2.2 Meg Trim Pot for R&S CMT-54 - Page 1
Forum section: electronics / repair

author: Marc M.
author_rank: Regular Contributor
timestamp: September 20, 2015, 02:51:35 am
content: Hi folks, I'm trying to locate a broken trim pot for an abused Rohde & Schwarz CMT-54 Service Monitor I'm repairing. The Focus and Intensity controls for the built in scope project out the rear of the unit. At some point the Focus control took a hit breaking both 'end' terminals off of the pot. Simple enough fix but unfortunately I can't locate a replacement pot.Straight from the service manual:R25RS 0,25W 2,2MOHM+-30%LIN. 803.0973POTENTIOMETERRUF 0473-300 2,2MOHM+ 30The pot itself is marked:RUWIDO 15 057 00 CSniffing around the usual suppliers (Mouser, Digikey, etc.) only list it in a surface mount package and even those aren't stocked. I'd certainly prefer a direct replacement, but would settle for anything small enough to fit inside the available space to make it functional.Any help locating something that will bring this old girl back to life would be greatly appreciated.Marc -

author: Deathwish
author_rank: Unknown
timestamp: September 20, 2015, 03:11:07 am
content: possible replacementhttp://www.bourns.com/docs/Product-Datasheets/0473.pdf?sfvrsn=0

author: DimitriP
author_rank: Super Contributor
timestamp: September 20, 2015, 03:16:24 am
content: The good news this set comes with 10, 2MO pots and a nice 20 drawere component cabinet.Bad news is it comes with a 20 drawer cabinet with another 190 pots you don't need and a price to match ($69.95)http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_85032_-1

author: DimitriP
author_rank: Super Contributor
timestamp: September 20, 2015, 03:31:53 am
content: Or this , if you don't want to wait for 6-7 weeks from Mouser....http://www.amazon.com/2-2M-Variable-Resistors-Trimmer-Potentiometers/dp/B008DFV3VE/ref=cm_cr_pr_bdcrb_top?ie=UTF8

author: Deathwish
author_rank: Unknown
timestamp: September 20, 2015, 03:32:46 am
content: http://www.ebay.co.uk/itm/3-x-2-2M-ohm-Vertical-large-carbon-preset-potentiometers-/321384101191?hash=item4ad3fc3547http://www.ebay.co.uk/itm/2-PCS-Piher-Trimmer-Preset-Potentiometer-2-2M-PT10V-/320530481685?hash=item4aa11b0215I have mounted Horizontal pots on veroboard and turned them into vertical mounts to salvage an item before.If it works it works sort of thing

author: Marc M.
author_rank: Regular Contributor
timestamp: September 20, 2015, 04:20:22 am
content: Man, you guys rock! I never thought about searching Fleabay in UK, DE, Etc. Dimitri, I just can't justify paying someone >$10.00 USD for a $1.00 part. Deathwish, that is the correct pot in the Bourns PDF (they bought out RUF). The problem is I haven't been able to find anybody that actually stocks it. Thank you for the perf. board tip. I've been using perf. board to adapt all sorts of crazy stuff since I started playing around with this stuff in the late 70's. Just before I checked the board, I was soldering the 2 broken off legs and the body and center pin to a piece of perf. board. The plan was to get everything lined back up (PITA, taking forever), then I would use hot melt glue to physically lock everything in place. Once that was done I was going to glob silver ink across the broken joints to re-establish the connections. There isn't much current running thru this so this method works as long as you have patience of stone and the time to invest.Somewhere I have a box of hundreds of trimpots I pulled from tube (valve) TV's way back then when this stuff was $$$$ and I was a broke teenager repairing TV's, stereos, etc. to supply my electron addiction. Plenty of high value pots back then with the high voltages associated with tubes. Plus every color TV had a convergence board stuffed with a dozen or so (though those weren't typically in the meg range). I know, I'm sick, but I miss those days of starring in a mirror tweaking pots trying to get the convergence as close to perfect (you could never get it perfect - always a trade-off). Unfortunately, it would be quicker to walk to China then find them buried in storage.I finally found one @ Newark/Element 14/Farnell's for reasonable cost. It's not the same style but I can make it work. I don't normally deal with them so I forgot to look there - doh!Meanwhile, I'll setup searches in Fleabay for the R&S number, the RUF number, and the Bourn's number. I would like to get the correct replacement since this is such a nice piece of gear.Thank you guys for the help!Marc -

author: Vgkid
author_rank: Super Contributor
timestamp: September 20, 2015, 06:20:38 am
content: If you werent able to find one, you could have used a 2Meg with a 100k on eack side.

author: Marc M.
author_rank: Regular Contributor
timestamp: September 20, 2015, 07:53:00 am
content: Quote from: Vgkid on September 20, 2015, 06:20:38 amBeen there, done that in the past, either balancing it out on both ends or sticking it all on 1 end depending on the specific application. In this case, all I could find in my misc. trim pot drawer was a 1 meg. Even with that I could tack resistors on each end to get it into the required range to focus the trace thru a reasonable brightness range but fortunately, I found one that will work @ Newark so I don't have to go thru all that.But a great tip none the less for the less experienced folks out there that happen to read this thread. Thanks for the input!Marc -