hp 97 with hot resistor - Printable Version +- HP Forums (https://archived.hpcalc.org/museumforum) +-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html) +--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html) +--- Thread: hp 97 with hot resistor (/thread-17322.html) |
hp 97 with hot resistor - martin - 05-13-2002 hallo, i am new here. may be you discussed such problems before, but i did'nt find any entry, helping me.
from a friend i received a not working hp 97 (newer version; made in brazil; only the upper led in the display is working). the tall resistor (visible after opening the back cover)was seperated. fixing it again, nothing changed, but this resistor is getting real hot (that's why it fell out). - thank you
martin
Re: hp 97 with hot resistor - David Smith - 05-13-2002 You most likely have a bad transistor or two or three or four or five or six in the battery charge circuit. The HP97 service manual with schematics is available on the HPMUSEUM CDROM set.
Re: hp 97 with hot resistor - Ellis Easley - 05-13-2002 I'm new to the HP97 myself. There is a complete service manual on the MOHPC CD-ROMs and also a user's manual for either the 97 or the 67, which works almost identically. As I recall from opening my 97, the only large resistor is the one that limits the charging current. There is also another resistor in series that is shorted out when the power switch is on, to allow the AC adapter to provide current for both charging and running the calculator. I just examined my machine, there is a 4.7 ohm 2W wirewound resistor next to the large chip (1820-1751) visible by just removing the bottom of the unit. Then on the keyboard PCB (visible when you unplug the circuit boards and remove the middle assembly), there are two large resistors. One is an 8.2 ohm 2W wirewound which I found is the one shorted out when the power switch is "on". There is also another 4.7 ohm 2W wirewound but it measures less than 1/2 ohm, it must be across a coil. I'll look at my MOHPC CDs later.
Re: hp 97 with hot resistor - Tony Duell - 05-13-2002 The HP97 (and all other Topcats AFAIK) includes a circuit to protect the machine from overvoltage if the battery pack goes open-circuit Re: hp 97 with hot resistor - martin - 05-14-2002 thank you for your helpful contributions,
the interior of my hp-97 is looking like this:
martin
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