Simpson 270 series 4 not working - Page 1
Forum section: electronics / repair

author: TimeBandit
author_rank: Regular Contributor
timestamp: January 18, 2018, 09:12:29 pm
content: This new-to-me meter isn't showing a pulse. Here's what I've done so far:• Replaced the D and 9 Volt batteries.• Checked the fuses.• Use cotton swabs soaked in Deoxit D5 to clean the contact surfaces of the Function switch and the Range switch, though the solder side of the Function switch could use more attention.• Followed the troubleshooting steps in a Sears repair doc, which included shorting the + and Common jacks with a paper clip. No response from the meter.• There's no visual evidence of a burnt resistor.Next I'll start checking the resistors one by one and clean the Function switch more thoroughly. But based on what I'm seeing and the experiences of someone else who weighed in, I'm concerned that it may be the meter movement itself. Thoughts?

author: Gregg
author_rank: Super Contributor
timestamp: January 18, 2018, 11:15:42 pm
content: First, congratulations on your efforts to keep an old workhorse operational.A Google search for “Simpson 270 meter manual” will find several copies of the original manual complete with schematics and operating procedures.The two batteries are just for ohms measurement and somebody may have connected the meter to a voltage source while the meter was set to measure ohms, but this should only keep the ohms part of the meter from working correctly.The 10 amp jack isn’t fused according to the manual and if someone tried to measure mains voltage with the leads plugged into this circuit, it may have hosed the meter movement and other things (look for burned places).Try measuring a 9V battery on the 50V DC scale first and then on the 10V DC scale. If no reading, you may have to look into the meter movement.If the meter was dropped or treated too roughly, the hairspring(s) that are attached to the meter pointer could be twisted and may be able to be set back to the original position with careful manipulation.A check of the meter windings with another ohm meter can tell if the meter movement is blown, this may require removing one wire from the meter.

author: TimeBandit
author_rank: Regular Contributor
timestamp: January 19, 2018, 12:22:30 am
content: Thanks for weighing in. Looks like the meter coil is blown. I checked the resistance between the two meter studs and it came up open. Well, at least I didn't pay much for it...

author: TimeBandit
author_rank: Regular Contributor
timestamp: January 19, 2018, 09:00:56 pm
content: Well, I picked up a 270 series 3 that has a good meter movement. Would it be worth transplanting the series 3 movement to the series 4, assuming they're compatible?

author: floobydust
author_rank: Super Contributor
timestamp: January 19, 2018, 09:49:16 pm
content: It looks like the panel meter is the same 50uA 1,800ohms. But I would check the markings for each scale.It's probably worth it to take the old meter apart and see if you can find the open-circuit, do surgery.Sometimes it's (flux) corrosion on the connections inside or a fine wire fell off.Simpson multimeter schematics, manuals etc. here:http://simpson260.com/downloads/downloads.htm

author: Gregg
author_rank: Super Contributor
timestamp: January 20, 2018, 01:17:50 am
content: If, as floobydust suggests, the good meter movement is marked with the same values; they should be interchangeable except for maybe the meter face markings. The meter faces may possibly be swapped if one is really careful not to bend or tweak the needle or the pivots and the dimensions are the same. The meter may need to be zeroed afterwards. Analog meter movements aren’t very complicated, just delicate.

author: TimeBandit
author_rank: Regular Contributor
timestamp: January 21, 2018, 05:05:54 pm
content: I decided just to keep the second meter, the 270 series 3, intact. It had a few issues, but now it's working fine. Comparing its DC and resistance readings to those of two other known accurate DMMs, the Simpson is a little bit off. I need to recheck the readings to see if they're within the error range. Assuming they aren't, I'd like to calibrate this myself, but from looking at the U.S. Navy and Simpson procedures, I'd need a calibrator and power supply, neither of which I have. Am I correct in assuming there aren't any other ways to execute this myself without these tools?

author: floobydust
author_rank: Super Contributor
timestamp: January 21, 2018, 08:26:08 pm
content: You can do a basic calibration if you can make one full-scale (voltage or current) quantity precisely known, OR have another known accurate meter to compare and dial up to the value needed. It looks like master CAL R32 is done with a 50uA DC current, so you could series-connect two or three meters and dial up 50uA with a potentiometer (and safety series resistor 10k-100k or so) or variable PSU/battery, at least a volt or so.The Army cal manual for the 270 is missing stuff- no mention of the master CAL trimpots R27, R32. DC V says adjustments "none".R32 (my guess 50uA DC full-scale)R27 1mA DC R27 (check 5,000ohms meter-circuit resistance, after setting R32)R22 10A DCR28 ACV 2.5VR31 ACV 250VHave the meter horizontal, adjust the panel meter (face) zero screw and see what you get.I would calibrate R32 and R27, and see how the other functions do.

author: TimeBandit
author_rank: Regular Contributor
timestamp: January 21, 2018, 10:19:44 pm
content: Thanks floobydust. For the full-scale quantity, I could probably benefit from owning a variable PSU anyway, so that might be the way to go. Are these all assumed to be accurate as to the voltage they're putting out, or is there something I should look for when buying one?I found an old thread on the Antique Radio forum where someone confirmed your guess that R32 is 50uA DC full scale. The person also has R27 as 2.5mV.http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=56942