A Full Teardown of HP 8642B - Page 1
Forum section: electronics / testgear

author: AlphZeta
author_rank: Regular Contributor
timestamp: September 09, 2014, 01:51:06 am
content: OK, I did an LCD mod and showed a couple of pictures of my HP 8642B a week ago (https://www.eevblog.com/forum/testgear/hp-8642b-backlight-mod-and-easter-egg/msg505548/#msg505548) and during the process I also did a full teardown of the unit since I don't think anyone else had done a teardown of either HP 8642A or HP 8642B yet.Anyway, here is the link:http://www.kerrywong.com/2014/09/08/hp-8642b-teardown-pictures/Enjoy!

author: idpromnut
author_rank: Unknown
timestamp: September 09, 2014, 04:17:57 am
content: Wow! Thanks for the teardown; I was kinda iffy about doing it as I'm not strong in the RF front. Any tips for pulling apart this kinda equipment and then putting it back together (so that it actually works)?

author: alex.forencich
author_rank: Frequent Contributor
timestamp: September 09, 2014, 09:03:23 am
content: Quote from: idpromnut on September 09, 2014, 04:17:57 amDon't lose any screws? There really isn't anything special about it so long as you don't damage any of the connectors or lose any of the parts. I have pulled apart numerous bits and pieces of high frequency equipment and put it back together again with no issues. I even transplated a tracking generator from an 8594E to an 8593E, which required more or less completely disassembling the RF section and then putting it back together again. The only thing I would avoid doing is taking things apart that aren't meant to come apart. Some of the RF enclosures are welded or glued. If you take all the screws out and it doesn't open, don't force it.Also, the picturehttp://www.kerrywong.com/blog/wp-content/uploads/2014/09/A13A2_4.jpgdoesn't contain distributed element filters, it contains transmission line matching networks for a pair of amplifiers. Actually, if you follow the signal path from the left-most connector, you get: dc block, matching nework, amp, biasing, DC block, amp, biasing, DC block, balun, diode modulator, balun, dc block. This particular module in my unit actually has an intermittent issue, though I have not yet been able to track down the precise cause.The filter board also contains a very nice set of pin diode RF switches, though they are a bit easier to see on the schematic than on the board itself.

author: tszaboo
author_rank: Super Contributor
timestamp: September 09, 2014, 09:44:03 am
content: Wow, oldschool RF stuff. I is kinda strange to see TH components next to PCB RF magic. Thank for sharing.

author: KJDS
author_rank: Super Contributor
timestamp: September 09, 2014, 10:17:06 am
content: Take pictures, lots of them.If you take six screws from a lid, put them in a jar and label it. As you're taking them out, make sure they are all the same length. Occasionally, one will be longer or shorter for a reason. Sometimes this reason is important. Sometimes the reason is the operator picked up a wrong screw.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 09, 2014, 10:42:15 am
content: QuoteActually, I think these are feedtrough capacitors.

author: AlphZeta
author_rank: Regular Contributor
timestamp: September 09, 2014, 12:35:44 pm
content: Quote from: idpromnut on September 09, 2014, 04:17:57 amWell, as @alex.forencich said, the only thing you really need to pay attention to is not to damage the RF connectors. Fortunately, if you use the wrench that comes with the equipment, you can't really over-tighten as it doesn't provide much torque. As a rule of thumb, hand tighten the connectors first and use the wrench to further tighten the connectors a quarter to half turns.Also, one good thing about these modules is that the screws are all the same, so you don't have to worry about which screw goes where...

author: German_EE
author_rank: Super Contributor
timestamp: September 09, 2014, 04:48:24 pm
content: "Also, one good thing about these modules is that the screws are all the same, so you don't have to worry about which screw goes where..."That's just good engineering practice. Two years ago I helped somebody build an Elecraft K3 transceiver and there were about ten different sizes of screw, some of them differing by only a couple of mm. It took longer to verify the parts list than to build the equipment. IBM went the other way when they designed the PS2 series of machines and a lot of the parts clipped together with no screws required, they were a dream to service.

author: AlphZeta
author_rank: Regular Contributor
timestamp: September 09, 2014, 05:32:23 pm
content: Quote from: PA0PBZ on September 09, 2014, 10:42:15 amYes you are right... I will make correction on my site later today. Thanks.