View Full Version : DEC GIGI and my first magic smoke escape...

May 4th, 2010, 04:42 AM
Today I acquired a DEC GIGI which I remember hearing about in the 1980s but never spied one first-hand.

I am excited to find a GIGI, firstly since it will be my first DEC terminal and secondly that it has a 20mA current loop interface (I'm hoping it will work with the KL8 interface on a PDP-8/E).

But soon after powering up, about 50 seconds or so, while I was intently scanning the attached VGA screen for signs of life, a loud pop and lots and lots of smoke! :eek: My very first experience of this phenomena - I've been expecting it for a while now as I play with machines like this one which are nearly 30 years old (this GIGI is circa 1981) but it was still an arresting event.



a metalized polyester capacitor has ruptured in the power supply either due to old age, one power up too many or an in-rush of too much fresh-clean-green Tassie electricity.

I'm looking for SETUP and NO SCROLL keytops which I am missing for this unit too - if anyone has any spares please contact me. I think VT100 keytops may be compatible in shape and post size too.

May 4th, 2010, 05:37 AM
Congratulations on your new acquisition, and of course the magic smoke rite of passage ;-)

I have one of these terminals lined up too, just need to arrange to pick it up some time. By the looks of it, I need to start stocking up on those filter caps... how many are there on that PSU board?!

May 4th, 2010, 03:27 PM
... need to start stocking up on those filter caps... how many are there on that PSU board?!

Several, here is the schematic from the Bitsavers manual:



May 4th, 2010, 04:45 PM
Ah, the ole magic smoke. As cosam says, a rite of passage for vintage computer restorers.

Alarming for sure, but unlikely to be terminal (excuse the dreadful pun).


May 11th, 2010, 07:14 AM
My first magic smoke experience was very recently on a Panasonic PanaSync monitor.. except we (my friend and I) are unable to find any signs of damaged capacitors or fuses, etc.. very mysterious!

Congrats on the interesting machine, and good luck getting it running again. :)

May 12th, 2010, 06:47 AM
Did you get anything on that VGA monitor before the PSU went pop? I picked mine up yesterday but AFAICT it's 15KHz with sync on green, so I'm not sure VGA is going to cut it. Mine did come with a RGB monitor with BNC connectors, but I'm missing the cable. I might try the composite output on another monitor I have handy, but I'll need to obtain/make a cable for that too.

BTW, my case is missing the badge. I don't suppose you could stick yours on a scanner so I can see about making a replica?

May 12th, 2010, 04:15 PM
I repaired the PSU with an X2 capacitor and it seems quite happy now; I like the fan in the GIGI as it is nearly silent.

We have tried all the screens I could find but so far nothing displays an image (using RGB or the composite output). A Phillips CM8833-II tries really hard to lock but no luck there either.

Steve: yes will do regarding the scanning the GIGI badge. Does your GIGI have all it's keytops?

May 13th, 2010, 02:14 PM
I guess I lucked out on this one. All the key caps are there and I even got a picture with a makeshift cable between the mono (composite) output and a Commodore 1084S monitor. At start-up you get a bunch of vertical stripes, then it slowly fills the screen with white, grey and finally black before the cursor pops up. The fan isn't all that quiet though, so I'll have a look at that.

Is yours showing any other signs of life? I get a long beep at start-up and there's a short click on each keystroke when it's running. The LEDs above the keyboard change when it gets going too.

May 13th, 2010, 03:14 PM
Sounds like your GIGI is close to functional. Could you send the picture of the makeshift cable please, I have a monitor which is close to a 1084S but it would not lock to the signal.

The documentation explains the meaning of the lights and beeps - the GIGI is a pleasant surprise with the number of tests and self-diagnostics it runs on startup. Once the GIGI has completed the tests (and flashed its lights) just the Online light should be lit.


The click you hear is the key-click (as per VT100s etc) - it can be switched off in SETUP.

For the fan we dropped a small amount of oil into the tiny hole on the outside (at the hub). Also check that the fan is clearing the mainboard - we found that the holes in the base of the case are not big enough to allow the standoffs to always sit down which lifted up the mainboard which then clipped the fan blades.

May 13th, 2010, 04:15 PM
Oh, she's running nicely apart from the noisy fan which, looking at it, probably just wants a drop of oil as you say. The frame of the PSU assembly was a bit bent but that was easily fixed with a bit of brute force ;-)

The cable is just a standard 2xRCA lead with one the connectors chopped off. I stuck the bare conductor in the hole of the BNC connector at the GIGI end and taped the shielding around the outer part. I dare say even a regular TV would work, so if you're not getting a picture there's probably something not quite right with the outgoing signal. If you want any measurements taking to compare against, just say the word.

May 16th, 2010, 11:01 PM
As requested here is a scan of the DEC GIGI medallion:


You might also find useful Ned Batchelder's description of the "digital" logo too:


May 17th, 2010, 12:34 AM
As requested here is a scan of the DEC GIGI medallion:
Thanks! I'm not usually too bothered about cosmetics but my GIGI looks decidedly nondescript without this. I'll see what I can do with this and a decent inkjet.

You might also find useful Ned Batchelder's description of the "digital" logo too:

Cool. I was planning to vectorise the scan, but I may well borrow that postscript logo to use as a starting point.

May 31st, 2010, 12:56 AM
With extensive help from my uber-hardware-guru brother, Kit, who managed to identify the reason we are not seeing a lockable video signal: no sync! - the 7426 on the video output side has a broken gate - so we plan to piggy-back a replacement.


May 31st, 2010, 01:03 AM
Wow, I've been following this thread with great interest since it started, so thanks for sharing all this! :)
New dream computer, check!

May 31st, 2010, 01:03 AM
Nice one. Sounds like it's pretty much running otherwise, so hopefully this is all it needs to fix it.

June 5th, 2010, 01:22 AM

We now think the entire 7426 is fried, since we were missing sync on composite (B&W output) too.

Anyhow we piggybacked a 7408 and 7406 to make a new NAND gate for the composite we have output onto a LCD panel (although somewhat shimmery/wobbly - we're not sure why, whether it is poor cabling or something else).



and finally ReGIS graphics drawing circles using GIGI (VK100) BASIC:


We will look at colour next once we figure out the easiest way to get there since the analogue RGB could be picked off earlier in the output stage.

September 5th, 2011, 01:09 PM
Hi, thanks for your post on the DEC GIGI on this forum - it gave me a heads up for what might happen when I first turned on my new acquisition. I guess luckily the previous owner (from new) didn't turn it on otherwise it might have been scrapped.

Anyway, I need to look for a couple of metal film capacitors. I had examined them before turning the machine on and to be honest I should have realised then that one of them was going to give - the plastic housing was cracked on both of them. Now it's cracked a little more on the 0.22uF one!

Hoping that once replaced it springs back to life again.

Regards, Mark.