Grass Instruments Polygraph / EEG / Lie Detector Machine Teardown - Page 1
Forum section: electronics / general

author: dexters_lab
author_rank: Unknown
timestamp: October 26, 2015, 09:33:17 pm
content: 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 recordersi 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 properlyit'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?

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 26, 2015, 09:54:14 pm
content: I agree that it looks like more of the same2, but man that is an impressive piece of hardware!

author: Kjelt
author_rank: Super Contributor
timestamp: October 26, 2015, 10:12:42 pm
content: 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.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 27, 2015, 06:35:33 am
content: Quote from: Kjelt on October 26, 2015, 10:12:42 pmThe 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.

author: Mashpriborintorg
author_rank: Regular Contributor
timestamp: October 27, 2015, 06:58:39 am
content: Awesome looking piece of Equipment! What is the teardown item you picked up, by the way ?

author: dexters_lab
author_rank: Unknown
timestamp: October 27, 2015, 09:00:08 am
content: 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!Quote from: Mashpriborintorg on October 27, 2015, 06:58:39 amit's a Teac RD-111T PCM Data Recorder (records 8 channels of data onto tape)

author: Kjelt
author_rank: Super Contributor
timestamp: October 27, 2015, 12:26:57 pm
content: Quote from: dexters_lab on October 27, 2015, 09:00:08 amLogistic issue, first get awsome machine in tha house, second get the SWMBO and fake back complaints.

author: dexters_lab
author_rank: Unknown
timestamp: October 27, 2015, 12:42:39 pm
content: Quote from: Kjelt on October 27, 2015, 12:26:57 pm"of course it will be gone in a couple of days darling, i cant be untruthful to you, it's a lie detector!"

author: Macbeth
author_rank: Super Contributor
timestamp: October 27, 2015, 01:13:08 pm
content: 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

author: dexters_lab
author_rank: Unknown
timestamp: October 27, 2015, 08:10:47 pm
content: Quote from: Macbeth on October 27, 2015, 01:13:08 pmlol, Jeremy Kyle, car crash tv of the highest order

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 28, 2015, 03:51:51 am
content: Those square-looking knobs though...

author: dexters_lab
author_rank: Unknown
timestamp: November 03, 2015, 06:15:56 pm
content: 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.

author: Mashpriborintorg
author_rank: Regular Contributor
timestamp: November 03, 2015, 06:25:51 pm
content: Beware, prices of scrap metal are currently quite low. Maybe you can also retrieve some money by selling duplicate modules and parts on eBay.

author: dexters_lab
author_rank: Unknown
timestamp: November 03, 2015, 07:05:30 pm
content: Quote from: Mashpriborintorg on November 03, 2015, 06:25:51 pmso 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

author: SeanB
author_rank: Super Contributor
timestamp: November 03, 2015, 07:14:27 pm
content: 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.

author: Towger
author_rank: Super Contributor
timestamp: November 03, 2015, 07:16:50 pm
content: I was watching the price dropping. You could rent it out as a B movie prop.So what does the SWMBO think of it?

author: Delta
author_rank: Super Contributor
timestamp: November 03, 2015, 07:34:56 pm
content: 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!

author: dexters_lab
author_rank: Unknown
timestamp: November 03, 2015, 08:37:28 pm
content: Quote from: Towger on November 03, 2015, 07:16:50 pmlol, she has not seen it yet, my storage is about 20km from homeQuote from: SeanB on November 03, 2015, 07:14:27 pmindeed, yea there are quite a few of the multi-turn dialsQuote from: Delta on November 03, 2015, 07:34:56 pmsadly 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 winterit 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!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 04, 2015, 08:17:40 am
content: There must be an analogue synth nut out there who would wet themselves over that thing!

author: krivx
author_rank: Frequent Contributor
timestamp: November 04, 2015, 08:55:11 am
content: Quote from: mikeselectricstuff on November 04, 2015, 08:17:40 amYep, people use Grass gear for music, just not the traditional analogue synth crowd. Dexters_lab, I've PM'd you about this

author: dexters_lab
author_rank: Unknown
timestamp: November 04, 2015, 11:14:09 am
content: Quote from: krivx on November 04, 2015, 08:55:11 ami guess those amplifiers could be used for a few different things

author: SeanB
author_rank: Super Contributor
timestamp: November 04, 2015, 07:13:04 pm
content: Interested in getting some of those multiturn knobs and pots Mark.

author: owiecc
author_rank: Frequent Contributor
timestamp: November 04, 2015, 08:23:10 pm
content: Wow. Wonderfull piece of equipment for something that never actually worked.

author: Towger
author_rank: Super Contributor
timestamp: November 04, 2015, 08:32:11 pm
content: The Yanks appear to believe in polygraphs! Or at least that's the impression given in movies.

author: dexters_lab
author_rank: Unknown
timestamp: November 04, 2015, 10:21:37 pm
content: Quote from: SeanB on November 04, 2015, 07:13:04 pmno worriesi have a growing list of things to put to one side for people

author: AF6LJ
author_rank: Unknown
timestamp: November 04, 2015, 10:28:19 pm
content: Love those knobs.

author: dexters_lab
author_rank: Unknown
timestamp: November 04, 2015, 10:38:14 pm
content: Quote from: owiecc on November 04, 2015, 08:23:10 pmas a lie detector yes, the evidence is tentative... but these would have been used as EEG (Electroencephalography) machines

author: AF6LJ
author_rank: Unknown
timestamp: November 04, 2015, 10:41:28 pm
content: Quote from: owiecc on November 04, 2015, 08:23:10 pmGoes to show that Even Snake Oil can find a home.

author: SeanB
author_rank: Super Contributor
timestamp: November 05, 2015, 05:59:34 pm
content: Quote from: AF6LJ on November 04, 2015, 10:41:28 pmTrue, 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.

author: iampoor
author_rank: Frequent Contributor
timestamp: November 05, 2015, 06:04:10 pm
content: 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

author: dexters_lab
author_rank: Unknown
timestamp: November 05, 2015, 09:59:11 pm
content: Quote from: iampoor on November 05, 2015, 06:04:10 pmi 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

author: dexters_lab
author_rank: Unknown
timestamp: November 15, 2015, 09:41:09 am
content: 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 upAll 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:

author: dexters_lab
author_rank: Unknown
timestamp: November 27, 2015, 03:33:12 pm
content: 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

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 04, 2015, 06:00:27 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2015, 07:18:22 pm
content: 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.

author: dexters_lab
author_rank: Unknown
timestamp: December 04, 2015, 08:27:21 pm
content: Quote from: mikeselectricstuff on December 04, 2015, 06:00:27 pmthats 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...

author: dexters_lab
author_rank: Unknown
timestamp: December 16, 2015, 11:53:17 am
content: 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

author: Kjelt
author_rank: Super Contributor
timestamp: December 16, 2015, 12:03:27 pm
content: Very nice sturdy mechanical switch at the end of the first video, love it

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 16, 2015, 12:08:58 pm
content: Quote from: dexters_lab on December 16, 2015, 11:53:17 amIs the output ok at around 115V? You'd almost think that...

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2015, 12:10:39 pm
content: 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.

author: dexters_lab
author_rank: Unknown
timestamp: December 16, 2015, 12:16:00 pm
content: Quote from: PA0PBZ on December 16, 2015, 12:08:58 pm...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.

author: dexters_lab
author_rank: Unknown
timestamp: December 27, 2015, 08:35:01 am
content: 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 supplyI 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

author: raptor1956
author_rank: Frequent Contributor
timestamp: December 27, 2021, 08:05:12 am
content: 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

author: dexters_lab
author_rank: Unknown
timestamp: December 27, 2021, 09:14:00 am
content: 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