HP Forum Archive 19

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HP 65 Repair Effort Message #1 Posted by ClausB on 2 Apr 2010, 4:05 p.m. I recently got a broken 65 off eBay. On power up it displays all 1s for a second and then goes blank. It has been repaired before because the logic board ROMs have later dates (7437) than the serial label (1333A 08230) and the main IC has a sticker dated '78. Also the card reader is clean and its wheel has new o-rings. Would anyone here happen to know the history of this unit? I printed the logic board layout from the May '74 HP Journal article and checked the power supply output with a DC voltmeter. I get these readings: Nominal _ Actual 3.75 _____ 3.8 (batt) 6 ________ 6.2 7.5_______ 7.7 -12 ______ -12.2 These seem OK, no? I also measured 2.9 DC volts at phi1 and 3.4 at phi2. Sound reasonable? I guess the next step is to scope some signals. Any other ideas? Edit: Can that serial number be right? I thought the 65 came out in '74. Edited: 2 Apr 2010, 5:59 p.m.

Re: HP 65 Repair Effort Message #2 Posted by Eric Smith on 2 Apr 2010, 11:30 p.m., in response to message #1 by ClausB DC voltages OK. To really tell whether the clock is OK, you'd have to look at it on an oscilliscope. The main signals to look at are: test hybrid ROM signal point pin pin ------ ------ ------ ------ Phi1 6 38 12 Phi2 5 39 10 SYNC 1 32 7 sync, pulse active 10 of 56 cycles IA 3 8 15 instruction address, CPU -> ROM IS 2 33 6 instruction, ROM -> CPU RCD 10 34 n/a reset cathode driver, every 15 words WS 9 30 14 word select, which digits are affected by instruction DATA 8 35 n/a 56-bit data word Pin information is from my own personal notes, but I think it matches Tony's schematics.

Re: HP 65 Repair Effort Message #3 Posted by ClausB on 2 Apr 2010, 11:34 p.m., in response to message #2 by Eric Smith That's very helpful. Thanks, I'll check those.

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