As discovered last episode, the SS10s are both still alive. Good ole serial console debug!
The problem running the SS10 off my adapted NV1 PSU is that the SS10 really wants 5.1V, not 5.0V. It will run rock-solid at 5.05V but anything below that is a bit hit-and-miss.
From Russia with Data
Although I had managed find numerous TDK Lambda NV1 handbooks, datasheets, application-notes and so on, from the UK and US TDK websites, they had no documents describing the really critical bits: does the PSU have built-in across-the-line AC filtering and line-to-ground filtering, and what is the actual maximum (trimmed) output voltage of channels 1 and 3?
As is so often the case when needing such specification details, the information was available from Russia. TDK’s Russian website, to be precise. Even though the “17159-20” handbook is freely available from that site, I always feel a little bit surreptitious getting such information from tertiary manufacturers sites. A hang-over from kremvax days, I suppose.
Thanks to the Russian-sourced data, I can see that the NV1-175 (NV-350TT flavour) has user-adjustable trimming-potentiometers and the nominal 5V channel 1 is formally rated upto (and qualified for) 5.5V before the over-voltage protection cuts-in, here’s a close-up of the trimmers:
Twiddler On the Hoof
Most potentiometers are eg: 10-turn devices, but the suckers on the NV1 are way way way more than that, dozens of turns from bottom setting to top. I initially was turning the adjuster as slightly as possible to avoid overshooting (once you push the NV1 into over-voltage-protection, it’s a bit tricky to get it out again, except by blind adjustment whilst removing/reapplying main power).
Of course, my very delicate touches were making absolutely no difference to the measured voltage – were the pots broken or the Russian document incorrect, or what?
Poking a screwdriver into the guts of a live PSU is pretty scary, not something to take lightly, so big twists on the pots just didn’t seem like a good idea at the time. Eventually, after I plucked up the courage to twist the driver enough to make *some* difference, *any* difference, I managed to get the nominal 5V line to 5.1V (instead of the 4.98V it had been opriginally). However, without the PSU under load, the measured voltage wobbles around quite a lot, it just wouldn’t go stable. Given that I picked the NV1 particularly because it had no “minimum load” requirement, this was a bit disappointing.
After several hours without getting stability, flickering between 5.0V and 5.19V, I decided that I would have to make the tuning adjustment “in-situ”, actually hooked-up to the SPARCstation-10 with everything switched on. Now this is starting to sound very dangerous! If that big cap on the NV1 board blows or fails-short, well…
It still took a while, I had to pretend I had four hands (one for each probe, one for the jewellers screwdriver, and one for the mains plug). Eventually, though I could get a stable 5.1V on the nominal 5V lines and a stable 12.0V on the nominal 12V lines (which had been at 11.97V beforehand).
That should do it! For anyone else trying this: be prepared to take a *lot* of time here, these pots’ screws have some “slew” (changing twist direction does not take effect immediately).
Now it was time to try installing an operating-system, Solaris 2.6 has modest requirements, and works very well on this class of machine, so that is what I chose. In this picture, the external CDROM drive and NV1 are connected, all ready for Solaris installation.. The stuck-on paper envelope is there to keep the fan-air over the CPUs rather than escaping into the room… touch-tests show that it is necessary… The O/S installation went through fine:.
The Moment of Not Telling Too Many Lies
Well, now that we have an O/S and a working system, surely it is time to try running the pair of 180MHz HyperSPARC CPUs that the original PSU could not manage?
It would be exactly that time, except that I have misplaced those darned CPU modules (Where’s Wilma?)!!!
Never mind, this gives me the opportunity to show the SPARCstation-10 doing something rather unusual, something that very, very few other systems of the time could do, and that many modern systems still cannot do: run three CPUs with different base speeds, cache sizes, and different number of levels of cache, all under control of a single operating-system instance: I have another single-CPU 180MHz module, and a dual-CPU 90MHz module. That all adds up to 360MHz, and that earlier dual-90 unit actually consumes more power and dissipates noticeably more heat than the newer die-shrunk 180MHz modules do, so in terms of stressing the new PSU, this configuration will be even *more* of a test. Does the system still boot? It sure does! (video). And repeatably consistently, yay!!!