Does anyone know the IC "1GM1-4239" and where to get its datasheet? - Page 1
Forum section: electronics / repair

author: blacknoise
author_rank: Contributor
timestamp: February 01, 2015, 03:06:10 am
content: Does anyone know a location to get a datascheet for the IC: "1GM1-4239"?This IC is used in the 50-Ohm front end of an Agilent DSO9254A. I think it works there as a programmable amplifier or attentuator.In the DSO9254A i try to repair, this "1GM1-4239" shows the following error:While in the upper input ranges (50mV, 100mV, 200mV, 500mV, 1V) anything is OK, in the lower input ranges (1mV, 2mV, 5mV, 10mV, 20mV) the "1GM1-4239" injects a current of about -0,2mA into the 50-Ohm input resistor.This results in an offset voltage of about -10mV at the 50-Ohm input. Too much to be compensated by the auto calibration...As a quick hack - far away from any professional repair - i connected a 25kOhm resistor beetween +5V and the 50-Ohm input. The resulting current across this resistor (+0,2mA) compensates the DC offset to 0V.And after this "hardwired compensation" astonishingly all other parameters, the channels voltage sensivity, its frequency response and rise time are fully in the specs, and equal to the remaining three channels of the scope.The "only" fault of the "1GM1-4239" seems to be the strange input error current in the lower ranges...Many thanks for any help!Kind regards

author: German_EE
author_rank: Super Contributor
timestamp: February 01, 2015, 10:06:18 am
content: If you have watched any of Dave's teardowns of HP/Agilent equipment you will know that they have a nasty habit of relabelling semiconductors with their own internal part numbers. This is a major pain in the ass. Your only option is to find out the REAL part number by trawling through all the manufacturers datasheets until you find a device with the same pinout.I suggest that you start with Microsemi and Hittite Microwave Corporation.

author: German_EE
author_rank: Super Contributor
timestamp: February 01, 2015, 10:08:49 am
content: I just had a thought, a lot of those digitally switched attenuators use a minus voltage to ground on the control lines, check that all the control lines are the same.

author: blacknoise
author_rank: Contributor
timestamp: February 01, 2015, 11:28:40 am
content: "...use a minus voltage to ground on the control lines..."...which could "break through" (as a current) to the input - do to a failure in the IC or due to a "to negative" level at a control line, maybe because of a failing zener limiter diode, or so...!?Interesting, i'll check this out - many thanks!

author: German_EE
author_rank: Super Contributor
timestamp: February 08, 2015, 10:48:49 am
content: Well, let's see:1) A company operating from a GMail address that can't afford a proper website, just something on blogspot..2) You can't decide if you're called Allicstock or flexiledco3) As a new member you have four posts in the last 24 hours, offering LED strips, parts for CNC machines, PCB manufacture and data on RF ICs (I detect a certain lack of focus here).4) Rather than just post the information you want people to visit your blog.Have I missed anything here?

author: blacknoise
author_rank: Contributor
timestamp: February 08, 2015, 03:27:29 pm
content: Quote from: German_EE on February 08, 2015, 10:48:49 am?? Ops - is it possible, your post hit the wrong thread ?? ;-)Regarding my initial question: Currently i am "somewhat" confused - after an auto calibration the offset error appeared in the 1-MOhm setting, but not longer in the 50-Ohm input mode!And to top this mystery, after each auto calibration the offset error "switches". One time it appears in the 50-Ohm setting, next time in the 1-MOhm setting...!?Following the BNC input a relay switches the signal to completey independant front ends, one for 50 Ohms, another for 1 MOhm. Obviously the offsets of both stages have to be adjusted separately - but until now i do not understand why the auto calibration fails to handle that instead of "toggling the error"...Kind regards

author: German_EE
author_rank: Super Contributor
timestamp: February 08, 2015, 05:40:28 pm
content: No, my post didn't hit the wrong thread. These places that offer to do everything from sourcing components to solving the energy crisis annoy me because they seldom deliver. The company operating from a GMail address is a big red flag. The other thing that annoys me are the places that appear to offer just the data sheet you need but, after you fight through the Chinese using Google Translate are only interested in selling you chips in bulk.I take it that you have had no luck finding the original part number of the chip. I had a thought about your offset 'switching' and the best explanation I can come up with is that the calibration routine switches one internal line an odd number of times, leaving alternate results at the end of each cycle.

author: blacknoise
author_rank: Contributor
timestamp: February 08, 2015, 06:16:44 pm
content: Ok and sorry, now i think i understand you.And yes, i found some, ahem: more "remarkably" than "respectable" ;-) sites who offer (or seems to offer...) this chip - from about $80 to $400++ USD......but for the first, i was only looking for the datasheet, to try to understand the failure. And since the failure is now toggeling - new insight: randomly (sometimes two calibration runs were needed to toggle the error beetween the 50-/1M-Ohm mode!), i meanwhile doubt that the "1GM1-4239" is the source of the failure.For the next i'll focus the (possibly for the 50- and 1M-Ohm frontends somewhat shared) offset compensation circuits, and maybe some file(s) with calibration data.

author: parawizard
author_rank: Regular Contributor
timestamp: January 18, 2025, 09:16:28 am
content: Quote from: blacknoise on February 08, 2015, 06:16:44 pmDid you get this repaired?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 18, 2025, 11:10:24 am
content: they seems to be found at price who defies any logic and maybe some fakes .... 10 years laterhttps://www.worldwayelec.com/pro/altech-corporation/1gm1-4239/2832994?