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IMC Traveller 286 - locks up shortly after boot

tingo

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I have described the IMC Traveller 286 in another thread.
Anyway the machine locks up shortly after boot.
When the machine is "cold" (has been powered off for a while, not used) I can use it for a minute or two before it locks up.
When the machine has been just turned off, it refuses to boot at all.

How can I figure out what the problem is?
Should I start with the PSU or the motherboard?
 
On modern PCs, that type of behavior almost screams "overheat." I don't really know anything about the construction of a Traveler, but if there's even one fan on it, I'd check that first to see if it's gummed up.
 
Okay, I have never seen an IMC system so some of my comments may be completely wrong but based on a different lunch pail portable, some problems are caused by a combination of heat and vibration.

If you can open the system up, see if any chips have loosened in their sockets or if the expansion cards have slipped loose. Reseat any if possible.

I would also suggest trying to boot the system with the expansion cards removed and the hard drive unpowered. That minimizes both heat and vibration. If the system keeps running longer, that would give a good path for fixing the system.
 
On modern PCs, that type of behavior almost screams "overheat." I don't really know anything about the construction of a Traveler, but if there's even one fan on it, I'd check that first to see if it's gummed up.

Absolutely "overheat" should be the first priority to look at. Check all the air ducts first then the fan for the CPU. My God I have to take the Compaq completely apart to get to the fan of the CPU. Then I saw the heat transfer compound was in black color. Never see black before so I scraped it off and replaced with the white or silver compound. Compaq is working fine now.

Dougtronics
 
It's a 286...I've never seen a 286 that had a heatsink, or even a case fan aside from the PSU fan.

The issue about not booting up shortly after turning it off MIGHT be unrelated; in my (not extensive, but certainly not limited) experience, the majority of "AT-type" power supplies need somewhat of a resting period between power on sessions. Some power supplies will turn on but the system won't POST, some of them won't turn on at all. This time period seems to usually be around 10 seconds but I saw one that was closer to 30...how long are you waiting before turning it back on?

As for your main issue, it does sound like a heat issue, but these CPUs didn't have heatsinks for a reason: they don't need them, because they are able to handle their normal operating temps quite capably.

A possibility - maybe the PSU becomes unstable after a certain period of time and the motherboard freezes up because of an undervoltage somewhere?
 
On modern PCs, that type of behavior almost screams "overheat." I don't really know anything about the construction of a Traveler, but if there's even one fan on it, I'd check that first to see if it's gummed up.

There is a fan in the PSU module. This fan is working, and wasn't very dusty either (I cleaned the dust away).
 
If you can open the system up, see if any chips have loosened in their sockets or if the expansion cards have slipped loose. Reseat any if possible.
I have pressed on the socketed chips - it didn't seem like any of them were loose. All expansion cards have been reseated (but this system is quite nicely put together - the screws on expansion cards were sealed with loctite or something like it), and I re-plugged all cables. Didn't seem to make any difference.

I would also suggest trying to boot the system with the expansion cards removed and the hard drive unpowered. That minimizes both heat and vibration. If the system keeps running longer, that would give a good path for fixing the system.

I could take out the hard drive at least.
 
It's a 286...I've never seen a 286 that had a heatsink, or even a case fan aside from the PSU fan.
You are correct - there is only the PSU fan.

The issue about not booting up shortly after turning it off MIGHT be unrelated; in my (not extensive, but certainly not limited) experience, the majority of "AT-type" power supplies need somewhat of a resting period between power on sessions. Some power supplies will turn on but the system won't POST, some of them won't turn on at all. This time period seems to usually be around 10 seconds but I saw one that was closer to 30...how long are you waiting before turning it back on?
I'm waiting between 1 - 3 minutes.

A possibility - maybe the PSU becomes unstable after a certain period of time and the motherboard freezes up because of an undervoltage somewhere?

I'll have to check this.
 
Testing without hard drive

Testing without hard drive

Ok, so I removed the hard drive (it is a Seagate ST-125) and powered on the machine. No joy - it still hangs / locks up within a minute.
The controller card controls both the hard drive and the floppy drive so I cant remove that. (The floppy dribe is a Teac FD-55GFR-570-U).
I waited a couple of minutes and turned the machine on again; it works, but instead of locking up it rebooted. On reboot it locked up.
 
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Battery

Battery

The battery is a blue barrel shaped thing between the keyboard connector and the power connector on the main board. The battery is labeled:
3/GP60K
3.6V
60mAh

And it has voltage - my universal meter reads about 3.8V
Also it looks very fine, doesn't look like it has leaked.
 
Psu

Psu

The PSU is marked "DC OUPTUT 200W" next to where all the internal cables come out of it.
It is avery compact unit.
Thhe fan is a SPROFAN, model SJ-80Y12B, DC 12V, 0.11A
 
PSU: I need to check the voltages,
Is it possible (and safe) to power up the PSU without anything else connected to it? Or will I damage the PSU if I do that?

(Modern PC PSU's likes a load to work, but I don't know about this one)
 
Given you mentioned the "choice" between a spurious reboot or lock-up, possibly there's bad RAM in there too? But it could still be an unstable PSU in any case...

Is it possible (and safe) to power up the PSU without anything else connected to it? Or will I damage the PSU if I do that?

A lot of them will just not run without a load. A long time ago I do remember hearing that you "must" have a load (even if just a resistor) for some reason I can't recall. In any case, running loadless may or may not show you a possible power problem. But it should be fine for a couple minutes test I would assume...
 
PSU - voltages

PSU - voltages

Well, I finally found time to measure the voltages today.
First, I measured the voltages without anything connected to the PSU, the +5V seemed ok, but the +12V was only 8.49V. So this PSU isn't designed to work without a load.

I connected the PSU to the machine, and performed a new set of measurements. (All measurements done with a digital voltmeter / universal instrument)
+ 5V = 5.07 V
+ 12V = 12.09 V
- 12V =- 12.05 V (measured on the motherboard power connector)
So, the voltages seems ok.
 
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Ram

Ram

The RAM is divided in two banks: "BANK 0" and "BANK 1". Each bank consists of two rows of nine chips. All chips in sockets.
Bank 0: have chips of type M41256A-12 from OKI
Bank 1: have chips of type KM4164B-12 (a Korean manufacturer, I can't decode the logo)

How do I find out if any of the RAM chips are bad?

Another question: does these chips add up to 640K?
 
I would also suggest trying to boot the system with the expansion cards removed and the hard drive unpowered. That minimizes both heat and vibration. If the system keeps running longer, that would give a good path for fixing the system.

I tried running the system with only the LCD controller card in ti, and using the keyboard and screen as a diagnostic tool (when the keyboard doesn't respond any more, the computer has locked up).
However, it sems that it freezes / locks up just as soon as it does with the controller and floppy drive connected.
 
I tried running the system with only the LCD controller card in ti, and using the keyboard and screen as a diagnostic tool (when the keyboard doesn't respond any more, the computer has locked up).
However, it sems that it freezes / locks up just as soon as it does with the controller and floppy drive connected.

I wonder if it's a bad capacitor on the disk controller? One of my Apple II clones stopped working after a few seconds. The cause was a capacitor that failed after it heated up.

Tez
 
The RAM is divided in two banks: "BANK 0" and "BANK 1". Each bank consists of two rows of nine chips. All chips in sockets.
Bank 0: have chips of type M41256A-12 from OKI
Bank 1: have chips of type KM4164B-12 (a Korean manufacturer, I can't decode the logo)

Another question: does these chips add up to 640K?
Code:
41256 = 256K x 1 bit
 4164 =  64K x 1 bit

Each bank is 18 chips wide: 16 data bits + 2 parity bits.

Bank 0 therefore would be 16 x 256K bit = 4096K bit = 512 KB
Bank 1 therefore would be 16 x  64K bit = 1024K bit = 128 KB
                                                     --------
                                                      640 KB
 
I wonder if it's a bad capacitor on the disk controller? One of my Apple II clones stopped working after a few seconds. The cause was a capacitor that failed after it heated up.Tez
My reading of Tingo's post was that there's was no noticeable change with the controller removed.
 
How do I find out if any of the RAM chips are bad?
You could first try running the board with the second bank removed to see if the problem cause is in the second bank.
Of course, use anti-static procedures when removing the chips (you don't want to create dead/intermittent chips).
 
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