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Old 28th February 2011, 08:22 PM   #1
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Default HP 3478A Display

I have had the HP3478 for some time now, works great. Long story short I had sent it out for a NIST cal a few weeks ago. The meter worked great for another week then the display started to go out. I opened the meter and re-seated the cable from the main board, no change. I can press on the back of the display board and the read out is fine. There are two chips on the back of the display board covered in epoxie. One of them appears to have lost connection. I guess the IC's are wave soldered then covered with epoxie to keep them from breaking loose. My question is there a way to repaire the board? I looked everywhere for a replacment display and can not find one. Dose any one have 3487A that they scraped with a good display or a source to repaire for the display board. Any help would be great!
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Old 3rd March 2011, 01:12 PM   #2
macboy is offline macboy  Canada
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If what you see is just a blob of black epoxy, then what is in there is a bare die attached to the PCB with die wires bonded directly to PCB traces. It is not generally repairable.

You mentioned it works with pressure applied. Maybe you could try to fit some brackets and foam rubber in there somehow to press on the board?

As a last resort maybe you would want to try to reflow the suspect board, using either a toaster oven or hot plate. Google for "toaster oven reflow" or "hot plate reflow". This may help in cases of a BGA component having a bad connection underneath, but I don't think it would have much effect with epoxy blob ICs. As I said, it would be a last resort.
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Old 3rd March 2011, 02:11 PM   #3
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MB, Thanks' for the reply. I did some more reseach as as you stated , bare die, Ball- grid- array, covered in epoxy. No rework shop will touch it either. For now I have a mickey mouse work-a-round. Took a tooth pick and have it wedged between the main board and the device. That is working for now, still looking for a long term fix or now spair parts unit. I purchased a replacement from a vendor on E-bay
HP Hewlett Packard 3478A DMM, certified, NISTcalibrated - eBay (item 310227290925 end time Mar-13-11 11:59:06 PDT)

He accepted a little lower price than he was asking, still a little more than I wanted to spend. I have to say it was well worth it. The unit came Fedex at no added charge, and looks like new inside and out. The reading are dead on all fields. Came with full NIST cert report and includes another cal for FREE in 13 months. They even have a real phone number and real support, more than I seen on EEK-Bay in a long time. It's nice to see quality like this on Ebay. The guy I spoke to "Joe" told me they do not sell junk and stand behind all there products. I would buy from them again and again. Just thought I would add that if anyone is looking for high quality test equiptment with no risk involved.
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Old 3rd March 2011, 04:20 PM   #4
macboy is offline macboy  Canada
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You are not the first person to speak highly of Teletek around here. They seem to be reputable.
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Old 4th March 2011, 05:19 AM   #5
tomchr is online now tomchr  United States
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I've bought a couple of pieces of gear from them. I've been happy with them.
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