Keithley 169 teardown - What a pile of .... - Page 1
Forum section: electronics / testgear

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 16, 2016, 09:56:49 pm
content: I'm trying to post this for about the 10th time. The forum software is rather silly if your attachment file size is too large you can't simply reattach as you will get an error about posting again too soon or that you already posted this message. Very irritating.....I bought this meter from a university sale. I have always associated Keithley with quality products but this meter proved me wrong. The construction is a joke. There are four spacers only held in place by the proper tongue angle and you have to try to keep the board in place, the battery holder I place, the four spacers in place, the bail in place and put the bottom cover on. What a joke.The batteries had long expired in this unit (I took them out a few days ago) and the holder was ruined. The battery holder was the least of its problem as someone had tried reworking it and added some sockets to a few ICs and did a poor soldering job. The main IC, the Maxim part, is bad though and gets very hot within seconds. Take note of how the banana jacks are connected by fuse holder clips! The current measurement fuse is in a cheap plastic holder on the bottom cover so you have the current sense running all the way to the back of the board through two long wires to the fuse older. Also note the bodge on the top left of the board by the T092 cased voltage reference.I'll just scrap this one for parts and make a mental note to pass up buying any more of them.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 16, 2016, 09:58:10 pm
content: More photos

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 16, 2016, 10:01:18 pm
content: More photos

author: retiredcaps
author_rank: Super Contributor
timestamp: September 16, 2016, 10:08:37 pm
content: Scullcom's youtube channel has a handful of Keithley multimeter teardowns of roughly the same vintage.https://www.youtube.com/channel/UCDqryeq1kMDSEQwltWqASrA/videos

author: ModemHead
author_rank: Frequent Contributor
timestamp: September 16, 2016, 11:11:50 pm
content: First time I've seen inside a 169. Not exactly impressive, although it does appear to be a lower-end model based on the ICL7106. Which are still available in 40-pin DIP, BTW.Also, I'm relatively sure the meter comes apart by pulling up the top half of the case, leaving the front panel and circuit board in the bottom half.A couple years ago I acquired a Keithley 197A, and the inside looks like a work of art to me. Probably an unfair comparison, in their day I'm sure there was quite a price differential.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 16, 2016, 11:37:49 pm
content: After looking at a few of the videos on the link above which show the screws with a rubber oring around them to keep them in place on the bottom cover. This allows taking the screws loose and turning back over to disassemble from the top as you said. This would make things easier but the loose spacers is still a very poor design choice. Looking at the inside of the meter in your photo and the video it is obvious the 169 does not hold a candle to them.

author: Muxr
author_rank: Super Contributor
timestamp: September 16, 2016, 11:39:31 pm
content: Quote from: Jeff_Birt on September 16, 2016, 09:56:49 pmI just useimgur.comand then link them here. Imgur automatically trans-compresses the images. You just gotta wait till they are fully uploaded, right click on the image and copy address. Might save Dave bandwidth as well.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 17, 2016, 08:15:14 am
content: Really not impressive, but that is what you can expect from the low end of that time. At least the board is FR4 and not phenolic, single sided. If this an external reference they already did some extra expense - they could have used the internal one. They seemed to have saved that money on the caps around the ADC though.The ICL7106 should be still available. As this chip is directly driving the LEDs it is normal to have quite some power dissipation. Given about 8 mA per segment and maybe 20 segments active, that is something like 160 mA with about 3-3.5 V of drop inside - so about 500 mW. Though with some thoughts they could have moved some of the voltage to external diodes - but that takes thinking beyond the typical circuit shown in the data-sheet and a few more cents.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 17, 2016, 02:15:53 pm
content: This unit has an LCD screen that is held into place in the shoddiest way possible (photos below). The part I believe to be an external reference is marked MPS 5010, I can't locate a datasheet on it but I have seen it show up in MTE cross reference charts as a 1.2V zener reference diode.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 17, 2016, 02:21:23 pm
content: Here is a shot of the reference diode and a strange variable cap?

author: tronde
author_rank: Frequent Contributor
timestamp: September 17, 2016, 02:43:25 pm
content: Beware that the ICL7106 is an ICL7106Rwhich means the leads are reversed (flipped upside-down).

author: TheBay
author_rank: Unknown
timestamp: September 17, 2016, 02:44:16 pm
content: That looks really quite shocking, somehow it looks sort of generic and probably not even made by Keithley, it doesn't even seem to say Keithley on any of the boardsso think this is some oem generic thing of that era with a Keithley case & badge, probably to fill a certain market segment.Had a look at similar meters to see if something else shares the same board, but couldn't find anything.

author: TAMHAN
author_rank: Frequent Contributor
timestamp: September 17, 2016, 03:47:49 pm
content: Hello,speaking of my 177, I can remember a similar green PCB. Sadly, the pictures of it went titsup when my phone crashed ;(

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: September 17, 2016, 03:55:22 pm
content: Quote from: tronde on September 17, 2016, 02:43:25 pmYeah, that confused me at first when I was looking at the datasheetI have now salvaged a few things off the PCB and the banana jacks from the front panel and the rest was scrapped. I kept the case since it seems to be used on other Keithley models.

author: bitseeker
author_rank: Super Contributor
timestamp: September 17, 2016, 08:03:45 pm
content: That was interesting to see, given how much worse it is than other models in similar enclosure. Thanks for the warning.