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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 19th Mar 2021, 8:56 am   #61
ortek_service
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Default Re: The Transam Triton Personal Computer

Yes, I also had an intermittent earth-leakage trip on a Heating system, that I'd considered running off an isolation transformer so it could have it's own RCD and not take out the main RCD. Position of consumer unit makes it awkward to fit a separate RCBO circuit for it.

11.82V is still within the Output voltage spec. of a typical 7812: 11.5-12.5V (12V +/-4.2%), over the full-temperature range: eg: https://www.hobbytronics.co.uk/datasheets/L7812.pdf.

But you could ensure this is off-load voltage / measure direct at regulator, so that wiring-drops aren't a factor.
Also maybe check that the input to the 7812 is always > 15V, and there isn't a lot of ripple due to a failing smoothing capacitor between the rectifier diodes and it's input that could e causing it to dropout.

However, I have often measured the 12V rail as being closer to 11V on some PC PSU's, that only regulate the +5V rail and the +12V is just derived from a ratio-ed tapping on transformer without any post-regulation.
Some HDD were a bit fussy if this was a bit low, not starting it very well.
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Old 19th Mar 2021, 9:21 am   #62
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Default Re: The Transam Triton Personal Computer

What is the input voltage to the regulator? The unregulated input voltage needs to be at least 2V or more higher than the regulated voltage out on that type of regulator for the regulator to be able to 'regulate'. Also look at the input voltage to the regulator with a scope to make sure the input is moderately smooth DC and not ripple-rich.

If that's OK, remove the regulator and connect a variable voltage supply set initially to 14VDC to the input and GND terminals of the regulator and see what output voltage it produces when powered independently, outside of the SMPSU. If you still get <<12V, select another 7812.
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Old 19th Mar 2021, 4:48 pm   #63
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Default Re: The Transam Triton Personal Computer

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Originally Posted by SiriusHardware View Post
What is the input voltage to the regulator? The unregulated input voltage needs to be at least 2V or more higher than the regulated voltage out on that type of regulator for the regulator to be able to 'regulate'. Also look at the input voltage to the regulator with a scope to make sure the input is moderately smooth DC and not ripple-rich.

If that's OK, remove the regulator and connect a variable voltage supply set initially to 14VDC to the input and GND terminals of the regulator and see what output voltage it produces when powered independently, outside of the SMPSU. If you still get <<12V, select another 7812.
The input voltage is +15.5V, I found another 7812 on an old PCB fitted it and its giving +12.02 under load so I go with that.
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Old 21st Mar 2021, 6:23 pm   #64
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Default Re: The Transam Triton Personal Computer

Fired up the Triton main board today and as expected its not working.

Based on the first look see I have found a number of problems:-

The Keyboard is putting -12v on some of the keyboard buffer TTL data input pins IC49.

IC49 (74LS244) is holding DB8 to near zero but if the Keyboard is unplugged it returns to +5 but DB8 is connected to its input pin 11 even though the select pins and 19 are high.

The VDU chips seams dead IC61 (SFC96364) but there is a clock on pin 2, is this chip still available ?

Has anyone got a example of what the waveform should look like on pin 2 ?

This is going to be more of a challenge than I expected.
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Old 21st Mar 2021, 7:15 pm   #65
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Default Re: The Transam Triton Personal Computer

Those 244 chips are notorious for failing - with it just out of the board and the KB disconnected does that improve the situation? The keyboard pin header does have -12v as an output so maybe a short?

The VDU chip was available for about 18 from littlediode. They do not have a listing at the moment but, I am sure a contact will allow them to be found - they were SFF96364 not as per the ETI article - I have also seen them listed as CRT96364 - it needs to be an A for 50Hz https://www.littlediode.com

My Pin 2 is a fairly rounded 1MHz clock - photo attached.

I am sure Ian once said that the display appears blank if IC70 is faulty.
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Old 21st Mar 2021, 8:06 pm   #66
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Default Re: The Transam Triton Personal Computer

Is there a link to the original project / circuit diagram so we can follow along? I have an idea this was an ETI project, but that's as much as I know.

Regarding IC70, Gerald has said that he successfully verified the contents of his IC70 against the code that Tim posted (post #35).

Gerald, what specifically is making you think the video IC is dead?
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Old 21st Mar 2021, 8:23 pm   #67
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Default Re: The Transam Triton Personal Computer

Even cut down the article is too big for the 4Mb limit on the forum so here is my copy on the google drive extracted from the issue of ETI on worldradiohistory.

https://drive.google.com/file/d/1L09...ew?usp=sharing
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Old 21st Mar 2021, 8:32 pm   #68
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Default Re: The Transam Triton Personal Computer

Got that, thanks Tim. The detailed circuit description, which you don't always get with a commercial project, should be a big help.
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Old 21st Mar 2021, 8:32 pm   #69
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Default Re: The Transam Triton Personal Computer

If you want a quick video tour of a working one then...

https://www.youtube.com/watch?v=QLoXojMKH7U and https://www.youtube.com/watch?v=h-l5eP4cEFA

For a good history and background and another being restored...

https://www.youtube.com/playlist?lis...GsSlLytSfTVlp5
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Old 21st Mar 2021, 8:37 pm   #70
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Default Re: The Transam Triton Personal Computer

I'll follow those up.

Quote:
This is going to be more of a challenge than I expected
Just look at the outline of that board and think 'The fault, or faults, are somewhere inside this boundary. All I have to do is find them'.

Another thing you have in your favour is that the computer was (I hope) working when put into storage, is that the case?
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Old 21st Mar 2021, 8:45 pm   #71
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Default Re: The Transam Triton Personal Computer

As mentioned at start of the thread, it's in the ETI Nov 1978: With full copy here:
https://worldradiohistory.com/UK/Ele...1978-11-78.pdf

The Centre for Computing History website, list several manuals & Mag. articles
http://www.computinghistory.org.uk/d...ransam-Triton/
And has them to download - But unlike the MK14 ones, you have to pay a few 's to download each.

Gerald's put the VDU IC datasheet, amongst others on his website for this:
https://sites.google.com/view/transa...ets?authuser=0

I do have an odd video board that has an EF9364AP DIL28 IC on it, that looks like it may well be an equiv. along with the same 1.008MHz crystal. I haven't worked out what the board was for, but only cost me 1 (rather less than littlediode's price for that IC!)

Last edited by ortek_service; 21st Mar 2021 at 8:54 pm.
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Old 21st Mar 2021, 9:58 pm   #72
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Default Re: The Transam Triton Personal Computer

Quote:
Originally Posted by SiriusHardware View Post
Is there a link to the original project / circuit diagram so we can follow along? I have an idea this was an ETI project, but that's as much as I know.

Regarding IC70, Gerald has said that he successfully verified the contents of his IC70 against the code that Tim posted (post #35).

Gerald, what specifically is making you think the video IC is dead?
Here is the Scans of the circuits from ETI magazine and the Transam construction manual (116 pages in all so only a few pages).

Triton Circuits
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Old 21st Mar 2021, 10:03 pm   #73
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Default Re: The Transam Triton Personal Computer

Thanks Gerald, I seem to have the info coming at me from all directions now, it's like a digital custard pie fight.

So can I ask again, why do you think the VDU IC is faulty? Was the system put away in working order as far as you know?

Last edited by SiriusHardware; 21st Mar 2021 at 10:09 pm.
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Old 21st Mar 2021, 10:29 pm   #74
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Default Re: The Transam Triton Personal Computer

Quote:
Originally Posted by SiriusHardware View Post
Thanks Gerald, I seem to have the info coming at from all directions now, like a digital custard pie fight.

So can I ask again, why do you think the VDU IC is faulty? Was the system put away in working order as far as you know?
The Machine was working when I put into storage but that was some time ago now.

When I scope the VDI IC61 there is no activity on any of the pins other than pin2 OSC out the waveform is as follows:- Pin 2 output scope on ch2 0.2v x10 probe time base 0.5us.

I would say its the same as Tim's
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Old 21st Mar 2021, 10:39 pm   #75
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Default Re: The Transam Triton Personal Computer

If there is no line and field sync on pin 26 then you could be correct.

Also if the address lines into IC64 (4-7) and IC65 (8,29-22) are not cycling and there is nothing on 13,12 and 11 for the character row then it is likely failed.
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Old 21st Mar 2021, 10:55 pm   #76
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Default Re: The Transam Triton Personal Computer

It looks like you may also need an external clock source into the VDU IC, on Pin9 - Fed from IC63 (74LS163) - for it to function correctly.

The nInhibit Pin 10 is a bit confusing, as at first glance it would appear to be an input, but is actually an output that seems to control the external oscillator that feeds the IC63 counter/divider IC.
So worth checking that Pin 10 is actually high, else there won't be a clock source to it..
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Old 21st Mar 2021, 11:06 pm   #77
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Default Re: The Transam Triton Personal Computer

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Originally Posted by Timbucus View Post
If there is no line and field sync on pin 26 then you could be correct.

Also if the address lines into IC64 (4-7) and IC65 (8,29-22) are not cycling and there is nothing on 13,12 and 11 for the character row then it is likely failed.
I taken the chip out of circuit and jumper up the XT pin 2 now still has the 1Mhz out put but no activity on any other pin.

VDU Chip out of Circuit

In this config would we expect to see at least some activity ?

Also as you can see the marking on my chip have gone.
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Old 22nd Mar 2021, 12:08 am   #78
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Default Re: The Transam Triton Personal Computer

Yes, basically the 1.008MHz oscillator is divided down internally in the VDU IC to produce an external-oscillator gate output on pin10, that lets through 64 cycles (characters) of the (Phase)1 (Approx 1.6MHz) clock that increments its internal address counters.

So pin10 (nINI) should always be going high for a bit less than 64us horizontal line time.
- Otherwise, there won't be any character-clock pulses into pin9, from external gated source.

It could be possible that extra breadboard etc. capacitance / long wires to crystal could upset the 1.008MHz oscillator / stop it from working, but looks like you've checked that's still running.
You should actually also see a similar waveform at pin1, but it's likely that it may be a lower amplitude / putting 'scope probe on this could stall oscillator - So often need at least a x10 probe, to reduce capacitance of the probe down to around 10pF from typ. 65pF on x1
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Old 22nd Mar 2021, 10:33 am   #79
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Default Re: The Transam Triton Personal Computer

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Originally Posted by ortek_service View Post
Yes, basically the 1.008MHz oscillator is divided down internally in the VDU IC to produce an external-oscillator gate output on pin10, that lets through 64 cycles (characters) of the (Phase)1 (Approx 1.6MHz) clock that increments its internal address counters.

So pin10 (nINI) should always be going high for a bit less than 64us horizontal line time.
- Otherwise, there won't be any character-clock pulses into pin9, from external gated source.

It could be possible that extra breadboard etc. capacitance / long wires to crystal could upset the 1.008MHz oscillator / stop it from working, but looks like you've checked that's still running.
You should actually also see a similar waveform at pin1, but it's likely that it may be a lower amplitude / putting 'scope probe on this could stall oscillator - So often need at least a x10 probe, to reduce capacitance of the probe down to around 10pF from typ. 65pF on x1
I found IC62 dead (74LS86) and replaced with new one outputs are now good. It also looks like the /8 counter IC63 (74LS163) is dead too I don't have one to try.

With the VDU chip out, there is a clock on pin 2 of IC63 which can be adjusted by RV1 (Display Width) P15 RCO is at 1.5v and P12 OC is 0V.

So far that three TTL Chip dead ?
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Old 22nd Mar 2021, 3:38 pm   #80
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Default Re: The Transam Triton Personal Computer

The other problem I am having is with the keyboard putting -12v on the data lines, also the strobe out from the keyboard is sitting at a strange 2.1v.


The keyboard is from Micro Switch and the encoder chip is I think SW20457k
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