drive boards in front of me right now, but I remember there was a black chip slot that had a metallic wire shorting two opposite pin holes.
Is that the one I should look at for drive jumping? If so, will I find reference to the DS1/DS4 pin holes printed on the board?
 

vwestlife

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One last question to vwestlife: I do not have the drive boards in front of me right now, but I remember there was a black chip slot that had a metallic wire shorting two opposite pin holes.
Is that the one I should look at for drive jumping? If so, will I find reference to the DS1/DS4 pin holes printed on the board?

The full-height IBM floppy drive in my 5150 PC has that same metal jumper in an IC socket, and I do believe that is the drive select jumper, but I'm not 100% sure. Generally with the original IBM drives you never have to worry about the drive select jumpers, but if you're using an aftermarket drive from an unknown source, you do have to pay attention to that, because the drive might have come from some other computer brand (like Tandy) which used DS0 for A: and DS1 for B: instead of setting both to DS1 and using the twist in the cable like IBM did.
 

Stone

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6. Adding the floppy disk controller card, and ONE floppy drive as drive A: - FAILED (POST 601 code, and no reaction from the drive: no red light, no noise)

7. Removing the first drive and adding THE OTHER ONE as drive A: - FAILED (same as above)
Based on these two tests it seems that either the controller or the ribbon is the source of the problem. I'm inclined to go along with your assessment that's it's the controller. You should be able to test the controller in any machine with an ISA slot, either 8-bit or 16-bit. But, trying another ribbon wouldn't hurt either. :) Neither would trying another floppy controller in the 5150.
 

madmaxamdam

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Status update.

Tested again, with one floppy drive at a time:
- using a different slot for the controller (the one that previously hosted the video adapter, which proved to be working)
- being 100% sure that switches 7,8 of bank 1 are ON,ON (=1 FD)
- having the drive always connected as A: (at the far end of the cable, near the twist)
- moving that resistor termination chip so that it was always sitting on the connected drive
- leaving the jumpers in the drives just as they are (after all, those are two original full-height IBM drives, the jumpers are exactly in the same position on both, and firmly attached to their IC sockets. I'm pretty sure none touched them before.)

The result is always the same: 601 for both drives.

Now next step would be opening that non-working IBM XT I have in my stock waiting for its turn, in order to borrow the ribbon and the controller, and substituting them one by one, as per Stone suggestion.

I will report the results later.

Unfortunately I can't test on another machine the current 5150 controller nor the drives (as per Old Computer suggestion) because the XT does not even power on, and other newer old computer is not currently in my reach.
 

madmaxamdam

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Changing the controller (i.e. using the one from the XT) finally gave the result: clean boot with no POST codes and drive reacting at check time!
Tested with both drives, and both ribbons, and they are all good. So the issue definitely lies within the PC floppy controller board!

Now, the problem is that I have two machines (the PC and the XT) and only one working floppy controller. :(

I found some documentation on the controller and started reading it, and see what I can do.
From your experience, is it worth spending some time trying to figure out what's wrong with the controller (e.g. how difficult would be to find an adequate equivalent if I find out the problem is a bad IC)?

Any suggestion on frequent failure causes, and/or what tests should I perform first?

Thanks in advance for your help!!

*gets back to reading*
 

vwestlife

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Something simple to check: the original IBM PC/XT floppy controller has one jumper on it. I forget whether the jumper is supposed to be installed or not (I haven't had one in years), but either way, if you don't have that jumper in the correct position, the controller may not work. Hopefully someone can chime in with the correct answer -- I tried searching, but couldn't come up with anything specific about it.
 

Stone

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Something simple to check: the original IBM PC/XT floppy controller has one jumper on it. I forget whether the jumper is supposed to be installed or not (I haven't had one in years), but either way, if you don't have that jumper in the correct position, the controller may not work. Hopefully someone can chime in with the correct answer -- I tried searching, but couldn't come up with anything specific about it.
That jumper, P3, enables/disables the controller. Closed = enabled; open = disabled. I just tried it on my XT with that card.
 

madmaxamdam

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Found!
The jumper is there.
It's named P3 and it's near the back end of the board (next to the cable connector).

Guess what? On the working controller the jumper is shorted, while on the original (faulty) one it's open!

I'm going to close that jumper and test again the original board.
Holding my breath until next post...
 

madmaxamdam

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Closing the jumper "fixes" the controller. Now the PC is fully functional again!
Thanks for all your help!

@Chuck:
The controller I found in the PC actually looks very similar to the one in the XT: chip vendors and part numbers are different, but the PCB layout and components are exactly the same (see pic below - PC controller is on top).
Please consider my PC is a 1984 version, not an "original" from 1981. May be IBM mounted a newer version of the controller on later PCs?

FDD_Controllers.jpg
 

madmaxamdam

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A little gift for you guys, for all the help you gave me.

THE RESURRECTED IBM PC IN ALL ITS GLORY

5150 Ok.JPG

(in the backgroud, my multimeter and the bottle of alchool used for cleaning the old lady)

Cheers,
Max
 

Chuck(G)

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Well, that's not the "original" 5150 floppy controller. The original one has a number of metal-can IBM hybrid circuits on it. The one you have is a later version of the controller.
 
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