22nd Mar 2021, 5:30 pm | #81 | |
Octode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 5:40 pm | #82 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: The Transam Triton Personal Computer
74LS165 is a shift register, 74LS161 is similar to 74LS163, but has asynchronous reset.
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22nd Mar 2021, 5:44 pm | #83 | |
Octode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 5:47 pm | #84 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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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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22nd Mar 2021, 5:50 pm | #85 | |
Octode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 5:53 pm | #86 |
Pentode
Join Date: Mar 2021
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Re: The Transam Triton Personal Computer
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22nd Mar 2021, 6:10 pm | #87 | |
Octode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 6:29 pm | #88 |
Pentode
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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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22nd Mar 2021, 6:46 pm | #89 |
Octode
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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. |
22nd Mar 2021, 6:59 pm | #90 |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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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. |
22nd Mar 2021, 7:16 pm | #91 | |
Pentode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 7:20 pm | #92 |
Octode
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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 |
22nd Mar 2021, 7:34 pm | #93 | |
Pentode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 7:56 pm | #94 |
Octode
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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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22nd Mar 2021, 7:57 pm | #95 |
Dekatron
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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. |
22nd Mar 2021, 8:01 pm | #96 |
Dekatron
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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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22nd Mar 2021, 8:29 pm | #97 | |
Pentode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 8:53 pm | #98 | |
Pentode
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Re: The Transam Triton Personal Computer
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22nd Mar 2021, 9:16 pm | #99 | ||
Octode
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Re: The Transam Triton Personal Computer
Quote:
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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22nd Mar 2021, 9:23 pm | #100 | |
Octode
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Re: The Transam Triton Personal Computer
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