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Old Nov 20 2019, 10:16 PM   #5130
Zelandeth
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Join Date: Mar 2013
Location: Milton Keynes
Gender: M
Fan of: Dragonsdawn
Now Reading: Working my way through the whole Pern series
Default Re: What is happening

Having decided that I'd had utterly enough of the outside world by about midday and having a complete failure to summon enthusiasm regarding doing anything actually useful...I spent a couple more hours fiddling around with the Sun.

Task number one was dealing with the vacuum hoses in the machine. I knew these had taken on the consistency of dried pasta and would disintegrate the moment I touched them. I wanted them changed before I started poking around as they were mostly still where they were meant to be...and I'd rather not play guessing games as to where they go.



By the time I was done, this is what was left. Plus a bunch of bits buried in the bottom of the case I'll need to get out with the vacuum cleaner.



Much better...



I discovered the hard way that that solenoid valve on the water purge line has mains on the (unsleeved) terminals even when the machine is off when it gave me a good old belt. Absolutely stupid not having the plug pulled before I did that.

Fiddly bit under the gas analyser done too. I'd missed the line heading off to the pressure transducer (far right out of frame) when taking this photo, it was sorted later.



With that sorted out I felt I could turn my attention to sorting the stuff which wasn't working. Two nuts removed allowed the whole front bezel to be removed...this vastly improved access.



This solves the problem of not being able to get to the computer.



This let me take a closer look at things. Not least figuring out what CPU the thing was running. I was expecting something 8-bit, maybe Z80 (half hoping actually as I've messed with them before and might have some hope of making heads or tails of the software) or 6000 series...Finding this however was rather a surprise.



That's a National INS8900D. For those not familiar with it, that's a 2MHz 16-bit processor... really wasn't expecting this to be a 16-bit machine... especially given it has its roots back in 1979...overkill?

The memory board. Yes, getting these EPROMs read and backed up is high on the priority list.



Not totally sure how, but I managed to forget to get photos of the MUX and I/O boards. I'll fix that later.

The board I was most interested in today however was this one.



The edge connectors actually looked pretty clean, though I gave it a scrub up anyhow. Based on prior experience though I figured the most sensible thing to do was to remove (carefully, using the right tool) each of the socketed chips and reseat them. Somewhat surprised to see a humble 555 timer in a socket. Have to wonder if they've had reliability issues with that IC.

With that done, slotted the card back in, powered on, and...



Rock steady display... I'll take that as a win. Having a display which would stay running for more than five seconds at a time I could let it complete the warm up process and run through the self test (having taken the opportunity to clean the CRT faces while it was in warm up as they were filthy).





Still surprised how sharp this display is... especially now there's not 1/8" of grime on it.

The faceplate was similarly filthy.



I wasn't surprised by the "service required" messages at the calibration screen. If I'd been abandoned in a cold damp shed since 2005 I'd be in need of a bit of TLC just the same.

I did a quick check on the gas analyser first to see if it would respond to a clean. First check though was of course to make sure that the IR source was "lit" correctly. The source here takes the form of a carbon rod, heated to the point where it just about glowing a really dim red (camera makes it look a little brighter than it is).



This is then focused via two parabolic mirrors onto a pair of sensors at the far end.







The spinning shutter at the source end allows the reading to be sampled from free air and the gas under test alternately.

It was given a really good clean (carefully...the mirrors are surface silvered) as the whole lot were filthy.

Sadly it didn't just miraculously come back to life...so further digging will be needed. Despite the errors,it was quite happy to continue into running mode.

First page you get is to enter the vehicle details - Number of cylinders, 2/4 stroke, and the timing offset. Once that is entered it presents you with the following screen.



The *** entries show where readings are missing due to the calibration issues. It will blank things out rather than potentially show erroneous data. This allows you to check things like the starter motor current, battery voltage during cranking. It also allows you to compare the current draw during each cylinder compression stroke to give a rough relative compression test to show if one pot is far lower than the rest.

Once that is completed, the engine running test page is presented.



I like the "bar graphs" drawn using the text...sneaky ways to do stuff like this without the overheads of bitmap graphics is half the fun of old kit from this sort of age.

Looks really the part with the front panel back in place.





So issues we need to look into:

[] Gas analyser inoperative.

[] Volt/ohm meter inoperative.

[] Temperature probe reading nonsense (see 160C reading above).

[] Suspicious of the vacuum reading.

[] Possible cap issues in the power supply as it shows a low line voltage warning at the calibration screen despite our line voltage being anything but low.

First port of call is going to be going over the machine end to end and reseating every socketed chip as I did on the CRT board, then see where we are. Will also make a point of checking for any signs of damage to the wiring where it enters the boom as it could be prone to chafing there.

Oh...and sort the dent in the power supply fan grill so it stops rattling before it drives me mad.



Interesting to see that the fans are actually 115V units...have to assume they're running from a step down transformer buried in that brick of a power supply.

Definitely making progress though.

Last random photo for the old tech enthusiasts...old computer equipment like this often displays interesting or odd artefacts on screen when rebooted. This is what the display shows on this for about a second when powered up.



Thought it might just be random nonsense in the RAM, but it seems to show the same every time.
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