View Full Version : I now have an Analog Computer - EAI PACE TR-10

November 16th, 2014, 02:25 AM
Well after bidding a ridiculous amount on a PACE EAI TR-10 computer on E-Bay while on holiday in Spain, I have now returned and collected it from its owner. Pictures from E-Bay attached....


November 16th, 2014, 02:33 AM
OK well its time to power it on. I removed the PSU and ran it on a VARIAC for 30 minutes to re-form the caps. Its only low voltage so this should be OK. Checked PSU rails on my scope and only a couple of Millivolts of ripple. Ramped it up to full voltage and installed in the machine. Powered the whole thing on and there were no sparks or bangs so that sounds good.

I patched all the op-amps to have unity gain but sadly most of them just flip off to infinity so I am going to have to start de-bugging them. There is a TR-20 Maintenance Manual on the web so I downloaded that. It looks like the circuits for the Amplifiers are almost the same as those for the TR-10. Just the TR-20 has the input resistors on the amplifier boards, where with mine you are supposed to have separate ones which go in-line with the leads....


Actually the jumper plugs seem to have some kind of think white powder on them,. Not sure if this has leached from the plastic, any one any thoughts on what it is?

November 16th, 2014, 02:38 AM
I now have a way to work on the cards outside the rack. Detached then end socket from the back of the rack and turned it through 180 degrees, about the vertical axis. I can now plug a card in the back and get the scope onto the card. Trouble as they are DC coupled its going to be fun debugging them....


November 16th, 2014, 04:13 AM
this is crazy cool, dave.

November 16th, 2014, 08:20 AM
That looks awesome. Sure you'll have it running in no time :)

November 16th, 2014, 10:24 AM
Well some of it runs now! But I think getting it all running will be fun... Things I think should work don't, and things I think shouldn't work do. So the PSU and Reference Voltage Generator work fine, but the Reset/Hold/Run switch was totally gunged up. I had to prize it apart and clean the gunge out. I know its switching relays but there is a snubber network on the back to prevent the bigger spikes.. I was a bit worried about the Meter but it seems to work reasonably well.

What I am missing are some resistor plugs to go on the inputs of the amplifiers but I think I will replace some of the blank panels with resistor panels. Sadly no time to play tonight, got to finish a talk for some students tomorrow....

November 16th, 2014, 11:01 AM
Dave, is that gray thing in the middle of the photo a mechanical chopper relay? Haven't seen one of those since the 1960s.

November 16th, 2014, 11:18 AM

Yes both the TR-10 and TR-20 use mechanical chopper relays to stabilise the op-amps. They are driven by 6.3V AC from the mains transformer so chop at 50 or 60hz depending on the country you are in. I think the high speed integrator blocks in the TR-20 also use the same relays to switch the integrator capacitors when running repetitive mode.


November 26th, 2014, 08:51 AM
OK Great Progress today.

Simple things first, went to a local Ham Rally and managed to buy a plug to fit the mains socket, so I can now connect it to the power without using a bodge.

Next , as I said above on testing the Amplifier circuits seem OK but the choppers are not chopping. They are in a B9A valve socket so also bought some B9A bases at a rally....

Next I added a couple of 4mm wander plugs on the back panel and tapped into the 6.3V AC that drives chopper relays.

Then I built a box with a B9A on the top and some wander plugs so I get the AC to a "Relay Under Test".

The relays have a horseshoe type electro-magnet at the top, and a finger that wobbles to work the switch. On the faulty switches it looks like the magnets had corroded and there was "rust" stopping it from operating. Cleaned out the gunge and they all work again.




November 26th, 2014, 10:58 AM
Wow - fantastic work! Looking forward to seeing more progress!

November 26th, 2014, 01:31 PM
The RCS/RI people, just south of Boston, have the same machine.

The Rhode Island Computer Museum has your machine's big brother.

November 26th, 2014, 02:31 PM
Thanks for those, I knew Rhode Island Computer Museum had the 580, but I didn't even know that RCS existed. Their TR10 actually looks rather sad with the missing modules or blanking plates. I wonder if the have a service manual?

I do hope to come to the east coast this year and visit the Rhode Island Computer Museum and MARCH. Not sure if I have time for RCS/RI as well...

November 27th, 2014, 04:23 AM
We have a few EAI experts at MARCH and I think the same model computer, on display, as yours. .. or the 20? EAI is from the state of NJ in USA.

Do you have all of the necessary hardware manuals?

I personally have never worked on the MARCH EAI machines but I seem to remember they're complete.

November 27th, 2014, 01:54 PM
I have the tr-20 manual as a PDF, its 95% the same as the 10, but it would be nice to have the real ones. I have a book of application notes which I plan to scan. I also found a US Navy service book for a very similar amp which I guess might have been used in gunnery computers. That uses the same chopper, and has adjustment instructions in for that.

My next move is to replace one of the blanking plates with a panel with 10K and 100K resistors as I don't have any of the 4mm plug & socket with series resistor in ...

December 12th, 2014, 01:32 AM
I scanned the operators manual that came with the TR-10 and its now at Bitsavers in the EAI TR-10 folder.

December 12th, 2014, 01:39 PM
More progress. Now have an extender card made from aTandy/Radio Shack Proto card, an edge connector I got from E-Bay and a kitchen chopping board from our local super market. Sorry about the soldering.21786

January 18th, 2015, 02:17 PM
Well as I have my PC Scope back I can try a few "Programs" and display the output on the scope. I have now tried several "Programs". So first use the two new Pots to add voltages. Plug the system so the +10v Reference goes to the top of the calibrated pots and the wiper goes to one of the amplifiers. So the input can be read off the pot. Here is the wiring:-


Here are the pots set to 5 and 3...


Here is the output. It should be "8" but the reference voltages are a bit low.


Also note its "-8" as the adder inverts.

January 31st, 2015, 03:04 PM
Ok I now have the pen plotter connected. Photos of a couple of plots are in my blog here:-


A video is on YouTube