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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 Mar 2021, 5:30 pm   #81
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Default Re: The Transam Triton Personal Computer

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Originally Posted by GeraldSommariva View Post

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 ?
My odd VDU board, with a seemingly equivalent ET9365APm uses a 74LS165 - If you have one, I recall the LS165 is similar to LS163 but need to check pinout / etc.


So was Pin10 of the VDU IC, with just its supply and oscillator pins patched across, going high at all?
If not, then it does look like that may have unfortunately failed.

From the timing diagrams on the VDU datasheet, it wasn't clear if nINI goes high for a fixed period, determined by divided down 1.008MHz osc. (most likely) or whether the VDU IC might count for exactly 64 cycles of the 1.6MHz external clock before driving nINI low again.
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Old 22nd Mar 2021, 5:40 pm   #82
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Default Re: The Transam Triton Personal Computer

74LS165 is a shift register, 74LS161 is similar to 74LS163, but has asynchronous reset.
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Old 22nd Mar 2021, 5:44 pm   #83
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Default Re: The Transam Triton Personal Computer

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Originally Posted by GeraldSommariva View Post
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
That does sound rather serious - Having -12V on the datalines is unlikely to be good for anything else connected to these, so could cause lots of damage.
And is most likely due to a short to -12V rail in an IC that uses this power rail, on the keyboard.
Although it could be due to the loss of a positive supply rail, if the IC's using these are biasing the lines relative to that

I can't seem to find any info on that obscure Keyboard controller / encoder IC. I wonder if it's equivalent to a more stand AY-x-xxxx one or whether it's a custom microcontroller etc.
And the keyboard itself is now rather uncommon - do you have any documentation that came with it? - All I can find is:
https://deskthority.net/wiki/Micro_Switch_SD_Series

Last edited by ortek_service; 22nd Mar 2021 at 5:55 pm.
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Old 22nd Mar 2021, 5:47 pm   #84
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Default Re: The Transam Triton Personal Computer

IC63 pin 1 is held high, so you could try a 74LS161 if you have one of those.
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Old 22nd Mar 2021, 5:50 pm   #85
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Default Re: The Transam Triton Personal Computer

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74LS165 is a shift register, 74LS161 is similar to 74LS163, but has asynchronous reset.
Thanks - I had assume they'd used the LS165 on my odd board, as it was the only TTL IC in that number range that was next to the external oscillator parts for the VDU IC. But I have just spotted an LS163 on it, across the other side of VDU IC's pins / the PCB - not where you'd expect it .
So I thought they did copy the standard reference circuit from the datasheet on my odd VDU board, but they had done a bit of an strange layout

However, I've just buzzed-out the connections and found they've actually connect the Phase1 VDU IC Pin9 Ext. clock input via a 1k8 resistor to pin 9 of a nearby 74LS175 Quad Flip-flop. So it seems if they've made their own divider circuit from Flip-Flops rather than using the 74LS163 on this one.

Last edited by ortek_service; 22nd Mar 2021 at 6:06 pm.
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Old 22nd Mar 2021, 5:53 pm   #86
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Default Re: The Transam Triton Personal Computer

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Originally Posted by ortek_service View Post

So was Pin10 of the VDU IC, with just its supply and oscillator pins patched across, going high at all?
If not, then it does look like that may have unfortunately failed.
No Pin 10 is low all the time both in circuit or with my patch configuration.
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Old 22nd Mar 2021, 6:10 pm   #87
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Default Re: The Transam Triton Personal Computer

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Originally Posted by GeraldSommariva View Post
Quote:
Originally Posted by ortek_service View Post

So was Pin10 of the VDU IC, with just its supply and oscillator pins patched across, going high at all?
If not, then it does look like that may have unfortunately failed.
No Pin 10 is low all the time both in circuit or with my patch configuration.
Oh dear! - It does then rather look like the VDU has unfortunately died.

It's rather odd that the extra oscillator / divider IC's have also failed
- It seems like there must have been something quite catastrophic occurring (Hopefully not a large overvoltage on the +5V rail, that powers all of these, as that could have taken out quite a lot)
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Old 22nd Mar 2021, 6:29 pm   #88
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Default Re: The Transam Triton Personal Computer

Just had some power dips here its taken out my Triton PSU and my 6 port USB power supply I use to power my Raspberry PI Farm. so back to square one with the power supply.
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Old 22nd Mar 2021, 6:46 pm   #89
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Default Re: The Transam Triton Personal Computer

Odd for a power-dip to cause that much damage - May have actually been a power-spike/surge that occurred, which apparently quite commonly occur with dips before / after, as power distribution network responds to it.

And unlucky to have your Triton PSU fail again so soon!

I'm thinking that some over-voltage protection shunts on the PSU rails wouldn't be a bad idea, to guard against future failures, as some of the specialised IC's are quite rare expensive.

The SFC / SFF / CRT 96364 VDU IC (and ET9364AP equivalent?) don't seem to be available for any cheaper than the £18 you'd found - Not even from far-east suppliers, without getting quotes from sourcing companies.
But I did discover these associated links, that may be of interest:

https://www.vintage-radio.net/forum/...=162766&page=2
- Discussions on the SoC MK14 VDU board, that uses the same IC and was originally unobtainable any more, so alternative replacements discussed.

http://www.flaxcottage.com/ComputingToday/7909.pdf
- Has article on Triton, and adverts for it / generic Keyboards+encoders etc.

https://stardot.org.uk/forums/viewtopic.php?t=9821
- A similarly vintage 8080 computer (picked up for free, from Newbury radio rally I went to), that uses the same VDU IC and may have been an Altair clone / ran Altair BASIC.
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Old 22nd Mar 2021, 6:59 pm   #90
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Default Re: The Transam Triton Personal Computer

Switch-Mode power supplies are odd things, they will try to maintain their output wattage into the load, so if the input voltage briefly halves for some reason they will pull double the normal amount of current from the mains to try to compensate (This is also the reason it's a really, really bad idea to slowly wind up the mains voltage into anything which has an SMPSU).

More modern SMPSUs probably have undervoltage protection circuits so they don't kill themselves by trying to maintain their output during a bad brownout, but early SMPSUs probably didn't have this.

If you are lucky it may just have blown the mains-side fuse.
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Old 22nd Mar 2021, 7:16 pm   #91
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Default Re: The Transam Triton Personal Computer

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Switch-Mode power supplies are odd things, they will try to maintain their output wattage into the load, so if the input voltage briefly halves for some reason they will pull double the normal amount of current from the mains to try to compensate (This is also the reason it's a really, really bad idea to slowly wind up the mains voltage into anything which has an SMPSU).

More modern SMPSUs probably have undervoltage protection circuits so they don't kill themselves by trying to maintain their output during a bad brownout, but early SMPSUs probably didn't have this.

If you are lucky it may just have blown the mains-side fuse.
Look's like I am not so lucky check both fuses and thay are both good, and there is the +18v drive voltage which was the problem last time.

I think I might ditch this supply as it is old and as you say probably has no under voltage protection circuits.


What about using a desk top pc power supply ?
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Old 22nd Mar 2021, 7:20 pm   #92
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Default Re: The Transam Triton Personal Computer

Although many will work down to 90V, for worldwide use, so are self-adapting to a degree. - Although some have a link to re-arrange the centre-tapped HT reservoir capacitor etc.

Winding the input voltage up slowly, with a variac, was quite a common servicing technique to help prevent it going bang if there was still a fault.
However, this is mainly done with little load / without full load on it.

I has been said that an SMPSU is a short across the mains for short periods, and so is only a few ms from self-destruction in the event of certain faults.

Original PC PSU's often had overvoltage protection shutdown- As I discovered, when I disabled it to try to find out why it wasn't working, and then discovered that the original ones needed a minimum load so used a large power resistor in a metal cage if you didn't have the HDD fitted! - So much for higher efficiency
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Old 22nd Mar 2021, 7:34 pm   #93
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Default Re: The Transam Triton Personal Computer

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I'm thinking that some over-voltage protection shunts on the PSU rails wouldn't be a bad idea, to guard against future failures, as some of the specialised IC's are quite rare expensive.
Good news All my rare IC are mounted in sockets and they were out of the board at the time of the power supply failure, apart from the VDU memory which for some reason is soldered in.

At the time I was working through the rest of the TTL logic but I do think I will need a new VDU chip.
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Old 22nd Mar 2021, 7:56 pm   #94
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Default Re: The Transam Triton Personal Computer

That is good news - I found it fairly easy to get VDU memory so apart from the desolder problem that would not be a total loss. Shame about the PSU though.
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Old 22nd Mar 2021, 7:57 pm   #95
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Default Re: The Transam Triton Personal Computer

Ortek, I agree that most modern SMPSUS are as happy to work from 100V as 240V but the one under discussion clearly comes from an earlier era, and my warning against using a variac to ease up the supply input especially applies to early-period SMPSUs intended to run from a fairly narrow input voltage range.

The only drawback with PC power supplies is that they can supply a huge amount of current especially from the +5V output, so if anything ever goes badly wrong on that PCB you could see tracks being blown off rather than the PSU just calmly shutting down due to overload.

If you do use a PC power supply, you ideally need fuses in the output supply rails.
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Old 22nd Mar 2021, 8:01 pm   #96
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Default Re: The Transam Triton Personal Computer

I'm wondering if Tim might be able to consider testing the VDU IC as he has a working system? Some component suppliers, including some quite well known ones, have a habit of advertising ICs they don't actually have and only try to find them when anyone takes an interest.
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Old 22nd Mar 2021, 8:29 pm   #97
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Default Re: The Transam Triton Personal Computer

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Ortek, I agree that most modern SMPSUS are as happy to work from 100V as 240V but the one under discussion clearly comes from an earlier era, and my warning against using a variac to ease up the supply input especially applies to early-period SMPSUs intended to run from a fairly narrow input voltage range.

The only drawback with PC power supplies is that they can supply a huge amount of current especially from the +5V output, so if anything ever goes badly wrong on that PCB you could see tracks being blown off rather than the PSU just calmly shutting down due to overload.

If you do use a PC power supply, you ideally need fuses in the output supply rails.
Good point on the fuses looking at the PC power supply specs they can deliver a lot of power probably a bit over the top for my requirements.

As I was not intending to use the 3 x 8K memory cards stuffed full of 2114 static memory chips, My L7 basic and TRAP are in 8K Eproms so not a big load there.
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Old 22nd Mar 2021, 8:53 pm   #98
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Default Re: The Transam Triton Personal Computer

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Originally Posted by ortek_service View Post

I can't seem to find any info on that obscure Keyboard controller / encoder IC. I wonder if it's equivalent to a more stand AY-x-xxxx one or whether it's a custom microcontroller etc.
And the keyboard itself is now rather uncommon - do you have any documentation that came with it? - All I can find is:
https://deskthority.net/wiki/Micro_Switch_SD_Series
No I don't have any doc's, the hall effect switches work they give a pulse when you hit the keys, they are powered with +5v, so I wonder why you need the -12v
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Old 22nd Mar 2021, 9:16 pm   #99
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Default Re: The Transam Triton Personal Computer

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Originally Posted by GeraldSommariva View Post
Quote:
Originally Posted by ortek_service View Post

I can't seem to find any info on that obscure Keyboard controller / encoder IC. I wonder if it's equivalent to a more stand AY-x-xxxx one or whether it's a custom microcontroller etc.
And the keyboard itself is now rather uncommon - do you have any documentation that came with it? - All I can find is:
https://deskthority.net/wiki/Micro_Switch_SD_Series
No I don't have any doc's, the hall effect switches work they give a pulse when you hit the keys, they are powered with +5v, so I wonder why you need the -12v
I presume it must have originally come with some data, for knowing how to connect the keyboard you had to it. They don't seem to specify what Keyboard they originally used was - but I assume it needed -12V if they put it on the connector - And yours also needs this too, if your're measuring -12V on data lines (luckily buffered on board, so might help prevent too much damage)
I know that some of the GI AY-x-xxxx Keyboard controller/encoders, commonly used back then, needed another power-rail (+12V) besides +5V

I assume that, like the 8080, many PMOS devices back then needed extra rails, besides +5V, and the 'Keyboard Encoder' IC on your keyboard needed this (Although -12V is a bit off, as most only needed +12V / -5V). -12V was usually only required (along with +12V) for RS232 etc.

Regarding PSU's, their original Linear regulator one would have provided reasonably-low current limits on each rail - which probably works better than fuses on very high current rails. You could always use a micro-PC PSU, with lower output currents (although still a bit high) and those for external drives lack the -12V rail.

I suppose that if you don't need too much current off the +12 / -12V rails, then you could just use a small +/-12V output DC-DC converter for these + generate the -5V via the same zener-shunt regulator they used. And you could just use a modern small +5V output PSU (like a USB charger) for the +5V rail / input to a +/-12V DC-DC module, so that it all runs from just a +5V supply.

Last edited by ortek_service; 22nd Mar 2021 at 9:29 pm.
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Old 22nd Mar 2021, 9:23 pm   #100
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Default Re: The Transam Triton Personal Computer

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Originally Posted by SiriusHardware View Post
I'm wondering if Tim might be able to consider testing the VDU IC as he has a working system? Some component suppliers, including some quite well known ones, have a habit of advertising ICs they don't actually have and only try to find them when anyone takes an interest.
I suppose I could do that without too much risk as Gerald seems to find that they are all just low as long as it does not have a dead short Vcc 5v to Ground as obviously mine is a standard Triton PSU without any luxuries of protection against shorts...
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