Repair of a Vintage Simpson 461-2 DMM - Page 1
Forum section: electronics / testgear

author: xrunner
author_rank: Super Contributor
timestamp: February 13, 2015, 06:39:57 pm
content: Yet another project - the repair of this Simpson meter. This unit has red LEDs and is capable of using rechargeable NiCads. The unit came with the original batteries but they are no good. The unit also does not work. When power is applied it draws way too much current (as much as it wants depending on the voltage applied) and the LEDs do not light. Also emitted is the magic smoke - well at least the smell of it, I didn't observe any of the original smoke coming out. Upon inspection I believe the Intersil IC7107 3 1/2 Digit LED Display A/D Converter is bad. I can see a discolored area right in the center of the package and it reeks of the magic smoke smell. I do not observe any other component that looks overheated, and the IC package that supplies/converts additional voltages to the board from the input +5V is working as expected.I went ahead and pulled that guy, and when power is re-applied, the system seems normal and only a few mA is pulled from the supply. The 40 pin IC is now on order, and we'll see what happens next week ...

author: SeanB
author_rank: Super Contributor
timestamp: February 13, 2015, 06:59:09 pm
content: Check the supply rails are correct, I cooked one when the -5V rail did not come up correctly and the chip latched up and cooked. Check that ICL7660 and the tantalum capacitors attached to it that it can deliver -5v and can deliver at least 20mA into a resistive load without dropping below -4V, use a 270R resistor as a test load and check across it for excessive ripple.

author: Smith
author_rank: Frequent Contributor
timestamp: February 13, 2015, 06:59:40 pm
content: These icl series chip fail quite frequently. Most just show strange values (or strange digits) or show non linear behaviour. Havent seen any draw too much current though.A lot of (older) 3,5 - 4,5 digit lcd voltmeter modules use these chips too. Thankfully you can still get new chips after 15-20 years.

author: xrunner
author_rank: Super Contributor
timestamp: February 13, 2015, 08:29:48 pm
content: Quote from: SeanB on February 13, 2015, 06:59:09 pmRoger - thanks.Quote from: Smith on February 13, 2015, 06:59:40 pmYea it's great it's available - getting it from Mouser.I found another problem. Decided to check all the segments of all the display LEDs using a 5V supply and small resistor. Out of all the 7-segment display parts one and only one has a segment that does not light up (the bottom segment). I removed it from the board and it is definitely not working. It would be expected to display a Zero at times so it needs to work. Why just one - who knows, but I can the exact same part off Ebay.Ever watch the Movie "The Money Pit"?Reference part -

author: xrunner
author_rank: Super Contributor
timestamp: February 14, 2015, 03:18:04 pm
content: Few more pics while I'm waiting for the parts.There is a regulator unit on the board that accepts +5 and supplies +12 and -8V. It's the Astec AA4750. What I think happened to this meter was too much voltage was applied to the battery or charger input. The devices that run off of the +5 may have been damaged (such as the ICL7107 I ordered), but I have yet to find any other defective parts other than one of the LEDs. Other parts of the circuit that use the +12 and -8 were saved because the converter keeps supplying the proper 12v and 8V even if the supply is increased too much.These little wire thingies provide a connection to the LED display when the top board is attached to the bottom. The other connections are made with a proper connector near the back. This seems a little dodgy to me.Here is the LED display board with the defective LED removed. Not ordering it yet until I see if this unit is going to be able to be fixed.

author: xrunner
author_rank: Super Contributor
timestamp: February 14, 2015, 08:03:12 pm
content: Oops - another casualty found. MPS3702 on LED board bad. Subbed with a 2N2907 PNP on hand. Again consistent with a possible high voltage on the power supply input feeding to certain components (including this one), which didn't affect the +12V and -8V supplies.The pile of dead bugs grows.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 14, 2015, 08:17:14 pm
content: Is it an idea to replace all of the 7 segment units?The new ones give a lot more light and as they are multiplexed you end up with one bright 7 segment, and 3 lesser?

author: xrunner
author_rank: Super Contributor
timestamp: February 14, 2015, 08:23:05 pm
content: Quote from: JohnnyBerg on February 14, 2015, 08:17:14 pmYea I understand your concern. I found a supplier on Ebay that has the exact same part - looks identical. Probably from old stock. I plan on buying one next week if the repair looks promising after the main IC is replaced.

author: xrunner
author_rank: Super Contributor
timestamp: February 17, 2015, 11:07:01 pm
content: Decided to socket the ADC chip, to enable easier troubleshooting/replacement. Hopefully the chip will show up in today's mail. The postperson is way late - slammed because of the holiday yesterday.

author: xrunner
author_rank: Super Contributor
timestamp: February 18, 2015, 04:14:15 am
content: Good news - the mail arrived.I got the chip and inserted into the socket. I then powered on and ...It works!I did find out I'll need to buy two new LEDs, but that's no big deal. It even shows the correct voltage. It should be reading -12.2 V and you can see the LED is missing two segments. Had to bypass the anode voltage on the missing one with a jumper. This is really looking promising now. I think from what I see all I'll have to do is cal it and then do a cosmetic cleanup.

author: xrunner
author_rank: Super Contributor
timestamp: February 18, 2015, 11:40:40 pm
content: Waiting on parts again, I thought I'd try to clean up the case. I ran into a problem. It looks like it has specks of paint on it. I've tried all these cleaners -AlcoholSimple GreenPaint thinnerSoap and waterOrange degreaserI can't get rid of the specks.Any ideas?

author: lowimpedance
author_rank: Super Contributor
timestamp: February 19, 2015, 12:23:15 am
content: Must be some difficult 'Sh!t' to remove if none of what you tried made any impression at all!!.what about ;WD40, kerosine, mineral turps. Best to try a small spot first if the case is plastic.Cant say if you will have any luck with those either, so maybe just live with the specks.You should be looking at the display not the case anyway.If you do get it off post back the magic liquid that did it.Seems you have a bit of a thing for old multimeters !.You know the HP3435a had a touch hold probe assembly similar to the Fluke 80T-H which is used with the 8010, 12 and 50 series.The 34112a, (the small hole between the V/ohm and COM terminals is for this probe!).If you want to add to your collection of oldies see if you can get a HP3476a/b, (that's one odd looking beast!).

author: robrenz
author_rank: Super Contributor
timestamp: February 19, 2015, 12:41:05 am
content: Quote from: xrunner on February 18, 2015, 11:40:40 pmUse a magic sponge with any of the cleaners above. It may take quite a bit of rubbing and I would be very careful on the printed info as it may take the print off also. You may also see if the individual specks will pop off with a soft plastic scraper.It looks a lot like house fly crap which is fairly hard to get off also.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 19, 2015, 01:08:30 am
content: I've had good luck with "goop" brand hand cleaner, but sometimes it works very slowly. Apply, let set, wait, rub, wait, apply more, wait, rinse off, evaluate, apply more, rub, wait, apply more, and on and on

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 19, 2015, 01:23:54 am
content: Quote from: xrunner on February 18, 2015, 11:40:40 pmCan you scrape any of them with a fingernail ? Alternate idea would be an old toothbrush with a bit of toothpaste. Toothpaste, depending on the brand, is a mild abrasive. Might try the baking soda and peroxide kind.

author: xrunner
author_rank: Super Contributor
timestamp: February 19, 2015, 01:30:28 am
content: Quote from: lowimpedance on February 19, 2015, 12:23:15 amIt's tough - part of the problem is that the surface is not all smooth. Most of it has a molded-in texture that is really making it hard to get to the "stuff". Most of the scrubbing is hitting the plastic while the stuff remains hiding in the crevices.QuoteYea it's fun to restore old stuff. And - this stuff is good especially those HP meters. NOT boat anchors.QuoteAh those little holes! I was wondering about those. I thought some jerk had drilled a little hole in the front panel, until I saw the other HP meter I got off Ebay had the same little hole. Thanks for solving that mystery!Quote from: robrenz on February 19, 2015, 12:41:05 amI've heard of the magic sponge but never got one. Seems now is the time to try it out.Quote from: Excavatoree on February 19, 2015, 01:08:30 amYea that's what I meant by orange degreaser - tried it and no effect.Quote from: cosmicray on February 19, 2015, 01:23:54 amNope, wish I could. They are embedded in the texturing on the case plastic - it's not smooth.QuoteOK good idea. Will try that tomorrow.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 19, 2015, 01:55:15 am
content: Quote from: robrenz on February 19, 2015, 12:41:05 amNow that would never have crossed my mind !.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 19, 2015, 01:25:44 pm
content: Quote from: xrunner on February 19, 2015, 01:30:28 amJust for the record, and it may help someone else, the old fashioned, plain white stuff works better than the "orange" formula. You'll probably find something that works better in this case, but the plain white goop works well for sharpie brand marker on Fluke yellow plastic.

author: xrunner
author_rank: Super Contributor
timestamp: February 20, 2015, 03:09:41 pm
content: Well ... I managed to get most of it off. And what did I use?...Mother's Mag wheel polish.That was the only thing that would make a dent in it. I didn't get it all off but that's all I'm willing to do. So, the cabinet is now cleaned up - still waiting for LED parts.

author: xrunner
author_rank: Super Contributor
timestamp: February 22, 2015, 12:08:33 am
content: Still waiting on parts but I ran into another problem traced to dirty switch contacts. If you need to know how to remove the innards from these types of banked switches for cleaning the trick is shown below.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 22, 2015, 01:52:05 am
content: Thanks. I've got one of those, and I may need to do that.By the way, does yours take some strange battery? I can't figure out what mine is suppose to use. (So I use alligator clips and a power supply)

author: retiredcaps
author_rank: Super Contributor
timestamp: February 22, 2015, 03:39:17 am
content: Quote from: xrunner on February 22, 2015, 12:08:33 amGood repair and restoration. Thanks for the tip on these switches. I will have to remember this thread for the future.

author: xrunner
author_rank: Super Contributor
timestamp: February 22, 2015, 01:40:52 pm
content: Quote from: Excavatoree on February 22, 2015, 01:52:05 amIt came with two NiCad packs, each of which which consisted of two smaller NiCads shrink-wrapped together. Of course they were no good. It will run off of 4 AA batteries but it's not made to hold them as such, unless you shrink-wrapped two together to make on long battery like the original had. I don't plan on ever doing that, just run it off the charger jack, it works just fine that way (assuming it's fixed like mine isn't yet)Quote from: retiredcaps on February 22, 2015, 03:39:17 amThanks. I'm just going to pull out all the switch insides now, and clean them. Hopefully the LEDs will show up early this coming week.

author: xrunner
author_rank: Super Contributor
timestamp: February 22, 2015, 11:38:45 pm
content: And now a plastic piece that holds a brass insert for the rear screw popped off. Glued back on with model cement.

author: xrunner
author_rank: Super Contributor
timestamp: February 23, 2015, 10:28:31 pm
content: The vintage LEDs arrived today. Meter is looking good! I think we're on the downhill side of this project now.

author: macboy
author_rank: Super Contributor
timestamp: February 24, 2015, 12:58:02 am
content: Quote from: Smith on February 13, 2015, 06:59:40 pmOh I think it's been closer to (maybe over) 40 years since those exact chips hit the market. I have a couple around 30 years old.

author: Panchdara
author_rank: Newbie
timestamp: February 24, 2015, 10:20:15 am
content: Well done! When you started you mentioned the movie "The Money Pit".. well, is your new nickname Walter Fielding? (Hope not) (But it was funny watching that turkey fly!)

author: xrunner
author_rank: Super Contributor
timestamp: February 24, 2015, 03:45:32 pm
content: Quote from: Panchdara on February 24, 2015, 10:20:15 amLOL - thanks.OK - it's certified as working now! I also dug out a 7.5V wall wart from my junque box and made up an AC adapter for the thing.All I have to do is put it back together (without anything else breaking) and see what we got.

author: xrunner
author_rank: Super Contributor
timestamp: February 25, 2015, 03:50:19 pm
content: Well it's put back together and it works like a champ. Got the calibration tweaked up and pretty satisfied with that. Parts required were:ICL7107CPLZ Intersil Analog to Digital Converter + socketTwo HP hp 5082-7731 vintage seven segment LEDs2N2907 PNP transistor7.5 V wall wart for external powerSimpson test lead set in transit from Chile (thanks Lightages).First pic checking calSecond pic shows it atop another similar meter in Simpson's line - the 467.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 25, 2015, 10:57:38 pm
content: Doesn't that look great, and still useful.However the last pic is not complete yet............... needs a 'nixie' Simpson (did they ever make such a meter ??!.), and a moving coil meter for completion.I like the oldies too, Well done.

author: xrunner
author_rank: Super Contributor
timestamp: February 26, 2015, 01:37:31 am
content: Quote from: lowimpedance on February 25, 2015, 10:57:38 pmI do believe I've seen an older Simpson model on Ebay with nixies. Now I need to go find one for my next restoration. I'm off to Ebay for a search!QuoteThanks.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 26, 2015, 01:56:47 am
content: Quote from: xrunner on February 26, 2015, 01:37:31 amBe careful. That's how it starts. I thought "I'll fix this one Fluke, then maybe get another from E-bay to fix."Do you want/need another 267 for parts or repair? I've got one I don't think I'll do anything with.

author: ModemHead
author_rank: Frequent Contributor
timestamp: February 26, 2015, 02:03:58 am
content: Nice job, it looks great! Thanks for posting the progress reports. I like old stuff, too.I may have to get some of that mag wheel polish myself. Turns out car care products are quite useful for restoring old electronics. Meguiar's headlight restoration kit works great for DMM LCD lenses.

author: xrunner
author_rank: Super Contributor
timestamp: February 26, 2015, 03:00:36 pm
content: Quote from: Excavatoree on February 26, 2015, 01:56:47 amOh no another onewhat do you want for it?Quote from: ModemHead on February 26, 2015, 02:03:58 amThanks, yea you never know what will work on what. I have all manner of car product in my garage so it was only a matter of time.

author: xrunner
author_rank: Super Contributor
timestamp: March 03, 2015, 04:29:36 pm
content: Update:Just arrived from Chile, courtesy of Lightages. Set of NEW Probe Master test leads for the older Simpson meters (reverse banana plugs). Wow. Many thnaks to Lightages!

author: Excavatoree
author_rank: Frequent Contributor
timestamp: March 03, 2015, 05:13:54 pm
content: Quote from: xrunner on March 03, 2015, 04:29:36 pmDon't the newer Simpson 260 meters (series 7 and seriesuse these? I've heard them described as "Reverse banana." Or is my memory hopeless?

author: xrunner
author_rank: Super Contributor
timestamp: March 03, 2015, 08:14:48 pm
content: Quote from: Excavatoree on March 03, 2015, 05:13:54 pmI don't think so. I think the newer Simpson meters are "normal" banana plugs, from what I see Googling pics. Some bright guy back in the day had the idea that the "pointy" end of the connection should be on the meter, so that if the leads were connected to a high voltage, and also not in the meter, the end of the lead would be safer. Of course it's all changed in the modern era.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: March 03, 2015, 08:31:50 pm
content: Ah, it's the latter case, as I expected. I still consider this one:http://simpson260.com/260-8/simpson_260-8prt.htmto be a "new" one. I'm sure the 8X and 9x types are newer, and they have the "normal" leads. So they changed, then changed back. (series 7 and the "black" series 8 260s have the "reverse" leads) It's all too much to keep up with.

author: Robbdoe1
author_rank: Contributor
timestamp: September 24, 2023, 05:58:12 pm
content: Hello. I’m in the learning process of meter repair and need help from you all. I too have a very nice 461-2 that has similar responses to the original post. I seem to get random numbers on the display. The volts in both AC and DC don’t respond to any input. All the resistance ranges display a 1 when either the leads are shorted or any resistance measured the display starts to show numbers that always count down to -000. I’m doing my tests with no batteries in the unit and running off the AC charger.I’ve checked the basics like F1 and F2. I know very little about this type of logic. Based solely on the original post I jumped straight to ICL7107. According to what I see on the schematic I should have +5V between pin 1 and pin 21 of ICL7107 and I do. This is where I’m completely lost as I can see pins 30, 31 & 32 are Common, Input Hi & Input Low but don’t know how to test them and don’t want to smoke anything if possible. I have a logic probe if this is where I use it? I have used one once and that was 20 odd years ago.Can somebody please point me in the proper direction to continue troubleshooting this meter? Any and all help is greatly appreciated. Thank you in advance for helping me struggle through this.Robb