ESI DB877 2nd hand to repair - Page 1
Forum section: electronics / repair

author: sarel.wagner
author_rank: Regular Contributor
timestamp: July 28, 2017, 10:24:51 am
content: So I managed to pick this up used and abused. It has a few problemssomeone badly abused it. The 1ohm range, 10ohm range and 10k ohm rage are the worst.20kohm range has one open circuit 20k wire wound at position 8. The 10 ohm range has the second resistor overheated and indicating 19.789ohm, first 10 ohm is spot on.The 1ohm rage has a few problems, 4 to be exact. 2 of them were really fried, pos 1 reads 1.914 and second one on pos 4 reads 19.784 ohm.So now searching for the following precision wire wound resistors with low tempco (not easy to locate secondhand):20.0k ohm4 of 0.2 ohm2 of 2.0 ohmAny help or advice appreciated. I would like to restore this to close to factory specs. All measurements were very repeatable in 4 wire mode.Regards and thank you.

author: ivi_yak
author_rank: Regular Contributor
timestamp: July 29, 2017, 08:55:17 pm
content: hi, Did you try washing resistor module into ultrasonic machine with Isopropyl alcohol? It will helps

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2017, 12:34:22 pm
content: How accurate do you want them to be, you can order Vishay film resistors from RS with 0.01% that will work there, or you can contact Edward Pettis on the forum and he will be able to wind you some resistors to an exact value and probably a better tempco than the original ones.Where did you pick them up, I got my selection of lesser ones at the local scrapyard with abused resistors, and ordered some 1% film units as repair parts.

author: alm
author_rank: Super Contributor
timestamp: July 30, 2017, 02:28:58 pm
content: Before shelling out $$$ for replacement resistors, and might be helpful to temporarily install some jellybean 0.1% or 1% resistors to make sure the contacts are good. If it was overloaded at some point, I could also see the contacts being damaged.Based on the specifications, I would suggest the following minimum specifications for the resistors:20 kOhm accuracy < 0.02% power >= 0.5 W tempco < 5ppm2 Ohm accuracy < 0.1% power >= 0.5 W tempco < 20 ppm0.2 Ohm accuracy < 0.5% power > 0.25 W tempco < 60 ppmA possible source if you could find it cheaply would be a Dekapot which includes some of those ranges. I would expect the Dekapots to use very similar, if not identical, resistors.

author: sarel.wagner
author_rank: Regular Contributor
timestamp: July 30, 2017, 05:12:54 pm
content: Thank you all Guys.I did start stripping this down to clean up and repair. I do not think it is worth completely disassembling the 2 stacks to individual stacks. The lower resistance stack that was badly overloaded was cleaned in the ultrasonic. Looking much better now. Inspected all those switches and they do not seem to be damaged.The 0 resistance is measuring only 0.022 ohm. This looks better than specs at 40 milliohm. The 1ohm range use 2 resistors, 0.0992ohm at 60ppm/mW and the other 5 PWWs at 0.1992ohm. The 10hm range use 0.9992ohm at 20ppm/mW and the other 5 PWWs at 1.9992ohm. I would assume this is to compensate for switch and wire resistance.I would ideally like to get this back in spec. I am busy building proper Kelvin leads for my DE 5000 LCR meter before I make final measurements, especially on the low resistance resistors. Thank you SeanB I will contact Mr Pettis. I was thinking on the Vishay resistors as alternative.In the meantime I found a few PWWs on fleabay and ordered those, 20K 0.01% and 2 GR 10 ohms. If they measure out, half of my problems I can repair and then I can have the others made custom. Will post a few pics and a Video on this later.Rgrds

author: Vgkid
author_rank: Super Contributor
timestamp: July 31, 2017, 02:09:38 pm
content: For the 0.01992, and 0.00992 resistors get 0.02/0.01resistors and be done with it. Same for the next higher decade, but try paralleling another resistor for those.

author: cncjerry
author_rank: Unknown
timestamp: July 31, 2017, 10:35:38 pm
content: You can find Kanthol resistance wire on ebay. It is really popular now as it is used for vape coils. It comes in a lot of sizes and resistances per foot. I've made some pretty accurate wire wound resistors using it but I don't know how stable it remains. If you have an accurate 4wire meter you can attach a lead to one end (after zeroing out the meter) and then run the other end down the wire until you hit the target resistance. You can clip it from there. Again, I don't know its temperature stability and I assume there are other resistance wires out there. I would like to hear from people that use other wires.I have an ESI decabox and love it. It is one of my favorite pieces of gear.Jerry