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IBM PC 5150 stubborn POST 601 error

P

philippe_d

Member
Joined
Jun 26, 2019
Messages
29
Location
Belgium
Hello guys,

My name is Philippe and I am trying to get an IBM 5150 to work.
The machine is a 2nd revision of the motherboard and has the 3rd revision of the bios.
The machine powers on and shows the 601 POST error (floppy error) then it loads basic and basically the PC works great in basic but i'd like it to be more useful than just basic :)

What I did so far:
1. I checked the switches on the motherboard to check that the correct number of drives was selected. (switches ok)
2. I checked the cable to the floppy drives, the correct connector connected to the correct drive and the terminator dip package on the last drive on the cable. (so cable connections ok)
3. I swapped the controller card. (no success)
4. I tested both disk drives in a 386 and they work perfect on the 386, I was able to read and write to the floppy drives. (so drives are ok)
5. I used the power cables of the IBM PC but left the floppy drives data cables connected to the 386 -> they still work work fine (so power is ok)
6. I acquired an XT clone and I replaced the controller card with the controller card and data cable of my IBM PC and the disk drives work fine in the XT clone (Meaning that the controller and cable are also ok)
7. I tried to place the controller card in every single ISA slot the PC has. ( no success)
8. I tested with only 1 drive and changed the switches on the motherboard to indicate I only have 1 drive and tested this with both drives putting the terminator dip package on the drive that was connected but no success.
9. I tried with floppy drives from the XT computer but no success.

so as a summary:
floppy drives tested and ok
power tested and ok
data cable tested and ok
controller card tested and ok
terminator checked and ok
motherboard switches checked and ok
ISA slots seem to be ok (They work for my VGA and MDA card)

-> still 601 error in my IBM 5150

I'm completely out of ideas now.. I hope someone here has seen this before and can give me a clue where to look next.
 
1. On an IBM 5150, about 50 seconds or so after power-on, expected to be observed is the A: drive's disk access LED turn on momentarily, the drive's spindle turn, and the drive's heads moving out to track 34. Seeing any/all of those ?

2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)
 
modem7 said:
1. On an IBM 5150, about 50 seconds or so after power-on, expected to be observed is the A: drive's disk access LED turn on momentarily, the drive's spindle turn, and the drive's heads moving out to track 34. Seeing any/all of those ?
Click to expand...

With the controller card in the 5150 no
With the controller card and floppy drives an XT clone yes.

modem7 said:
2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)
Click to expand...
I didn't check with a multimeter but I thought I ruled that out by powering the floppy drives from the 5150's power supply while having the data cable connected to my 386. (and that worked I could use the drives in the 386 while powered from the 5150 PSU.)
I believe I even did the test the other way around too. powering the drives from the 386 and the data cables to the 5150. (with the same 601 error as a result but it's been some time since I tested this so it can be my imagination)
So I was quiet sure back than it had to be the controller card. (so I bought a spare one online which was promised to be working, but I got the same error with the spare card)
Only last weekend I found an XT clone and thought that was perfect to test the controller card. I was annoyed to found out that the controller card worked in the XT clone.... so that rules out that the controller card has an issue I believe.
Anyway I will take your advise and measure with a multimeter just to be sure.
 
The floppy controller relies on two devices for successful operation--the 8259 interrupt controller (IRQ 6) and the 8237 DMA (DMA channel 2) controller. It could well be possible that there's a discontinuity or fault between the ISA bus and either of these devices. An oscilloscope or logic analyzer might pick up the problem.

It's also possible that the address decoding for the ISA bus isn't working. That can be checked from BASIC.
 
philippe_d said:
Anyway I will take your advise and measure with a multimeter just to be sure.
Click to expand...
Yes, just to be sure.

In addition to what Chuck wrote, you could try a Supersoft/Landmark diagnostic ROM (via adapter) in motherboard socket U33.
It may show a motherboard problem, pointing out the problem area.
 
Under BASIC, try the following:

Code: 
OUT &H3F2,&H1D

The LED on drive A: should go on and the motor should start spinning.

Code: 
PRINT INP(&H3F4)

You should get 128. This will at least verify that your card is seen by the system.
 
Thanks guys these are very useful replies.

I'll measure the voltage on the floppy drives for +12v and I'll try the basic commands from Chuck to verify if the controller card can be seen by the system.
I don't have an oscilloscope so I hope I'll not need one of those..
That diagnostics rom will also need to wait for now, I don't have one so I'll need to get me an eprom programmer or I see there are some people that can program one for me: http://www.minuszerodegrees.net/rom/misc/eprom_programming_services.htm
 
The really early IBM floppy controller with tin cans also use -5V if I am not mistaken. That's also something to check.

You might also try a general purpose Floppy-controller in the XT. Doesn't matter if it's on a multifunction card that's 16-bit, as most later FDC chipsets only use the 8-bit portion of the ISA bus.
 
Chuck(G) said:
Under BASIC, try the following:

Code: 
OUT &H3F2,&H1D

The LED on drive A: should go on and the motor should start spinning.
Click to expand...

No success... not a single sign of life...

Chuck(G) said:
Code: 
PRINT INP(&H3F4)

You should get 128. This will at least verify that your card is seen by the system.
Click to expand...

No success... I get 0 back

modem7 said:
2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)
Click to expand...

I measure +12.11V on the output of the PSY going into the drives. (and 5.12V on the other wire)
 
per said:
You might also try a general purpose Floppy-controller in the XT. Doesn't matter if it's on a multifunction card that's 16-bit, as most later FDC chipsets only use the 8-bit portion of the ISA bus.
Click to expand...
I have tried the XT controller in the 5150 but also this controller doesn't work in the 5150. no spin no leds turning on, just the 601 error....
 
Chuck(G) said:
The floppy controller relies on two devices for successful operation--the 8259 interrupt controller (IRQ 6) and the 8237 DMA (DMA channel 2) controller. It could well be possible that there's a discontinuity or fault between the ISA bus and either of these devices. An oscilloscope or logic analyzer might pick up the problem.

It's also possible that the address decoding for the ISA bus isn't working. That can be checked from BASIC.
Click to expand...

I just used my multimeter to check the continuity between the ISA bus and the 8259 on IRQ6. continuity for the IRQ 6 channel is ok.
For the DMA, I located the 8237 but I'm not sure which pin to follow where...
 
I've been doing some extra testing.
1. I installed controller and floppies in the XT and everything works fine in the XT
2. I installed the PSU of the XT in the 5150 and moved the controller and floppies back to the 5150 as well -> result same 601 error, no spin not a single trace of life in the floppy drives.

So I'm sure controller, floppy drives and PSU are ok(because they all work in the XT). The problem has to be on the main board of the 5150 but it only seems to have an impact on the floppy controller and not on the video card or anything else I know off.
IRQ6 trace checked on continuity from the ISA bus to the 8259 interrupt controller and that trace is also ok.
what can I check next? Is it time to go searching for an eprom programmer and make those diagnostic roms?
 
Have you checked sw1:7/8 for continuity? Test with meter on underside of board to see if switch contacts are actually contacting. I have a board with this problem on sw1:5, and it does not make contact when the switch is on, so the motherboard gives display beep error when set for CGA because SW5 actually remains off even when appears to be switched on. I wonder if you perhaps have a bad Switch 7 or 8 that the floppy config might not actually be set as appears.
 
chris_nh said:
Have you checked sw1:7/8 for continuity? Test with meter on underside of board to see if switch contacts are actually contacting. I have a board with this problem on sw1:5, and it does not make contact when the switch is on, so the motherboard gives display beep error when set for CGA because SW5 actually remains off even when appears to be switched on. I wonder if you perhaps have a bad Switch 7 or 8 that the floppy config might not actually be set as appears.
Click to expand...

No, I haven't checked that yet but that is a good point. I'll do that thanks.

I checked the -5 volt pin on the ISA slot as well now. It measures -4.7V Could this be too low or is it still within specs?

regards,

Philippe
 
Chuck(G) said:
Under BASIC, try the following:
Click to expand...
Looking at the behaviour of my two functional IBM 5150's:

Chuck(G) said:
PRINT INP(&H3F4)
You should get 128. This will at least verify that your card is seen by the system.
Click to expand...
On both my 5150's, 16 was seen !!!
Then I discovered that if I powered up the 5150's with its floppy drive disconnected from the controller, then I saw 128.

If I removed the floppy controller from the 5150's, returned, as expected, was a large number, 255 in one case and 233 in the another.

Chuck(G) said:
OUT &H3F2,&H1D
The LED on drive A: should go on and the motor should start spinning.
Click to expand...
That did not work. I then discovered from [here] that the &H1D should instead be &H1C
 
Phillipe--you need to clear your messages out. Apparently your inbox is full.

Yes, that should be &H1C for the first drive and &H2D for the second.
 
Reading through this thread you never said what type of floppy drives you have- are they just a matched pair of standard IBM 360KB full height drives or are you mixing drive
types/sizes/densities?

Mike
 
philippe_d said:
I checked the -5 volt pin on the ISA slot as well now. It measures -4.7V Could this be too low or is it still within specs?
Click to expand...

Should be fine ... I think the spec for TTL logic is 2.7-5v for logic 1 and CMOS is 3.5v-5v for logic 1. I think the 5v spec is also +- .25v, so 4.75v should be completely acceptable.
 
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