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Impossible to fry 67 without battery inserted? - Printable Version

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Impossible to fry 67 without battery inserted? - Andreas - 01-23-2004

Hi everybody, I read this forum quite often, mostly looking for repair tips, but also enjoying the discussions around other, less technical themes. I am the sad owner of a dead 67 still waiting to be re-animated, and until recently figured the unit must have been operated by a previous owner without a battery pack inserted. The other day I read (from Victor if I recall correctly) that the 67 is safe to be operated without a battery. I also concluded that the most likely source for the failure is the quite sensitive ACT chip, which if replaced would bring my 67 back to life. Checking the clock with a scope should be conclusive. I would appreciate comments on both issues.


Re: Impossible to fry 67 without battery inserted? - Patrick - 01-23-2004

It is not safe to use the supplied charger without a battery in place. You can get lucky, but the calc may get fried if the card reader is used or a current spike occurs w/o the battery. You can use a highly controlled external DC voltage source.

Re: Impossible to fry 67 without battery inserted? - David Smith - 01-23-2004

It is theoretically possible to damage the HP67 card reader chip if the charger is connected without a battery, but I have never seen this happen. There is a connection from the battery + contact to the card reader motor driver chip. The battery pack holds the charge voltage down below 5 volts. It can rise to a higher value if the pack is not installed. In any case the reader needs the high current from the pack to run properly.

The rest of the machine runs off the regulated charger voltage or the battery pack and would not be damaged. I have never seen a bad ACT chip among dozens of HP67 machines. I suspect that your problem lies elsewhere... check the power switch, charger bypass strap, battery contacts, battery wiring, etc.

Re: Impossible to fry 67 without battery inserted? - Victor Koechli - 01-23-2004

I second that. I have seen many classics, including 67s and 97s, being run off the charger alone for years, or even decades, with a dead battery in place or with no battery at all. It seems, although the 67 is electrically a Woodstock, that it behaves like a Classic here. I have also not seen the ACT chip problems in the 67 like in other Woodstocks.

Check for the obvious causes first, like contacts between the three boards, the power switch, and the bridge contact that connects the battery if the charger plug is not in place. Unplug the boards, clean the contacts, and reassemble.

Try to find out if power gets to the main PCB at all - the traces carrying the power are easy to locate. If you have power on the board, but not at the chips, the power supply is dead. There are other people in this forum who can help with circuit diagrams of the power supply.

Most likely, if you have come this far, your HP-67 will be alive. Keep us informed!

Cheers, Victor

Re: Impossible to fry 67 without battery inserted? - Andreas - 01-24-2004

I checked the obvious, but not the charger bypass, I'll do that next. Let's hope I jumped prematurely to a false conclusion.
I thought the 67 was based on series 30 technology, and thus prone to the same over-voltage issues. This would probably be a good time order the Museum CDs with the schematics. To be honest, I didn't dare to open it yet, as the back label is yet intact, and without a replacement board I didn't want to do surgery.
Thank you for your help, I promise to keep you posted!


Edited: 24 Jan 2004, 7:52 a.m.

Re: Impossible to fry 67 without battery inserted? - David Smith - 01-24-2004

The 67 is a woodstock machine, it just uses a real power supply. Verify that your charger is putting out good volts. Also try clipping a battery to the contact terminals. A lot of times the terminal have invisible voodoo corosion that keeps them from making good contact. They actually touch the battery contacts long the SIDES of the tip, not the curved top of the tip.