General Resistance RTD-100 Teardown and repair. - Page 1
Forum section: electronics / general

author: Vgkid
author_rank: Super Contributor
timestamp: October 06, 2018, 04:37:14 pm
content: I have always wanted an rtd calibrator / milliohm box. Well it finally happened , and here is what I got...I will apologize , my pics didn't turn out too well. I can't use my lab(packing stuff up , to move it into the unheated garage) plus my mom is recovering from knee surgery , don't want to risk it.I included a variant image of this unit.

author: Vgkid
author_rank: Super Contributor
timestamp: October 07, 2018, 05:05:25 am
content: For this , the tear down will be first , and a short overview on the theory will be later.**I will add a few more pics as I go through the unit**After seeing the outside of the unit , lets look at where the output terminals should be.We are presented with one gold binding post , most likely a Pomona 3770. The other 3 binding post are missing , they look to have been cut from their wires. The binding post sense leads are connected to the source leads by a gold binding post link( judging from other pictures)The first 3 decades follow the conventional decade resistor layout , except the '1' position on the 10-Ohms range is its lowest setting. The resistor for this represents the difference between 10 Ohms , and the rest of the lower shunted mill-ohm values.The milliohm range represents a large shift in the expected values in a decade resistor. These occur by shunting a resistor , with varying resistors in series. This will give a range that will increment by a desired amount. This will be explained more later.

author: bitseeker
author_rank: Super Contributor
timestamp: October 07, 2018, 05:20:48 am
content: Cool. Following along...

author: mnementh
author_rank: Super Contributor
timestamp: October 07, 2018, 01:58:32 pm
content: Some fuckwit defiled a laboratory-grade resistance box with dikes to harvest $6a few $$ worth of banana jacks...Where is the [Punch him in the DICK!!!] button on my keyboard? I need it RIGHT NOW!!!mnemDon't forget to use silver-bearing solder when you restore; keep it as original as possible.

author: Vgkid
author_rank: Super Contributor
timestamp: October 07, 2018, 06:51:23 pm
content: Unless that other banana jack is able to be cleaned , I will need to grab 4-3770 thats like 45bucks. I can't wait to test it.

author: Kosmic
author_rank: Super Contributor
timestamp: October 07, 2018, 07:09:59 pm
content: Quote from: Vgkid on October 07, 2018, 06:51:23 pmThere's also the Mueller BU-P3770. Supposed to be similar to the Pomona but cheaper. You can find them on arrow for 8$ shipping included.

author: Vgkid
author_rank: Super Contributor
timestamp: October 07, 2018, 09:32:46 pm
content: Quote from: Kosmic on October 07, 2018, 07:09:59 pmI see digikey stocks them , might need to add them to my resistor order.Arrow is a painful site to use , if you don't know part numbers.

author: bitseeker
author_rank: Super Contributor
timestamp: October 07, 2018, 10:10:14 pm
content: Quote from: Vgkid on October 07, 2018, 09:32:46 pmYep, it sure is. But sometimes (not always) they have the best price. The free overnight shipping is nice as well.

author: mnementh
author_rank: Super Contributor
timestamp: October 08, 2018, 03:54:33 pm
content: Crap. I had no idea they were that expensive now.Good single-contact jacks like that were a couple bucks from ECG; I figured that thing was probably coeval with them.mnem*Sigh* I sound just like my grandmother..."Kids are fuckwits. Cars are ugly. Stuff costs more."

author: Kosmic
author_rank: Super Contributor
timestamp: October 08, 2018, 04:18:52 pm
content: Quote from: mnementh on October 08, 2018, 03:54:33 pmCopper is expensive now. Brass binding post are cheaper.

author: Vgkid
author_rank: Super Contributor
timestamp: October 09, 2018, 02:19:54 am
content: Filed a small amount off the end of the binding post , and it looks to be gold plated brass. I will tell more tomorrow. I will also get some better pics , hopefully. taking pics out side.Correct , gold plated brass .