Grass Instruments Polygraph / EEG / Lie Detector Machine Teardown

[dexters_lab]

while i was picking up my latest junk item to teardown i took a quick look at this interesting item, it's a Polygraph machine, well it's actually two of them, with the chart recorders

i was surprised by the build quality, you wont see that from the pictures but there is a stainless frame with aluminium plug-in modules, all the control knobs etc are machined aluminium, it must have been very expensive when it was new, i didn't have time to start poking around properly

it's an unusual item to see, but i am not sure about taking it for teardown, the seller will take a deal on it but it's going to be a load of mostly identical amplifiers, filters and stuff so i dunno. It's way more £ than i would normally do for a teardown... what do people think?

[PA0PBZ]

I agree that it looks like more of the same², but man that is an impressive piece of hardware!

[Kjelt]

It was probably used in a hospital for EEG,s since the number of probes and units exceed normal polygraph usage. Would be interesting to have a look inside to get a date of build.

[Paul Moir]

Would be interesting to have a look inside to get a date of build.

The Canadian patent listed as pending was issued in 1957 to Albert M Grass, so it must be from about that time.
I'll bet it would be entertaining to see what they thought was adequate isolation between HV supplies and electrodes wired into someone back then.  But I can't imagine the entertainment would be worth much money.  Better things to do with it.

[Mashpriborintorg]

Awesome looking piece of Equipment  ! What is the teardown item you picked up, by the way ?

[dexters_lab]

right well i might let it slip then.

Must admit i really dont have the space for it, i need Dave's workshop!

SWMBO would go nuts if it turned up in the kitchen or lounge!

Awesome looking piece of Equipment  ! What is the teardown item you picked up, by the way ?

it's a Teac RD-111T PCM Data Recorder (records 8 channels of data onto tape)

[Kjelt]

SWMBO would go nuts if it turned up in the kitchen or lounge!  

Logistic issue, first get awsome machine in tha house, second get the SWMBO and fake back complaints.

[dexters_lab]

SWMBO would go nuts if it turned up in the kitchen or lounge!  

Logistic issue, first get awsome machine in tha house, second get the SWMBO and fake back complaints.

"of course it will be gone in a couple of days darling, i cant be untruthful to you, it's a lie detector!" 

[Macbeth]

Just tell her she doesn't have to drag you on to The Jeremy Kyle Show now! Of course this won't help with the paternity testing so you may still have to endure the baying unemployed chavs in the audience for that 

[dexters_lab]

Just tell her she doesn't have to drag you on to The Jeremy Kyle Show now! Of course this won't help with the paternity testing so you may still have to endure the baying unemployed chavs in the audience for that 

lol, Jeremy Kyle, car crash tv of the highest order

[crispy_tofu]

Those square-looking knobs though... 

[dexters_lab]

well i managed to pick this item up for a reasonable price so we have a couple of polygraph & EEG machines to take apart. I wasn't that interested in it but the price made it worthwhile or at least it's a 'free' teardown that shouldn't cost me anything once i have chopped in the metal.

[Mashpriborintorg]

Beware, prices of scrap metal are currently quite low. Maybe you can also retrieve some money by selling  duplicate modules and parts on eBay.

[dexters_lab]

Beware, prices of scrap metal are currently quite low. Maybe you can also retrieve some money by selling  duplicate modules and parts on eBay.

so long as it covers most of my costs i'll be happy... plus thankfully i sell my metal to a specialist company that makes alloys and not to a scrap metal dealer/middleman

[SeanB]

Multiturn dials and the 10 turn pots behind are worth a bit if you sell them. You should have some nice precision opamps there as well, and they likely will all be socketed as well. At least the ones I took apart were, still have the Tek scope out of one that i must recap and turn into a component curve tracer, though the other one with the Tek storage scope in it is likely dead, though the tube might still be usable.

Should pull it off the top shelf and take a few pics of it sometime.

[Towger]

I was watching the price dropping. You could rent it out as a B movie prop.
So what does the SWMBO think of it?

[Delta]

Dex, that is an EXTREMELY cool piece of vintage machinery!  Far too good to be chopped up for scrap!

I'd even buy it off you if the logistics were possible.

You may well find that producers of TV programmes and films set in the 60s & 70s would be interested in it as a prop.

Please don't scrap it!

[dexters_lab]

I was watching the price dropping. You could rent it out as a B movie prop.
So what does the SWMBO think of it?

lol, she has not seen it yet, my storage is about 20km from home

Multiturn dials and the 10 turn pots behind are worth a bit if you sell them. You should have some nice precision opamps there as well, and they likely will all be socketed as well. At least the ones I took apart were,

indeed, yea there are quite a few of the multi-turn dials

Dex, that is an EXTREMELY cool piece of vintage machinery!  Far too good to be chopped up for scrap!

I'd even buy it off you if the logistics were possible.

You may well find that producers of TV programmes and films set in the 60s & 70s would be interested in it as a prop.

Please don't scrap it!

sadly i dont have the room to keep it! In fact it needs to be gone within a couple of weeks as i will be parking up our classic toyota in my container for the winter

it would have been scrapped if i had not bought it, at least this way we can look inside and salvage those beautiful control knobs and other goodies!

[mikeselectricstuff]

There must be an analogue synth nut out there who would wet themselves over that thing!

[krivx]

There must be an analogue synth nut out there who would wet themselves over that thing!

Yep, people use Grass gear for music, just not the traditional analogue synth crowd. Dexters_lab, I've PM'd you about this 

[dexters_lab]

There must be an analogue synth nut out there who would wet themselves over that thing!

Yep, people use Grass gear for music, just not the traditional analogue synth crowd. Dexters_lab, I've PM'd you about this 

i guess those amplifiers could be used for a few different things

[SeanB]

Interested in getting some of those multiturn knobs and pots Mark.

[owiecc]

Wow. Wonderfull piece of equipment for something that never actually worked.

[Towger]

The Yanks appear to believe in polygraphs! Or at least that's the impression given in movies.

[dexters_lab]

Interested in getting some of those multiturn knobs and pots Mark.

no worries i have a growing list of things to put to one side for people

[AF6LJ]

Love those knobs.

[dexters_lab]

Wow. Wonderfull piece of equipment for something that never actually worked.

as a lie detector yes, the evidence is tentative... but these would have been used as EEG (Electroencephalography) machines

[AF6LJ]

Wow. Wonderfull piece of equipment for something that never actually worked.

Goes to show that Even Snake Oil can find a home.

[SeanB]

Wow. Wonderfull piece of equipment for something that never actually worked.

Goes to show that Even Snake Oil can find a home.

True, I have a Bioptron light that I picked up on auction for under $30, and fixed it after a quick google at the stock faults.  Used a PCB transformer from an old industrial control as donor part, so the fix was for free. Now it is a very large white clothes rack.

Stock fault was a burnt out transformer, burnt out because they draw too much current from it, so that they can make a universal input that covers 90-250VAC. The transformer supplies a 12V rail to the SMPS chip, so to do so they have a little TO92 package darlington that has to drop 30V with 220VAC mains, and the current draw from the SMPS controller and the PIC display driver is more than the transformer is rated for, so the internal thermal fuse goes open. Replacement is a 15VAC unit so the current is higher, and the transistor does not cook the board black.

[iampoor]

Havent watched the teardown yet, but the Grass Instruments Polygraph gear I have taken apart was loaded with Grayhill rotary switches. Still worth a good amount

[dexters_lab]

Havent watched the teardown yet, but the Grass Instruments Polygraph gear I have taken apart was loaded with Grayhill rotary switches. Still worth a good amount

i was talking with a friend of mine today and he mentioned the switches, he restores old vintage radios, so i will be saving at least a box full of them

[dexters_lab]

well so far the 7D polygraph and the separate chart recorder are gone leaving me with the 78D polygraph which i have fixed up, plugging things back in and re-assembling using screws and other items from the other polygraph making this machine more complete. I also found the input patch cables. So eventually once i have checked the power supplies i do intend to power this up

All the control knobs from the dismantled polygraph are available to buy if anyone wants them for their own projects:
https://www.eevblog.com/forum/buysellwanted/(fs)-vintage-1970s-aluminium-control-knobs/

I found there are some interesting things inside the modules, it is more than just pretty knobs and dials so I will be opening up some of the modules to take a closer look inside on the next video, certainly the mechanics of the chart pens is quite interesting too.

Have a video looking around the 78D:

[dexters_lab]

i finally got around to take apart of some the guts of this on camera... first off we have one of the DC driver amps and a polygraph integrator

[mikeselectricstuff]

I x-rayed that hybrid - not too clear - I think the resin isn't very x-ray transparent, or maybe there's some shielding - couldn't get anything at all on a side-on view.
Attatched are the best I could get - looks like a single PCB but some parts look like they overlap - could be on both sides or place over each other.

[SeanB]

Potted cordwood board there, and all discrete components as well. You can see the thermally bonded input pair there on the right , and probably X ray opaque because they used an alumina powder filled resin to cast it.

[dexters_lab]

I x-rayed that hybrid - not too clear - I think the resin isn't very x-ray transparent, or maybe there's some shielding - couldn't get anything at all on a side-on view.
Attatched are the best I could get - looks like a single PCB but some parts look like they overlap - could be on both sides or place over each other.

thats very very cool, thanks for taking the time to do this Mike!

when you first look at it everything seems a mess but then you start to think and see... ahh thats a resistor there, TO-18 here, film capacitor there...

[dexters_lab]

yesterday i went over to my container to have a play with the remaining polygraph, took my variac with me so i could power it up.

I turned everything i could off but left the main power switch on and slowly raised the voltage on the variac watching the voltage on the 12v DC test points, the output voltage is stable as the input voltage came up and the mains input current is low (like 20mA or so)

Unfortunately though the output voltage was way above +/- 12V long before i reached full 240v line voltage and at somewhere around 180v input something gives up and it pegs out my variac and trips the breaker built into the main polygraph power switch.

The PSU is a Grass RPS8-16A, it's basically a linear supply with +/- 12v DC regulated output and 12v AC unregulated output. Rated for a total of about 360 watts (input is 230v, indicated 1.5A max) dated 1978.

The DC output is unfused and feeds to the Pen Driver Amps/pre-amp distribution board, there is also a feed off that output as a 1A fused output for 'auxiliary power', the AC output is fused at 1A for the chart recorder paper drive.

The power comes in from the mains plug to the power control module in the rack, through a main power switch and down to the power supply.

I pulled the supply out and have it here on the bench to see if we can figure out whats up with it, powering the supply up on its own does exactly the same here so i think the fault lies in the power supply.

There is a large mains transformer with two secondary windings, the smaller one  to the otuput for the chart recorder, the other is centre tapped and obviously the main feed, this feeds into a bridge rectifier & two big smoothing caps for the + and - rails and onto a regulator board. Significant components on here are a Motorola MC1469 abd MC1463 positive and negative voltage regulators, two 2N6401 SCRs and two 2N5685 transistors mounted on the heatsink.

I noticed one of the 2N6401s goes nuclear hot when it 'trips' so wonder if these are for over voltage clamping?

So its over volting on the outputs. I might repost this in the repair section but if anyone has any thoughts on where to start?

Pics attached

[Kjelt]

Very nice sturdy mechanical switch at the end of the first video, love it 

[PA0PBZ]

So its over volting on the outputs. I might repost this in the repair section but if anyone has any thoughts on where to start?

Is the output ok at around 115V? You'd almost think that...

[SeanB]

My bet is one of the pass transistors is shorted CE on that big heatsink, or one of the 2 TO66 driver transistors, though my bets are on the power devices. Easy to check without desoldering, just check between case and the 2 leads with DMM set to diode mode. Short shows dead, something else says might still be working.

At least the crowbar SCR still works, and the fuse as well..... I have a wall decoration where that did not work, and applied the unregulated 16V rail to a whole computer full of TTL, and suprisingly all survived except a single 5403 30V open collector hex inverter, which blew up at 16V.

[dexters_lab]

Is the output ok at around 115V? You'd almost think that...

...the voltage selection is wrong?

no, there is no actual 115/230v selector, but the primary is centre tapped and connected together. You can see them in the pic, pale blue and white wires looping around in the clear PVC where the primary (purple & black from the power connector) input runs through the chassis to the transformer.

[dexters_lab]

ok, i got the power supply fixed up... all the other components checked out ok leaving me with the two low power voltage regs as suspects, looking through the datasheets for these MC1469 and MC1463, it had examples of using them in dual rail +/- config where the positive regulator tracks off the negative which looks like the setup they have in this supply

I found one of them NOS on ebay for £10 so dropped that in and we're all good (Y)

will make one final video on this polygraph in the new year where i'll power the whole thing up and show how all the chart pens work

[raptor1956]

I realize this is kind of a necro thread, but I came across a video that posters to this thread might find interesting.  Near the beginning of this YT video by some Urbex explorers of an abandoned asylum is a very elaborate Grass Model 7 setup, probably being used as an EEG.  Later on, as they explore other parts there's a lab with a 465 oscope.  Really interesting and somewhat depressing video.




Brian

[dexters_lab]

Interesting, it's been a while since i had the polygraph but interesting to see one again.

i sold mine to a couple of students in Nottingham