Electronics > Repair

Series defect on agilent 167xx boards?

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DoricLoon:
Thank you very much for the help Mark.

With the information you passed on earlier I discovered that the 7k5 resistor in the divider for U29 was in fact measuring 8k. Swapped the resistor and I have fully functional 16752A

Beauty.

Came on to post my results and I see your further post which has the information I had just noted down about the DAC to comparator pin out.

So for my low order bits on pod 4. Comparator U29 (pin39) to junction of (560R - 7k5) - DAC U39 Voutg (pin34), trace goes pretty much full length of the card.

Now to clean up the area's where the runners were and stick them on with new adhesive. I purchased a roll of 3M VHB clear foam tape 6mm wide 1mm deep. Hopefully it will play nicely with the PCB?

Thanks again  :-DMM

MarkL:
Great - glad you found the problem!

That's what I was going to try too - the thin 3M VHB tape, but I have some of the gray variety sitting around.

For now, after cleaning the boards, I left the runners off and I'm being careful with them.  I'm probably going to regret it after I rake several components off the bottom, and THEN I'll put the runners back on.

keitheevblog:
Thanks so much for this dialog --- it's nice to see such detailed posts and information!

I'm looking for an appropriate replacement adhesive for the runners.

How's that 3M stuff working out? Have you found any adhesive that claims it is specifically FR-4/PCB safe?

Keith

EDIT: Sorry I know the thread is about a month old.....not too too stale, I hope. :)

DoricLoon:
I've still not got around to sticking the runners back on. Roll of tape at the ready but that's as far as I've got. When I read the data sheet it sounded like the 3m tape should be safe? I guess that any issues with it would take a long time to transpire anyway. I did wonder if it would be a good idea to put on conformal coating first, just incase the adhesive doesn't play nicely?

keitheevblog:
Yeah conformal coating down first sounds like a good idea.

My question was whether the pro-active approach to runner removal is a good idea or not. In boards where there are no visible signs of corrosion that are otherwise self-testing fine?

It occurred to me while I was removing them that you could possibly damage a board that worked fine.

Do you guys have an opinion on that?

I've been using a heatgun setting on low and trying to evenly heat just the runner. While the heat helps the adhesive release, I worry about these super tiny 0201's (or whatever) accidentally re-flowing. I'm guessing the surface tension would keep it in place.....but who knows?

My technique has been to use a plastic pry tool to get under an edge, and then wand the heatgun back and forth over the runner, all the while applying a lifting force. The runner does sometimes "pop" violently off the board.

I have noticed that the adhesive tape is both still sticky and flexible.....not hard.... and that I've been able to, in 95% of the cases lift the adhesive tape AND the plastic runner off fully intact.

Am I doing this right?

Thanks

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