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IBM PC 5150 displays 601 on boot

everything connected and switches set to "do not boot from floppy drive" = no error, machine boots in Basic
both drives disconnected and switches set to "do not boot from floppy drive" = no error, machine boots in Basic
entire controller disconnected and switches set to "do not boot from floppy drive" = no error, machine boots in Basic

MikeS said:
I'm still curious what error (if any) one should get with the switch set for floppy drive(s) but no drives connected, and with the controller completely removed for that matter, and if that's what you get.
Click to expand...

switches set to normal (boot from floppy drive, 2 drives), both drives disconnected = error 601
switches set to normal (boot from floppy drive, 2 drives), entire controller disconnected = error 601

Does this mean that the error occurs on the motherboard? Or maybe the power unit?
 
5150 said:
switches set to normal (boot from floppy drive, 2 drives), both drives disconnected = error 601
switches set to normal (boot from floppy drive, 2 drives), entire controller disconnected = error 601
Click to expand...
Normal.
On my 5150, with one floppy drive and motherboard switch SW1-1 off, I see a 601 error in the following situations:
* Controller removed.
* Controller fitted, but cable between controller and drive removed.
* Drive fitted to wrong connector on cable.
* Drive Select jumper on drive in wrong position.
 
Looking at the source code for the 5150 BIOS (third revision), the code in the POST for the 601 test is performing:

Step 1: Get BIOS to perform a 'reset'.
- BIOS issues a 'reset' command to controller
- If failure indicated, abort after displaying 601 error

Step 2: Activate spindle motor via direct command to controller (same command also enables DMA/INT on controller).

Step 3: Wait 1 second

Step 4: Move heads to track 1 (via call to SEEK subroutine in BIOS)
- If failure indicated, abort after display of 601 error and deactivation of spindle motor

Step 5: Move heads to track 34 (via call to SEEK subroutine in BIOS)
- If failure indicated, abort after display of 601 error and deactivation of spindle motor

Step 6: Deactivate spindle motor

On your drive, you are seeing the access light come on, the spindle turn, but no head movement.
So that means that the POST has successfully commanded the controller to 'reset' and then to activate the spindle motor (via separate commands).
Step 4 or 5 is failing.

As expected, I was able to achieve the same thing (access light on / spindle turning / NO head movement / 601 error) by disabling the drive's stepper motor (by disconnecting P12 at rear of drive).
 
A problem we see periodically in old computers is poor electrical contact (having deteriated over time).

If you haven't done it already, try reseating (a few times) the cable connector that fits onto the floppy controller. That should fix possible poor contacts there (e.g. DIRECTION / STEP / TRK0).

If you haven't done it already, try reseating the floppy controller a few times. Because of post #21, I know you have done it at least once. And try a different slot.
 
modem7 said:
On your drive, you are seeing the access light come on, the spindle turn, but no head movement.
So that means that the POST has successfully commanded the controller to 'reset' and then to activate the spindle motor (via separate commands).
Step 4 or 5 is failing.
Click to expand...

Yes this is exactly what happens.

I have reseated the floppy controller quite a few times now.
Just tried a different slot -> no luck.

One more thing:
Two weeks ago I put power to the machine for the first time in 20 years.
The result was: no display, spindle motor and red light of floppy drive didn't work, I did hear the fan spinning.
During second boot I smelt something burning (at the time I thought it was dust).
On third boot the screen came on and the light of the floppy drive come on faintly.
It was like the floppy drive didn't get enough power to start.
I then heard I small explosion coming from somewhere inside the computer (not the screen).
On the next boot the display, spindle motor and red light came on.
On visual inspection I saw no burns or blacks. Everything looked as it should be -> clean and almost no dust inside.
I now think that I might have lost a vital component in the power unit used to provide power to the stepper motor.

Is there such a component that might have been damaged after all those years?
Could the problem be inside the power unit?
Can the lid of the power unit come off for inspection?
 
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I took the power unit out, looked inside -> nothing unusual.
There are 2 sets of 4 wires going from the power unit to the floppy drives, yellow, blue, black and red.
And from there, there are 4 different wires in each drive (connector 12) going to the stepper motor: white, green, red and black.
With both my stepper motors malfunctioning I guess I should be looking at the power unit feeding both drives.
Which of the wires is doing what?

It's either this or the controller since both stepper motors malfunction.

Is there any other component that controls both stepper motors?
 
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Take a meter and check the voltage. But since the mainboard works and so does the fan in the power supply as well as the spindle motor(s) in the drives that indicates that both 12V and 5V are present.

This is the last time I will say this. You need to verify the integrity of the floppy controller assembly. That includes the ribbon cable.
 
You might be right Stone but I have only 1 controller card and no other assembly to test with.
I would therefor like to rule out all other possibilities.
Is there a way to test the card / capacitors without the aid of another computer?
Which part of the card is controlling the stepper motors?
The machine has a lot of sentimental value to me.
I prefer to fix the card over buying a new one.
 
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For the stepper motor in the drive to move the head assembly, there are three requirements:

1. Head assembly in drive is free to move. You have made sure that it is, in both drives.
2. Floppy drive (good) is receiving the required commands/signals from the controller.
3. Floppy drive (good) is receiving +5V and +12V from power supply.

Regarding point 1.

Besides the deteriorated lubrication, I can not think of anything else that would have deteriorated in both drives that would result in the symptom (that is, same symptom in both drives). At this point, the probability is very high that both drives are good.

Regarding point 2.

That is why I suggested the connector reseating and why others are suggesting a check of the ribbon cable. I know that you said that the computer was working many years ago, but maybe then there was a latent fault in the cable.

Regarding point 3.

In post #26, your "One more thing:" text highly suggests to me that a tantalum capacitor initially went partially short circuit and then 'blew' itself open circuit (the "explosion"). I am sure that it you look hard enough, you will eventually find a damaged tantalum capacitor somewhere. Example photos are at http://www.minuszerodegrees.net/failure.htm

However, maybe such a damaged tantalum capacitor is still affecting the power supply, resulting in the +12V being significantly lower than it should. For example, +10V might be enough to turn the power supply fan and turn the drive spindle, but not enough for the stepper circuitry in the drive.

In theory, if your power supply is the original IBM 63W one, then the power supply won't allow the motherboard to start if the +12V is below specification.

In any case, per Stone's suggestion, you really need to measure the +5V line (red wire) and +12V line (yellow wire) at the plug that attaches to the floppy drive, to verify that they are at the correct level.
 
Thanks for all the help.

- Yesterday I placed an ad for a 'new' controller card. So far I had no reactions, I'll have to be patient.
- Today i'll check the ribbon cable, measure the +5V and +12V lines and look for faulty tantalum capacitors. On previous inspections I couldn't find any black or exploded ones.

@modem7
This page http://www.minuszerodegrees.net/failure.htm describes precisely what happened.
Visually I couldn't find any faulty capacitors though.
I'll have another look for tiny black spots.
What worries me is the sentance below the picture: "Do not assume that because a tantalum capacitor shows no damage, that it is good. Faulty tantalum capacitors often show no visible indication of failure".
I'm still thinking the problem might be in the power supply unit because of the burning odor after the explosion. explosion -> fan -> burning smell
Am I correct to say when the +5V and +12V lines are ok the capacitors should be ok and consequently the power supply is ok too, in which case I wouldn't have to worry about whatever happend during the explosion because no damage was done?
 
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5150 said:
I'm still thinking the problem might be in the power supply unit because of the burning odor after the explosion. explosion -> fan -> burning smell
Click to expand...
The air flow is from within the computer case into the power supply (via fan) and then is pushed out of the computer through the external vents of the power supply.
Therefore, an odour in the case will also appear in the air being vented out of the power supply.

5150 said:
Am I correct to say when the +5V and +12V lines are ok the capacitors should be ok
Click to expand...
No. If a faulty capacitor has failed in such as a way as to 'blown' open circuit, then it is if the capacitor is not there.
It will not be overloading the power supply, but because the capacitor is not providing any capacitance, you could not consider the capacitor to be okay.
 
5150 said:
What worries me is the sentance below the picture: "Do not assume that because a tantalum capacitor shows no damage, that it is good. Faulty tantalum capacitors often show no visible indication of failure".
Click to expand...

You heard an "explosion", together with an odour. That suggests that a component has failed somewhere and that there should be visible evidence of the failure. The component that has failed might not be a capacitor, however, a failing tantalum capacitor fits extremely well with the symptoms you wrote of in post #26, and failing tantalum capacitors is a common problem in the IBM 5150/5155/5160 (particularly ones that have been powered off for many years, like yours).

Often, people will write that their 5150/5155/5160 was never turning on. A visual inspection did not reveal anything. But eventually, a flick of the power switch resulted in a 'bang' sound, and then their 5150/5155/5160 turned on. That is typically a tantalum capacitor. Initially the capacitor had gone short circuit, always overloading the power supply, stopping the computer from starting. But on one subsequent application of voltage, the capacitor has 'blown' open circuit.

Sometimes a faulty component that has visible indication of failure can't be readily identified as such. I have fault-found boards down to chip level and when I desoldered a chip that I deduced to be faulty, sometimes there would be a crack on the underside of the chip.

But when you get your computer going, if you have not at that time found the source of the "explosion", then I don't think you should worry about that.
 
I am presuming that you have checked the ribbon cable and voltages (per your statement in post #33) and found nothing wrong with them.
 
Today I made someone an offer: 35 euro for a floppy controller including the ribbon cable.

Can't test with a 1,44M drive because I don't have any other floppy drives lying around.
I prefer to restore the computer to its original state.

I hope the guy sells me the controller card and then I hope and pray that it works :D
 
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