I really must get some sleep - been up a crazy number of hours with the GDS but will leave you all with the write up for day one of the restoration project which is still in its feasibility stage but after being pleasantly surprised by the condition and completeness of the keyboard console I'm pretty sure this one is a starter...
Some of the test gear in my new synth workshop (much has been used in my sound design!)
Yesterday was a bit of a roller coaster ride...
I stripped down the entire IMS8000 host computer to nothing but a large empty metal chassis and managed to greatly improve the appearance of the rear panel with a significant amount of metal polish and gave everything a good clean along with replacing several broken SUBD locking posts and amazingly managed to find an identical fuse holder cap to the one that had smashed from a piece of kit from the same era I had only scrapped last week!
I then scanned all of the S100 cards on both sides for posterity and as a record of the position of all the factory fitted green wire mods and gave everything a visual check including the two drives and the PSU chassis.
The metalwork internally is in very nice condition with the nickel plating still nice and shiny. Everything is present and complete in the system unit (I now need to do the same with the keyboard console this afternoon – UPDATE: it is 100% complete and original).
I fired up the 115V cooling fan – quiet with good bearings. I fired up the 220V spindle motors on the drives – run ok but then noticed the head on the A drive is rather worn.
I then wound up the (linear!) PSU in isolation on a variac after a few mins sitting at 25% and all the rails were good. I need to look into replacing the stud mounted (50,000uF!) caps at some point but fortunately the large PSU chassis is pretty easy to remove.
I decided to slowly reassemble everything but excluding all the custom synth boards.
I then turned my attention to the ADDS Regent 20 serial terminal but very quickly after removing the lid I discovered that some tech had clearly been in there some time before and come to the same conclusion... at some point someone has dropped the terminal and broken the neck pcb and the glass pip clean off the back of the picture tube (CRT = RIP!) – more on this towards the end.
So realizing the original terminal is never likely to run again without either a replacement tube or a donor monitor chassis I set about finding some appropriate cables to attempt to emulate the terminal instead on a PC. At first I thought the GDS used a current loop serial interface but it turns out everything is set to standard RS232 at 9600-8-E-1 (thank heck!)
Since the A drive heads seemed worn I reconfigured the B drive as A and reinstalled it.
After a few more checks I plucked up the courage to slowly fire up the reassembled computer and nothing much seemed to be happening for quite some time and I was starting to get really depressed thinking we have a basket case on our hands until I noticed after some probing around that the floppy controller card was firing a 5V signal at the solid state relay in the PSU that is supposed to enable the 220V floppy drive spindle motors but the motors weren’t starting up despite me knowing they were good. I temporarily wired this over and started the system again (update: I have a new SSR on order [yup – like the console switches and knobs, they still make them!]) – the heads suddenly zeroed themselves after a reset so since I was now using a drive with shiny heads I decided to chance putting a disk in and after a little fiddling with HyperTerm to my amazement the system booted with a GDS prompt!!!
So I decided I’d only do this once before taking the disks to a specialist but this boot (amazingly) was off the really worn disk and so with the OS still running I swapped over to the voice disk and ran a DIR on that too...
So now at the very least I have the OS build vers and disks contents from both disks.
Todays Update: Stoney thinks he’s found copies of the original programs and voices in digital form and hes going to copy them over a sever soon. I have also managed to find a box of still sealed 8” disks and what I’m now hoping to do is boot the system enough to format a new disk. This would give us a decent blank boot disk to image for HxC system. If that was successful then I can do a very similar exercise to what I do to make the virtual disks on the Synergy by hand copying the programs back on to a virtual OS disk image. The sheer beauty of this method is that if it works then I can use the HxC to make a real OS disk – this is what I can now do with the Synergy and can make as many copies of the system disk as I want
The contents of the demo voice disk is fascinating (it is the very update disk detailed in the letter to Klaus from Tom Piggott at Crumar in Jan 1980 with all the paperwork) – it has suddenly become apparent to me that many of the stock Synergy sounds (some of which are brilliant) clearly had been programmed well before the Synergy was released.
There also at least some hope now that the disk contents can be recovered using modern inferred bit transition oversampling techniques should Stoney fail to find any files (the disk is not in good shape at all and is very badly scuffed – I managed to make some utils work but the main VOICE and PERFORM programs are producing disk errors on loading)
But still – this is a lot of progress after only a days (intense!) work.
Needless to say I’m now treating the two disks like gold dust.
Regarding the terminal – I have found a company that can sell me a new direct replacement CRT for the original. Expensive but it would be a great shame not to have an authentic ADDS Terminal.
Furthermore I have found a company who are able and willing to make a backup of the boot PROM on the I/O card – Stoney does not have a copy – if this PROM fails it’s game over so it’s really important I get this done even if I have to drive it there in person as nothing I have will touch an old three rail 2708.
This project is now starting to feel doable and I was extremely excited to witness the system booting. There is, however, a lot to do.
In terms of what is to come – I need to replace a heck of a lot of old axial and jelly bean type tants both of types that are known to be failure prone (and indeed what killed my Synergy in the first place!), replace the very scary 50,000uF stud mounted caps in the linear PSU, image the ROMs, hand reconstruct working system and voice disks from various sources, fit an HxC disk emulator having imaged everything, find a replacement for one of the 8” drives, fit a new CRT to the ADDS terminal and assess its condition which I’ve just sourced, fit a new SSR to the spindle motor control, have a missing metal trim strip fabricated for the front of the keyboard console, have the rusty CPU top panel and trim bead blasted and powder coated, have the faux wood end caps at least fixed up a bit (they look nasty rather than nicely aged), give every pot and panel a really good clean, remove and test all of the DRAM chips etc etc...