Simpson TDS-3 Dwell/Tach

gunnerb17 · Post by **gunnerb17** » Fri May 15, 2020 5:41 pm

I know this is a long shot---But does anyone have a good circuit board for this tester?The Dwell works perfect but my Tach doesnt.Any help greatly appreciated.Thanks

RonD2 · Post by **RonD2** » Fri May 15, 2020 9:08 pm

Did it ever work while you've owned it? Could just be dirty or misaligned switch contacts (they get abused a lot). What makes you say the board is bad?

Do you have the bad board? What kind of shape is it in? Post photos. I ask because it may be repairable. Depending on condition and what it needs, I may be able to help with troubleshooting and repair. Where are you?

Many common electronic components are still available today. And by chance do you have the manual for it? It usually includes parts descriptions and a schematic diagram. If you don't, might be able to still find one. Take a photo of the data plate.

I have a very similar set to yours only made by Bruno (Model 423) not Simpson. I see your set advertised right now on fleabay for $200. Prices have gone up.

Uncle Sam spent big bucks back in the day sending me to avionics repair schools. A tach circuit isn't that complex. If you can provide more information and a photo or two I'd be glad to offer an opinion.

Post by **wesk** » Sat May 16, 2020 12:02 am

This should help:

Large size file is here: http://willysmjeeps.com/v2/modules/gall ... Wiring.jpg

RICKG · Post by **RICKG** » Sat May 16, 2020 8:33 am

I think I have a parts list for the unit-i'll have to check..

Edit: nope on the parts list.

gunnerb17 · Post by **gunnerb17** » Thu May 21, 2020 6:03 pm

Thanks for fast replies and Iam sorry I dont know how to post picturesI have tech manual which shows circuit board and parts-TM9-4910-700-14&P from June 1981.It seems to be different then the TDS-2.The tester works on Dwell but not on RPM.The data plate is missing but it has two simpson meters.Its in real good condition including the leads.I checked the tach cable connection to circuit board which is OK.Didnt see any broken or bad spots on the board.I have the split sleeve tach clamp.Maybe this will help to give me some repair advice.Thanks again

RonD2 · Post by **RonD2** » Thu May 21, 2020 8:03 pm

First question from my original post --- has the tach meter ever worked since you've owned it?

gunnerb17 · Post by **gunnerb17** » Fri May 22, 2020 7:34 am

RonD2 This is the first time I wanted to use it and it didnt work. Thanks for reply

RonD2 · Post by **RonD2** » Fri May 22, 2020 9:26 am

Just trying to help you troubleshoot it (long distance).

My second question from the original post: What makes you say the board is bad?

gunnerb17 · Post by **gunnerb17** » Fri May 22, 2020 10:18 am

I dont really know about the board . I just thought one or some of the transisters maybe bad?From the circuit diagram it looks like there are two separate circuits one for dwell the other for tach. THANKS

RonD2 · Post by **RonD2** » Fri May 22, 2020 10:38 am

Do the switch knobs operate smoothly and positively between settings? Not loose or gritty? Do all the contacts on the back side look good on visual inspection? Have you cleaned the contacts on the back side of them with electrical contact cleaner spray and a drop or two of lubricant (WD-40 )?

If yes, and still no joy, and a careful visual inspection shows no frayed or loose wires, and there's nothing burnt, arced, bubbled, cracked, bent, or broken --- then I'd agree it's either the circuit board or the meter movement itself. Unless the set was dropped or took a hard hit, these meters are pretty rugged, but have been known to fail. Your TM might include procedure to test it by itself to confirm its condition before starting on the circuit board.

If it comes down to troubleshooting the components on the circuit board, checking them with a schematic diagram and a multi-meter is fairly straight forward. But before I did that I'd want to do an interweb search on the transistor part numbers to make sure they can still be bought. Odds are yes, but warrants a check to be sure.

With some good photos, a schematic diagram, and a multi-meter, I could probably walk you through checking the board for common failures, over the phone, not typing in this forum. Where are you located?

gunnerb17 · Post by **gunnerb17** » Fri May 22, 2020 5:42 pm

Thanks I will look this over much better .Ididnt look at the switches.Iam located in southern Illinois.I will be going back to work tomorrow so will not be able to do much with it.Phone call would work for me.Many Thanks

RonD2 · Post by **RonD2** » Fri May 22, 2020 7:40 pm

Ok, let me know when able. Standing by......

The part numbers for the transistors and diodes on the circuit board are shown on the schematic. I'll run a few of them on the interweb in the mean time to see if anybody has any.

RICKG · Post by **RICKG** » Fri May 22, 2020 8:16 pm

RICKG wrote:I think I have a parts list for the unit-i'll have to check..

Edit: nope on the parts list.

TM9-4910-700-14&P from June 1981, turns out I do have this TM, Found a few years ago on the web and printed out. My machine is a Simpson TDS1. These are really nice tools to have, hope your issues can be resolved.

At a MV meet in Montana a few years back I displayed my tach/dwell, timing light, test lead set and others with my M38.. The "gray steel box" test equipment got more looks than the jeep..

RICKG · Post by **RICKG** » Fri May 22, 2020 8:23 pm

RonD2 wrote:
With some good photos, a schematic diagram, and a multi-meter, I could probably walk you through checking the board for common failures, over the phone, not typing in this forum. Where are you located?

You won't get much better of an offer than that Gun!

Simpson TDS-3 Dwell/Tach

Simpson TDS-3 Dwell/Tach

TDS-3 Dwell Tach

TDS-3 dwell tach

TDS-3 dwell tach