SGI: Hardware

robespierre wrote: that's a surprising amount of garbage on the console, I usually only see one or two chars of noise before it settles down on a sun 3/80 or 4/25. I never used the twin tower on serial though.

Solved it. My IRIS console cable has the hardware handshake lines wired, but PUTTY wasn't set to use flow control. I disassembled a good bit of the IP7 PROM many years ago, and I remember that the very first UART output used different routines than the rest. I've long retried the PC that ran the IDA software so I can't look at these listings right now, but I guess that's what bit me here.

The panel with the hex display and the mode switches is now connected, so DIAG is enabled. Now I get :

That's more like it

PS: this thing is 25+ years old, and unlike an Indigo it doesn't hang on an empty battery. Who knows, maybe it still works

Next up, I loaded all boards of the 4D/70, measuring the power consumption (from the wall) each time a board was added.

With all boards installed, power consumption hovers around 400W @ 230VAC. Which means a little over 300W (from the wall) goes to the 5V rail, worst case scenario. Assuming 80% PSU efficiency, some 250W (50A) is a more realistic number. In either case, it is well below my 150A budget The PSU does not make any nasty noises like the original LH Research PSU did.

This is what it looks like right now:

Don't worry about the pixel faults on the screen, it's the LCD which is faulty.

Something else I didn't expect: airflow is top-down, like an Onyx2 deskside. The exhaust is at the bottom of the sides of the main tower. So my plan to install a thermal kill switch above the card cage will have to be re-thought.

I'm quite happy with my progress so far. I've solved two of the problems of this system: a faulty PSU and a faulty blower. I will still have to deal with a sick GM1 board and the system disk doesn't spin up.

Now that I've established that (1) the original PSU was faulty, and (2) the Power-One PSU can handle the system, I'll redo the wiring harness to the PSU properly and drill some holes in the chassis to mount the PSU.

Oh wow, thanks for the details and the great pics! Really having a fab time following your progress with this.

the thermal switches on top of the card cage will still trip if the blowers fail. whether that's fast enough is another question.
the other problems you're having: those old Wren drives really suffer from stiction, try all the old methods like putting them in the freezer and tapping them on the side with a screwdriver handle. The GM1 failure could be one of the sockets: those LGA sockets kind of suck and can get misaligned. Fortunately there's a debug port right on the GM1.

It would be great to maybe host a site providing a video / content rich experience demonstrating each of these systems. From hardware , to booting and running demos

There was a chap who was uploading some great videos on youtube but they seem to have dried up in recent years.. I'd be amazed if he wasn't a user on here? Username on youtube is jpkiwigeek and an example of one of his videos is here:

Ryan Fox wrote: It would be great to maybe host a site providing a video / content rich experience demonstrating each of these systems. From hardware , to booting and running demos

We'll see, maybe once it's back up and running. I also want to build my own site for my collection so I don't want to scatter all my content all over the web either, because I will have nothing left.

Back on topic: the system as I got it had an 8MHz IP4, but I still had a spare 12MHz IP4. Thought I'd give that a spin. Now, I've wondered whether the realtime clock of these things is powered by a small nuke, because the original clock still works in all of my Power Series, unlike just about every other SGI I own. But in this particular IP4 it was dead.

This is what I'm talking about:


Underneath that Sony CXK5816PN-15L static RAM (which holds PROM variables), a Dallas is hiding. It's a DS1216B (this photo is leeched from the 'net):


Basically this clock sits in a RAM socket and turns the RAM chip into NVRAM. Now, when it's dead, you have to key in all PROM variables every time the system powers on which is a major pain in the behind. You can still buy these things from Farnell while supplies last (they have 13 as we speak), but at nearly €50 a piece Should I buy one for my 4D/70, 4D/440, 4D/380 and Crimson, and maybe a spare for good measure? Nah, didn't think so either. Time to bring in the Dremel

I'm not a stranger to this job, but I like to know where to start grinding away. Sometimes the datasheets give you a clue where the Vbat wires must be hiding, sometimes you can find a photo on the internet. Not for a DS126, though.

Luckily, the wife of my colleague works in the Xray department of the local hospital

Which finally answers my questions about the longevity of these things ... not a nuke, but two batteries.

PS: since I had the opportunity, I had the Dallas chips of an Indy, Indigo2, O2/Octane and O200/O2K X-rayed as well. That will be the subject of another post.

jan jaap wrote: PS: since I had the opportunity, I had the Dallas chips of an Indy, Indigo2, O2/Octane and O200/O2K X-rayed as well. That will be the subject of another post.

Nice, looking forward to that. Anything which helps our understanding of these things has got to be a good thing!

xray, haha nice
if anyone is thorough then you

Do you know what else uses the Mighty Mite?

Hint: It's big and orange:

Yup, that is my DECSYSTEM 2020

The connector layout is a little different, I suppose they were made to customer specs.

ah.. the joys of fixing switching power supplies.

I just repaired four MM700 Mighty Mites this weekend. All filter caps on the main 5v supply
read <100uF on a capacitance meter when they should have been 19000. They are very old units, a little
older than the one in the KS10. It is also common for the high voltage caps to fail. The first thing
I would check with a dead switcher are the caps. An ESR meter is extremely handy for doing this in circuit.

All four squeel at different current levels on an active load, but they quiet down at >10A. You can see the
noise level on the main output vary as you apply load.

The squeel seems to be coming from the step down transformer. I'm guessing resonance between the sheets
in the core. You can get the level to vary applying pressure to the transformer core.

Schematics are pretty much impossible to find. I spotted a manual that Tucker had listed on eBay, and that
will be scanned and up on bitsavers when it comes in. If you dig around, people have identified the pinouts
on the DB connector, but the information isn't in a single place.