{"id":8815,"date":"2020-09-11T14:14:00","date_gmt":"2020-09-11T04:14:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2020\/09\/11\/hp8640b-counter-repair-discretion-or-valor\/"},"modified":"2025-07-22T01:24:44","modified_gmt":"2025-07-21T15:24:44","slug":"hp8640b-counter-repair-discretion-or-valor","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2020\/09\/11\/hp8640b-counter-repair-discretion-or-valor\/","title":{"rendered":"HP8640B Counter Repair — Discretion? Or Valor?"},"content":{"rendered":"

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Inspired by BH1RBG, I cracked open the HP8640B to have a look at the counter circuitry. Above is the view that greeted me. That is the main counter board after I pulled it out of its socket. You can see the seven little red LED display modules. <\/b><\/p>\n

It is not as bad as it looks. In fact, I found the construction and accessibility of the HP8640B to be quite impressive (much better than the Tek 465 with all its flaky plug-in transistors). The manual has good, detailed info on how to get into the various compartments, and even as you work, instructions on which screws to remove or loosen appear on the tops of each RF-tight compartment. Nice. This thing was obviously built with the needs of a future repairman in mind. <\/b><\/p>\n

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Above is that same board flipped over. Again, not as bad as it looks. <\/b><\/div>\n

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Above is board A8A3, the board that I suspect is causing me trouble. When I go through the troubleshooting routines in the manual, I get to the point where they check decimal point position. Everything is fine UNTIL I GET TO 16 MHZ. Then the decimal point is not where it should be and the frequency displayed is very wrong. (This is in the internal mode — the counter works fine with an external signal source). The manual then sends me to Service Sheet 15 which points to possible problems on this A8A3 board, U3, U7 or U6D. <\/b><\/div>\n

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Troubleshooting this will be tough. I do not have the extender board that would allow me to test this A8A3 board with the other counter board raised up above it and operating. BH1RBG noted that getting the extender boards is almost as tough as getting the HP8640B itself. <\/b><\/div>\n

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While it really bugs me (!) to have a part of this device not working properly, I could just leave it as is. The signal generator is working fine, and I could use the external counter input to check the frequency. But this is a real kludge. <\/b><\/div>\n

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What do you folks think? Fix it or leave well enough alone? Discretion or valor? Anyone have an extender board? Any ideas on where the fault might be? <\/b><\/div>\n<\/div>\n

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Inspired by BH1RBG, I cracked open the HP8640B to have a look at the counter circuitry. Above is the view that greeted me. That is the main counter board after I pulled it out of its socket. You can see the seven little red LED display modules. It is not as bad as it looks. … Continue reading “HP8640B Counter Repair — Discretion? Or Valor?”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":8816,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-8815","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorised"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/8815","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=8815"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/8815\/revisions"}],"predecessor-version":[{"id":8819,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/8815\/revisions\/8819"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/8816"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=8815"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=8815"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=8815"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}