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5150 Post Code 601

Chuck(G) said:
The reason I ask about the BIOS is that the 5160 calls SW1 "unused" and the XT documentation seems to imply that you must have a floppy controller installed.
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I haven't looked, but would someone put a 5160 BIOS ROM in a 5150 system board? I guess if that is the case, it makes sense, but if not and it is still a 5150 BIOS ROM in this thing, what's making it go nuts?
 
patscc said:
Do you have a VGA you can slap in there instead of the mono card ?
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What would that do that the mono doesn't?

FWIW, I have used lots of 16-bit VGA cards in my XT with no problem. They were mostly Trident and Cirrus cards. There was the occasional 16-bit card that wouldn't work, however. Sorry, but I can't enumerate which ones did work OK and whick didn't. :)
 
You can have it at a different address in memory than MDA. Note I didn't say it would fix anything, just something to try until someone comes along with a 5150 handy that they can play around with and see if they can replicate the condition.
patscc
 
lyonadmiral said:
It fails the test... Switch 1/1 I suspect is what the problem is, so with that in mind, what's next, can this even be fixed?
Click to expand...

Maybe--if it is indeed bad. Pull the motherboard out of the box, flip it over and check SW1 operation with a continuity tester. Or, if you have the diagnostic ROM that we've been chattering about on another thread, see what it says about the switch. You can also use the built-in BASIC to show the switch setting, if you can get to it.
 
Compressed air ? If there's a Rat Shack near you, they should have some contact cleaner ( also called tuner cleaner ), or possibly at a car parts store.
patscc
 
lyonadmiral said:
It fails the test... Switch 1/1 I suspect is what the problem is, so with that in mind, what's next, can this even be fixed?
Click to expand...
The SW1 circuitry is shown on page 1-45 of the document [here].
There is a drawing error - pins 1 and 19 of U23 are not connected to pin 13.

The 5150 uses port A on the 8255 chip for both keyboard and SW1.

Because your 5150 is reading keystrokes fine, that means that the cause of the SW1 problem is limited to:
1. SW1 itself
2. RN2 (resistor network)(unlikely)
3. Chip U23
4. Bad solder joint.

If you had a multimeter, then we could instruct you on how to narrow down the cause.
 
An Interesting Development

An Interesting Development

So I changed the configuration, set the switches for 1 floppy and installed a controller and a drive. I still get Error 601, I swapped out for a spare controller and a spare drive, still get 601. What is the possibility of having two dead controllers and drives?
 
lyonadmiral said:
So I changed the configuration, set the switches for 1 floppy and installed a controller and a drive. I still get Error 601, I swapped out for a spare controller and a spare drive, still get 601. What is the possibility of having two dead controllers and drives?
Click to expand...


Not very likely. Can you boot from hard disk?
 
Can you get your hands on either a multimeter, or a logic probe ? I think you're at the point where you need to start tracing at pin 7 of U23 ( LS244 ) to see if maybe it's a bad chip.
patscc
 
Guys, I need an opinion. If lyonadmiral manually pulls the pin 7 on U23 (the output of the gate buffering SW-1) high, would that screw anything up ? In theory, this should let the PPI read the correct value during boot.
patscc
 
I think the problems run deeper than that. Even when he inserts a floppy controller, he gets a 601. I'll take a peek at the BIOS code when I get a chance to see what produces it.
 
Well, let's see here. A 601 error can come from the FDC failing a simple reset (when reset is released, the FDC should issue an interrupt), or fail a seek to cylinder 1 or 34. Note that in no case is DMA involved in the test. So a dead 8259 could result in a flop. The BIOS code also verifies that bit 0 on the equipment status port is queried for diskette support. Note that only drive 0 is tested.

@LA: when you had the FDC and drive hooked up, did the drive ever get selected (LED on) or seek (you should hear that)?

So my suspects are (1) the 8255 (2) a flakey memory chip that's not getting caught (3) power supply issue.

@LA: Does the thing ever get to BASIC?
 
Chuck(G) said:
The BIOS code also verifies that bit 0 on the equipment status port is queried for diskette support.
Click to expand...
Which is set/reset per switch 1 on SW1.
If switch 1 on SW1 is ON, the 601 test is skipped.

Chuck(G) said:
@LA: Does the thing ever get to BASIC?
Click to expand...
I'm pretty sure he is going to come back in the affirmative - he did my BASIC test of SW1 at post #26.
 
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