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Need help with my old IBM XT 5160

It should be possible, if you got some digital-cirquicy experience, to make a device that read bytes sendt out from the Keyboard port. Checkpoint bytes are sendt out of the keyboard port if the system get past the essencial MoBo tests (processor, DMA, ect...). If any bytes are sendt out, you would know that the MoBo starts, and be able to find out on what test it fails.

However, only internal testers at IBM in the 80's had sutch equipment, so I really don't know if you would be able to make one. You problably need some kind of a shift register, but that's as far as I know.

If it is that the MoBo is faulty, you could replace the BIOS with a custom BIOS designed for repairing. you would problably need a bus examining card in addition to this. I haven't tried to repair a motherboard bfore, but I know some other peoples here have experience with it.
 
If you're not getting any beep/error codes, and you might want to check that the speaker is connected to the motherboard (I have no idea how to determine if a speaker is good), you're at the reseating chips stage, though modem may have other ideas too so I'd keep my eye on the list a bit longer too. Reseating the chips that you can, can fix any minor issues like oxidation on the leads and also possibly point out a bent pin. Always worth while to do though.
 
modem7 said:
With no video card in a 5160, a beep (actually three beeps of long-short-short) is only expected if the motherboard switches are set to monochrome or CGA.
If motherboard switches are set to EGA, there will be no beeps (beeps generated due to no video card).
Click to expand...

I'm assuming that the OP has done his homework on switch settings. He could also pull a DRAM chip out of its socket to force an error.

At this point, I'd be pulling out my 'scope. There are just too many things that could be wrong--absent more detailed information, it's like pitching horseshoes in the dark to find the cause.

For example, the BIOS ROM could be bad. The CPU could be bad. The CPU clock could be bad. You could have a cold-solder joint on the planar. The list is very long.

Even an inexpensive logic probe would be useful at this point just to determine which signal lines are wiggling and which aren't.
 
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Mobo & test equipment

Mobo & test equipment

Ok, even I have to admit it looks like a motherboard problem.

Could you describe what kind of test equipment you have, or can get your hands on ?
There's not much point in throwing suggestions your way if we don't know what kinds of tools you have access to, and also if you have any spare parts.

Could you take some pictures of the board & post them, just to get idea if it's in bad shape or not ? (If you don't know how, you can look it up under the FAQ)

patscc
 
Posting pictures shouldn't be a problem, I will post them tomorrow in the evening, cause I don't have so much time now...
I think I do not have any more spare parts but I will look around if I can find something..

Testing Equipment... oh... I do not have really much... But if you can tell me what I need I can look for these tools... Or perhaps you could tell me what can be useful or necessary.
 
So it's a faulty motherboard (and not faulty in a way that excessively loads the power supply).

As Chuck wrote, the possible reasons are many. Swapping out the CPU and the two BIOS ROMs is what I'd do first. Then I'd be bringing out my oscilloscope now to check some basics, e.g. clock generation, etc. and then I'd be trying the custom diagnostic ROMs I've been creating.

As an aside, writing the custom diagnostic ROMs hasn't been as straightforward as I thought. For example, in the 'first 16K' RAM test, I eventually discovered that to get my POST card to display something, I had to disable the DMA controller first. You don't see IBM doing that in their 5170 code.

I'm sure elton121 doesn't have access to an EPROM burner. Yes/no? Anyone prepared to send him some 27256s containing a 5160 BIOS (preferably the last revision)? It has to be expected that a cost is involved.
 
I don't know where elton121 is located. If in the USA, I might be willing to burn both a 5160 BIOS and a diagnostic ROM for him.

But something tells me he's overseas.
 
Yes, as you can already read from my first post and see on my bad English, I'm not from USA ;) I'm from Germany ;)

No I do not have access to an EPROM burner...
What do you think I need? I'm not really familiar with all these things and do not even know much about it as you can see ;) do you mean the 2 "things" (sorry, don't know the english word), next to the CPU (I think one of them is for the BIOS?!)? As I already said, I'm going to upload some pics and perhaps you can then describe what you think I need ;)
 
Hello,

what kind of monitor do you use and what kind of GFX-Card is in the system?



Oder auf Deutsch: Welchen Monitor und welche Grafikkarte sind verbaut ?


Greetings from Hamburg, Germany
Marc-Tell
 
Clock & Power good

Clock & Power good

Well, here's a way to see if your system clock starts up. Take a regular, portable FM (UKW) radio, and tune it to the lowest band, 87.50 Mhz. This is close to the 6th harmonic of the PC's clock crystal. (If you have a short-wave capable radio, try any multiple of 14.31 Mhz)

Hold the antennae near the small chip labelled 8284A. This is near the connector from the power supply to the motherboard.
Turn the volume up. Turn the PC up. You should hear an increase white noise, and a few high-pitched wines mixed in with the noise. Now turn the PC off. The noise should lessen, and the whine should go away.

If this happens, your system clock is quite probably starting up.
Since you checked voltages earlier, it sounds like you have access to a volt meter.
When the system is on, measure the voltage from P8, pin 1 to ground. This is the "Power Good" line. It tells the motherboard that the power coming from power supply is good, which is a good starting point. It should read about 5 volts. P8 is the right half of the power connector, it's the one closes to the back of the case.

elton121 sagte...which has always worked before
Click to expand...

I don't think anyone's asked this question before, but about how long ago was it that it was last working ?

patscc
 
status codes

status codes

per said...Keyboard port. Checkpoint bytes
Click to expand...
Good idea. I'm going to hook up a scope to pins 1 & 2 of the keyboard port to see if I can glean anything useful to pass along to elton121, assuming he can get hold of a 'scope. With a storage scope, you should be able to capture the pulse train of the code, but even with a regular one, you should still be able to see something usefull.

patscc
 
Even if you do not have an oscilloscope or logic analyzer, a good inexpensive investment is a logic probe--in particular, one that not only indicates high and low voltage levels, but can also indicate pulses. They can be very inexpensive and are probably available at most electronics stores that also sell ICs and other components.

Here's a typical one. I'm not recommending this one, just showing it as an example.

That "pulse" feature can tell you all you need to know about what lines are "wiggling" and which ones are not.
 
patscc said:
Good idea. I'm going to hook up a scope to pins 1 & 2 of the keyboard port to see if I can glean anything useful to pass along to elton121, assuming he can get hold of a 'scope. With a storage scope, you should be able to capture the pulse train of the code, but even with a regular one, you should still be able to see something usefull.
Click to expand...

One time, I really got nutty and used a parallel printer port on a second PC to serve as a keyboard--I wanted to switch the keyboard between running the system it was connected to and the one that was connected to the printer port. It worked fine (on a 5150)--what can I say? It was a slow day.

I could even see using a printer port between a keyboard and its host, intercepting and/or retransmitting keypress data. The XT keyboard uses very simple protocols.
 
poor man's dso

poor man's dso

I had another kooky idea, which, if it works, would be easier to do than getting a 'scope.
Here's the idea:
Via a simple divider, made up of something like a 10k & a 47k resistor, run the signal from pin 2 into the line in of a sound card and record the signal. Then, if you look at the waveform in something like Audacity, Sound Forge or Goldwave, you should be able to see the pulse train, and literally count the pulses, just like a PCM signal. In theory, at least. I'll post back after I've dug up a couple of resistors and a 1/8 jack cable, and given it a whirl.

patscc
 
Buy a P.O.S.T. card from China on feEbay for 12 bucks US, including shipping (the kind with the PCI AND ISA edge connectors).

In about 95% of the case when I use one of mine, it pinpoints the fault accurately.

It's just so much easier than buying/dragging out a scope, logic analyzer, what-have-you.

I agree that a logic probe is a handy device, especially if you have the SAM'S Computer Facts book for your computer which shows you what the logic states should be on every chip on the board in a known point in the startup sequence (usually just turned on).

However, if you're not lucky enough to have the SAM'S book, a logic probe alone may not be of much help, since, just because a pin is high or low, doesn't mean it's SUPPOSED to be high or low. This is where a signal injector comes in handy along with the logic probe. You can inject the input of a gate and see if the output is doing the righ t thing.
 
keyboard port

keyboard port

I ended up having to have the keyboard connected to get anything meaningful, and ended up taking the signal from pin 17 of the LS322 by the switch banks. Lots of lovely pulse trains. Unfortunately my DSO doesn't have enough memory to capture the whole thing.
Recording into a sound card is out, as well, as the pulse trains are dense enough to well exceed the upper frequency of sound cards. So much for quick & simple.
Oh well. <gruebel>,<gruebel>

Druid6900 said...P.O.S.T. card
Click to expand...
That's a great idea, but I thought XT's only wrote 5 codes to port 60h ?

00 or FF CPU register test failed
01 BIOS ROM checksum failed
02 System timer 1 failed
03 8237 DMA register Read/Write failed
04 Base 32K RAM failed

I must be getting something confused.

Druid6900 said...lucky enough to have the SAM'S book
Click to expand...
Are you ?

patscc
 
patscc said:
That's a great idea, but I thought XT's only wrote 5 codes to port 60h ?

00 or FF CPU register test failed
01 BIOS ROM checksum failed
02 System timer 1 failed
03 8237 DMA register Read/Write failed
04 Base 32K RAM failed

I must be getting something confused.
Click to expand...

It's an XT, what more do you need?

Are you ?
Click to expand...

No, I sold off a couple of hundred SAM'S Computer Facts Books on feEbay years ago. Most of them I didn't need and the ones I find that I do need, from time to time, I know where to find on the 'net. In fact, some of the people I sold them to were nice enough to scan them and put them on sites
 
Dead CPU

Dead CPU

Druid6900 said...It's an XT, what more do you need
Click to expand...
Well, OK. But I was hoping for something easy & useful for poor elton121.

I wonder if there's any hard-wired logic in the XT to force a 00 or FF at port 60h if the CPU is completely dead or missing ? Any thoughts on that ? While I do have a couple of POST cards floating around, they're probably in one of many boxes labeled "Vintage PC" that have yet to be unpacked.

patscc
 
patscc said:
Well, OK. But I was hoping for something easy & useful for poor elton121.

I wonder if there's any hard-wired logic in the XT to force a 00 or FF at port 60h if the CPU is completely dead or missing ? Any thoughts on that ? While I do have a couple of POST cards floating around, they're probably in one of many boxes labeled "Vintage PC" that have yet to be unpacked.

patscc
Click to expand...

I don't think so. I've examined the XT schematics for some time, and I see no traces of anything like that.
 
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