GenRad 1689M RLC Digibridge Ram battery failure

Tubenut · **Posted:** May Fri 25, 2012 12:23 pm

Well, it's been about a month since we had a lightning strike down the road here. It blew part of the roof off of our "not so close" neighbors house. I talked to the family in the house, they were all home when the bolt went into the house. It was all over our local news and made it to TV. Anyways, when this happened, the power went out over here for a few seconds, then came on again. I didn't think anything of it, and the days past. I turn on my GenRad to find it's displaying 1.0000 and 1000, will not zero and is displaying error codes randomly. So I find them listed new from IET for around $9000... Yikes! I call IET and ask to speak to a tech about this unit. We chatted about its issues, he was helpful but wasn't familliar with the way it's acting and said I should send it in. They would change the RAM to a Dallas IC (battery inside the IC) and re-program it's parameters for a meger $1600. "A" Im in the middle of a project for a large company and need it now, "B" I would have to send it to their facility down in the States and deal with shipping and insurance on a big heavy item. So I started researching the net and found a service manual with the programming procedure, now all I need is some resistor standards. I have a gazillion resistors so I decided to take on the re-cal challenge. I designed a board with sealed reed relays and a lot of room for resistor swapping. I have a fully functional ESI Video digibridge, so that was the tuning tool for the new standard. So 3 days into this project and I have a decent standard. The resistance is very accurate to what the manual wants. The manual uses examples that are not right on. As long as the values are known, the GenRad will use it against it's internal standards to trim them electronically. So I replace the dead RAM battery and programming I go. I first had to determine the exact resistance and "Q" of the resistors in "ppm" before I start. This was done on all four standard resistors in the home brew box (thanks to the ESI) After a crazy programming procedure via the front panel on the GenRad, all works and displays accurate compared to the ESI and my new Agilent Technologys meter. I'm HAPPY!

Here are some Pix of the GenRad and test fixture/calibrator I built. It took many hours :shock:

of mixing and matching resistors in series and parallel to get good accuracy. You can see in the first picture, a loop of Nichrome wire, used as a trim for the 24.9 Ohm standard. It trims to 24.900 quite well. All the rest have the same level of accuracy too. More than the re-cal procedure requires.

Here is the Genrad

Some Pix of the cal box I slapped together.

The same procedure to do the PCB layout with toner transfer, put the lettering and numbering on the face of the unit..

MarkPalmer · **Posted:** May Sat 26, 2012 5:48 am

A very innovative way to work around an expensive problem. It is obvious you put a lot of thought and time in to the design of your calibrator, it looks well designed and constructed. I noticed a while back that much of your test equipment was well beyond the caliber found in the average hobbist electronics shop and figured it was used for your profession also.

-Mark-

Tubenut · **Posted:** May Sat 26, 2012 7:56 am

Thanks for the nice comment Mark. You are correct, I also use this stuff to make the "green" and other colors (I'm in Canada.) I like to post this stuff when there is not a lot of info available on the net. Maybe this will save somebody, some money or grief down the road...... At least help them in some way. We own a BMW X5, and it has been a constant source of problems. So when ever it give us grief (which is a lot) , I will back engineer or just fix some of it's electronic issues and post it on a BMW forum. Lot's of "Thankyou's"
I enjoy reading your "writeups" here on the forum Mark. It's nice to see people with solid contribution.

wd5jfr · **Posted:** May Tue 29, 2012 8:54 pm

One day back in the 80s when we lived in Denver I heard a humungous bang in the house as I was programming on a DEC LSI-11. I wondered what it was but was too absorbed and busy trying to get rid of a bug. Then we found that the dryer, garage door opener. some small appliances and sprinkler system had failed. The lightning apparently hit the chimney and found its way to ground through the failed units. After being puzzled about the selective nature of what failed I checked the house ground rod and found that clamp had corroded from electrolysis and fallen off. Whoever installed the clamp used one of the wrong material and because it was exposed to one of the sprinkler heads and the regular watering of only two years resulted in "uncathodic" protection. The strike didn't get any of my test equipment, computers or peripherals or ham gear. My ham gear had a separate ground system.
Nice job on the calibrator, thanks for showing it.
Hank

Tubenut · **Posted:** May Wed 30, 2012 12:56 am

Thanks Hank for the nice comment! I hear it's rare to get a direct hit of lightning. So you, and our neighbor need to go buy lottery tickets

The family that got struck had quite an intense story too. We don't get a whole lot of lightning around here....And thats fine with me.

7jp4-guy · **Posted:** May Wed 30, 2012 1:03 am

Nice work! Do you have any more details on that toner transfer process? I am working on labeling the case for a new project and that looks like an ideal way to do it. I have tried toner transfers before, but I always have trouble getting the toner to release from the paper. What kind of paper do you like?

-Matthew

Erik K · **Posted:** May Wed 30, 2012 1:50 am

Let me know if you want some L or C standards set up, in case you need those for other parts of your recal. I have a 1688, although it hasn't been to the cal lab for five years, and I'd be happy to spec some for you.

Tubenut · **Posted:** May Wed 30, 2012 2:40 am

Hi 7jp4-guy. I'm working on a new project and found some great paper! I used to use HP flyer paper and found it was good. Well, I ran out and was sceptical about this new Staples paper...... WOW!!!! This new paper is Absolutely great. The toner transfers so well to a circuit board, Acetone has a hard time getting it off. The Trick>>> It needs to be Inkjet paper you feed through your laser printer. The toner will not fully adhere to it, so it transfers easier. Also.... It has to be glossy.... The gloss seals around the toner causing it not to flatten out or bleed to ajacent traces. The Staples product # is 12486. I have a modified laminator that I use for the transfer process. This also really helps to make flawless circuit boards. The laminator has a circuit I built that controls the temp at 200 degree's F.

Hi Erik K. Thanks for the offer on tuning cal resistors. I have an ESI Video Bridge that I used to tune the cal resistors, here. It does a great job.

7jp4-guy · **Posted:** May Wed 30, 2012 4:51 am

Thanks! It never occurred to me to try paper made for an inkjet.

-Matthew

GenRad 1689M RLC Digibridge Ram battery failure

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