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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 22nd Nov 2019, 10:54 pm   #21
Sean Williams
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Default Re: Sun Microcomputer II Motortester 1215

Does rather smack of a dual rail op-amp not seeing both rails....

Have to say probe amputation was a real issue - especially on the 2l petrol transits.... that fan really needed a better cowl

Be great to see it all behaving properly again.
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Old 24th Nov 2019, 2:00 pm   #22
Zelandeth
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Default Re: Sun Microcomputer II Motortester 1215

Quote:
Originally Posted by Sean Williams View Post
Does rather smack of a dual rail op-amp not seeing both rails....

Have to say probe amputation was a real issue - especially on the 2l petrol transits.... that fan really needed a better cowl

Be great to see it all behaving properly again.
I've had my knuckles firmly smacked by the one in my Merc T1 on a couple of times!

Had all of the analogue cards out yesterday for a visual inspection and to see if there were any further tantalum caps hiding on those.

Note: there are two identical boards used for the horizontal and vertical deflection amplifiers... I've only photographed one as they're identical and neither show any signs of damage.

Only real faults I've found there were one toasty looking resistor on the volts/ohms card, though it measures absolutely spot on. Being a slightly higher power type by the looks of it I do wonder if it's just discoloured from 30+ years of warm running rather than an actual fault. Without a schematic I'm just going to need to keep an eye on it I think. Other fault was one dry jointed cap on the amps/temp board. Other than that they're all just wanting a good blow over with the air line courtesy of living right next to a fan.

The temperature readout is behaving slightly more sensibly now I've got the right probe plugged into it. There's still an offset, but it's at least responding to changes in temperature on the probe.
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Old 24th Nov 2019, 2:01 pm   #23
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Default Re: Sun Microcomputer II Motortester 1215

Photos of the remaining analogue boards attached.
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Old 24th Nov 2019, 5:24 pm   #24
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Default Re: Sun Microcomputer II Motortester 1215

I remember those boards, we were only supplied with spare boards to "board swap" repairs, no diagrams and no help, all boards to be returned to Sun for >repair<, repairing boards by field technicians was discouraged!! the cost of each board was 300-500 + service charge/callout + VAT from Sun or its agent in Manchester (name withheld). There are no diagrams or information available, so good luck, i'm following this thread with interest.
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Old 24th Nov 2019, 5:31 pm   #25
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Default Re: Sun Microcomputer II Motortester 1215

The grey-sleeved electrolytics - marked "IC" [Illinois Capacitor] are sometimes problematic - I've had to replace these in various bits of kit over the years due to loss-of-capacity/clear signs of 'venting' through the rubber end-bung.
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Old 24th Nov 2019, 6:46 pm   #26
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Default Re: Sun Microcomputer II Motortester 1215

Doesn't really surprise me that Sun kept careful guard on the service data. I imagine the servicing and service contracts were probably far more lucrative than the sale of the actual machines.

Cheers for a heads up on those caps. Most of the others at least look to be good quality ones which I've rarely had too much trouble with before.

I took the opportunity to grab some proper photos of all the digital boards this evening and carefully reseated every socketed chip.

Photos are:

1. "P/P" - Pre-processor.
2. "MEM1" - ROM.
3. "CPU" - Self explanatory.
4. "I/O" - ...Also self explanatory.
5. "MUX" - A-D conversion looks to be the main job here.
6. "CRT" - handles producing a composite video signal to be sent to the display.
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Old 24th Nov 2019, 6:48 pm   #27
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Default Re: Sun Microcomputer II Motortester 1215

...and the final image I didn't have room to attach to the last post.
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Old 24th Nov 2019, 7:08 pm   #28
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Default Re: Sun Microcomputer II Motortester 1215

There's nothing there that looks even remotely difficult to reverse-engineer if you had the time and inclination.

Thinking about the fault, it seems that the functions that use the ADC are playing up, the ones that work probably don't use it (things like timing measurements). So that's where I'd start, check the input and reference (and supply voltages) in that area.
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Old 24th Nov 2019, 7:10 pm   #29
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Default Re: Sun Microcomputer II Motortester 1215

An interesting thread. I enjoy reading about "out of the ordinary" stuff. Makes a change from record players and DAC90A's.

I look forward to reading of a successful conclusion.
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Old 24th Nov 2019, 10:22 pm   #30
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Default Re: Sun Microcomputer II Motortester 1215

Now we're getting somewhere.

Having the cards out and reseating the various ICs has rewarded us with a working voltmeter.

The attached screenshot shows one column (right) with a car battery attached to the relevant leads captured using the data hold function, the second column (left) shows it with the leads shorted together. Had to do that as it can detect when they're not connected to anything and just blanks the display for that value out.

Definitely making progress, as this was just showing garbled nonsense before.
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Old 25th Nov 2019, 12:59 am   #31
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Default Re: Sun Microcomputer II Motortester 1215

I had my suspicions all along that it might just be a poor connection on the ADC or MUX boards that was breaking the analogue readings!

Are the exhaust gas readings sane now, or are they still outrageously wrong?
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Old 25th Nov 2019, 1:29 am   #32
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Default Re: Sun Microcomputer II Motortester 1215

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Originally Posted by julie_m View Post
I had my suspicions all along that it might just be a poor connection on the ADC or MUX boards that was breaking the analogue readings!

Are the exhaust gas readings sane now, or are they still outrageously wrong?
It's still refusing to pass the calibration, so doesn't actually show any readings, hence the *** shown in the above screenshot.

Next up will probably be to give all the connections between the gas analyser and the computer itself a going over, then see where we end up.
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Old 26th Nov 2019, 3:39 am   #33
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Default Re: Sun Microcomputer II Motortester 1215

Is this the point where I should cue the classic mad scientist manic laughter?

Probably not...but it proves that my sneaky plan to use the computer display for a dual purpose to help this unit be even more useful in the 21st century garage is a sound one.

The display is actually a LOT sharper than the photo makes it look...the camera unsurprisingly wasn't impressed with trying to capture an image from an interlaced CRT display.
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Old 27th Nov 2019, 12:42 pm   #34
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Default Re: Sun Microcomputer II Motortester 1215

Cute! I'd keep it intact though. I've been following this with interest. It really is a nice piece of kit.

D
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Old 27th Nov 2019, 2:40 pm   #35
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Default Re: Sun Microcomputer II Motortester 1215

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Cute! I'd keep it intact though. I've been following this with interest. It really is a nice piece of kit.

D

Oh don't worry. There will be nothing destructive done and the original functions of the machine will be utterly unaffected - being able to use it as intended is key to it having a home in my garage. The idea here is purely to help the thing be a little more relevant in the 21st century. The only visible signs of changes will be a video source selection switch, and even that can be fitted through a blanking bung by the remote control socket so I don't need to drill a hole in the case.

The idea of having a decent sized display in the garage I can stick manual pages, wiring diagrams etc on other than my phone is something that I've had in mind for a while now.

The idea would be to set up a small single board computer (Raspberry Pi most likely as I'm familiar with it) inside and have a switch to allow me to choose the video source.
The monitor is only connected to the computer by a single twisted pair carrying composite video, so breaking into the signal path is trivially easy. There's even a convenient passthrough power lead available which would have originally fed the optional printer.

I wouldn't consider hacking the original machine around in any way that was detrimental to it.
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Old 29th Nov 2019, 6:43 pm   #36
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Default Re: Sun Microcomputer II Motortester 1215

Quote:
Originally Posted by Zelandeth View Post
Is this the point where I should cue the classic mad scientist manic laughter?

Probably not...but it proves that my sneaky plan to use the computer display for a dual purpose to help this unit be even more useful in the 21st century garage is a sound one.
I noticed a few empty ROM sockets and thought that it would be appropriate to include a Pong mode.
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Old 4th Dec 2019, 6:09 pm   #37
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Default Re: Sun Microcomputer II Motortester 1215

I have the (stripped of anything useful) cards from one of these testers in my scrap PCB crate awaiting the smelters if you want them.

Like you I got one of these testers, years ago, and tried to make it work for the fun of it. Age and working environment had not been kind and while it booted the display was very garbled and I ended up scrapping it.

The base cabinet (which you appear to be missing) from my example is however still going strong as my dad's tool storage chest !!
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Old 5th Dec 2019, 3:14 am   #38
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Default Re: Sun Microcomputer II Motortester 1215

Quote:
Originally Posted by Zelandeth View Post
Doesn't really surprise me that Sun kept careful guard on the service data.
I started servicing these sorts of things from the MEA1500 on for a while (OK when new but a nightmare once they got a bit older or they sent you the wrong version replacement board) and do actually have all the schematics for one variation of it, so the data was available if you had the right contacts.

The most common problems I found was (as you have found) IC sockets (loss of tension), connectors (same) and dry joints.

Both monitors were renowned for doing in the vertical output transistors once a particular cap went faulty and the HV modules seemed to go through a bad patch at one stage too.

Chopped, severed, mutilated cords/probes was next on the list which often led to component faults on the boards.

High energy ignition systems also used to play havoc with unmodified machines as well.

One other thing to watch out for is if it has metal bodied cooling fans rather than plastic ones, they break down (electrically) to the frame and randomly blow fuses/breakers/rcd's.

All I can say is, glad I don't touch them anymore (apart from a friends SUN 500).
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Old 8th Dec 2019, 3:31 am   #39
Zelandeth
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Default Re: Sun Microcomputer II Motortester 1215

It looks like everything is now working to at least some extent aside from the gas analyser - though I think that may be an optical alignment issue rather than electronic, as the bolts holding the detectors (photodiodes) in place were loose.

I'm guessing the way to get that set up will be to hang a scope across the detector and wiggle things around until you have an even sine wave showing the reference and measured signals to be as closely balanced as possible. Either that or substitute the IR source temporarily with a visible light source and use Mk I Eyeball to get it even.

Operationally speaking it seems to otherwise generally be behaving. We've got some sticky latching buttons and a slight waving motion on the monitor so a bit of work still needs done...but we're moving in the right direction it feels like.

I do still have the base cabinet for it, we just separated them to make it vaguely possible to lift it over the threshold into the house...as a single assembly it would have just been far too heavy for two people.

Now I'm thinking about it, I may well get it back on the base tomorrow as it will be far more pleasant to work on it standing up than cross legged on a freezing cold tile floor...
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