Sinclair PDM 35 DMM - Page 1
Forum section: electronics / general

author: reagle
author_rank: Unknown
timestamp: June 30, 2012, 10:14:18 pm
content: Just wanted to brag- went to a Hamfest locally and stumbled on this gem- a 1970s vintage Sinclair PDM 35 multimeter! The design shared enclosure with their calculator seriesTeardown is coming up

author: Zad
author_rank: Super Contributor
timestamp: June 30, 2012, 11:28:11 pm
content: Sinclair are (despite their horrible web site) still going and making test gear. They changed their name via mergers and acquisitions a few years back to Thurlby Thandar Instrument (TTI). The people who made the current probe that Dave reviewed a few days back.http://www.tti-test.com/

author: IanB
author_rank: Super Contributor
timestamp: June 30, 2012, 11:32:11 pm
content: What are the headline specs on this device?I remember the time when Sinclair was actively developing and selling devices like that, but I didn't have the money to buy them so I could only drool over the magazine adverts.

author: reagle
author_rank: Unknown
timestamp: July 01, 2012, 04:01:56 am
content: I grew up with a Sinclair ZX Spectrum clone, so things designed by his company will always have a special place for meYet to power it up- it looks full of discrete components and needs a bit of cleanup first. User manual has a schematic in it- that will be handySpecs:Features: 3.5 digit resolution,10M ohm input impedanceDC Volts: mV to 1000V 1%AC volts 1V to 500V 1%DC Current 1nA to 100mA 1%resistance 1 ohm to 10M ohm 1.5%-2.5%

author: reagle
author_rank: Unknown
timestamp: July 01, 2012, 04:50:14 am
content: Well, what do you know- it even works. Missing one segment on all digits, but otherwise reads the voltage as well as my Fluke 8842!

author: SeanB
author_rank: Super Contributor
timestamp: July 01, 2012, 06:09:48 am
content: One dry joint to fix then.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 01, 2012, 09:41:26 am
content: QuoteSinclair's test gear department became Thandar (Agilent style!) when Sinclair went into consumer stuff and computers. They merged with Thurlby, who had been around a while even then and were a bit higher end than Thandar.I wonder if there are any ex-Sinclair people left there today.

author: T4P
author_rank: Super Contributor
timestamp: July 01, 2012, 10:29:33 am
content: It's a lot like HP, don't you think so?

author: reagle
author_rank: Unknown
timestamp: July 04, 2012, 12:16:02 am
content: A few pictures!It appears all missing segments are driven by one pin on the AY (Display driver) chip, so I am not convinced that is fixable. I do see the pin wiggle, but it appears to not be driven high, only weekly pulled, unlike other segments. Going to have to unsolder the tabs to flip the board around for a better look

author: reagle
author_rank: Unknown
timestamp: July 06, 2012, 03:45:52 am
content: And here is the teardown and a bunch more pictures:http://kuzyatech.com/sinclair-pdm35-multimeter-teardownI posted user manual and schematic as well for those interested.Try as I might I was not able to get the missing segments to work reliably- everything is connected correctly, and checks out from the driver to the display pins. Touched up all the relevant solder joints just in case, but to no avail. It almost looks like the actual bond inside the display module is flaky and works some times but not others. Oh well.Overall I am rather dissapointed in the build quality of the unit- I had higher opinion of Sinclair brand, but I guess I never actually owned their products, just clones!

author: amspire
author_rank: Super Contributor
timestamp: July 06, 2012, 04:28:05 am
content: Quote from: reagle on July 06, 2012, 03:45:52 amQuality was never a strong point of Sinclair products, and this was available as a kit, so who knows who assembled it. What Sinclair did was to provide instruments, calculators and computers at a fraction of the price of most of the alternatives at the time. He was a genius at wringing every possible bit of performance out of cheap parts. If you look at computers like the original ZX80, he managed to use the dynamic memory refresh cycle of the z80 processor to drive the video display output using remarkable few extra parts. At the time it was released, this meter was something like 33 pounds, and to get a 3 1/2 digit DVM elsewhere at the time probably costed well over 100 pounds.Who today can implement a computer system with a basic interpreter operating system, bios, a software driven PAL video display, a software driven cassette input/ output and a software driven sound output in 4Kbytes of ROM and a processor running at under 4MHz?The quality of his plastic cases was very basic, and he never minded adding mods to production PCB's to get the product out the door. In my Sinclair Scientific Calculator, which I purchased as a kit, the PCB had connections to a pair of LCD segments swapped, so I had to cut tracks and swap the connections back.The company is still going - sort of. It's latest idea is the wacky and scary X-1 pedal/electric vehicle, scheduled for release in "July 2011".http://www.sinclairzx.com/spec-x-1.htmlRichard.

author: reagle
author_rank: Unknown
timestamp: July 07, 2012, 04:03:14 am
content: Just went through the list of their products on the about page- I never knew they made so many different things!

author: Deodand2014
author_rank: Regular Contributor
timestamp: November 10, 2024, 09:11:45 am
content: Forgive the necroposting, but someone has just posted a repair video for a Sinclair PDM35 DMM to YouTube and I'd rather not start a new topic to cover this.

author: iMo
author_rank: Super Contributor
timestamp: November 10, 2024, 11:01:45 am
content: Nice meter, indeed, the display is prepared for 9 digits alreadyWould require a different repair approach, it seems..