HP Forum Archive 06

[ Return to Index | Top of Index ]

Dyslexic (agnostic?) HP-67 Message #1 Posted by Michael Meyer, M.D. on 5 Nov 2001, 11:25 p.m. I have an HP-67 that doesn't believe there is a dog. Seriously. I just rebuilt an HP-67. Looks clean, and the card reader is now smooth. Only one minor problem. It doesn't work. It gives "error" when it reads cards, even with cleaning and checking connections. On a whim, I recorded a short program, used the calc to write it to a card, and read it in another HP-67. It recorded to the card and read fine in the other. So, I have a card reader that writes, but cannot read (thus the dyslexia). Where do I look next? Is the card reader now proven working, since it writes correctly? Am I looking at an irrepairable 67? Michael

Re: Dyslexic (agnostic?) HP-67 Message #2 Posted by Viktor Toth on 5 Nov 2001, 11:44 p.m., in response to message #1 by Michael Meyer, M.D. Michael, You're probably looking at a bad filter capacitor. I've had this exact same problem on several HP-67 calculators a few months back, and in each case, the problem was the large (tantalum) filter capacitor that filters the battery voltage (the largest valued tantalum capacitor sitting near the top of the main circuit board). Replace it and try again. Don't be misled if the old capacitor appears to measure correctly with a capacitance meter, the problem is with its increased ESR value. Even a smaller capacitor with a good ESR value should work fine as a replacement. Viktor

Did you hear about the dyslexic agnostic insomniac? Message #3 Posted by Bruce Cohen on 6 Nov 2001, 2:03 p.m., in response to message #2 by Viktor Toth He sat up all night wondering if there was a DOG.

Re: Dyslexic (agnostic?) HP-67 Message #4 Posted by Tony Duell (UK) on 6 Nov 2001, 6:59 p.m., in response to message #1 by Michael Meyer, M.D. Alas writing is a lot less critical than reading (no low-level signals for one thing), and anyway some parts of the circuitry are for reading only, others for writing only. So the fact you can write doesn't mean the reader is perfect. But there are many things you can check. Start with the pin contacts between the reader PCB and the logic PCB. 2 of them are the read data bits. If they're not making good contact, then you won't be able to read cards. Now check the leaf contact switch (on the front surface of the chassis, towards the keyboard PCB). I find that screwing the adjusting screws in until the leaves just start to lift is a good enough setting to get the reader working. The next thing to suspect is the capacitors. Since reading involves lower level signals than writing, it's a lot more susceptible to supply line noise. Check (and replace if in doubt) the capacitors on the reader PCB. And the electrolytics on the logic PCB -- particularly the largest one which is between the battery +ve line and 0V. It's a common cause of this fault. The other thing it could be is a faulty sense amplifier chip (on the card reader PCB) or Card Reader Controller chip (28 pin on the logic PCB), but let's hope not as both are HP custom parts.

Re: Dyslexic (agnostic?) HP-67 Message #5 Posted by Michael Meyer, M.D. on 6 Nov 2001, 10:24 p.m., in response to message #4 by Tony Duell (UK) THANK YOU, VIKTOR and TONY!!!! Viktor was correct, so the extra advice from Tony wasn't needed, but is always great to know!!! You guys are the best!! It reads, with a replaced capacitor (good use for a broken TI-59 board...)!! Now I don't have to be a dyslexic agnostic insomniac; sitting up at night doubting if I'll ever fix the rotaluclac! So.... next question. Another challenge: The display is dim on this calculator. Is there a way, easy adjustment or not, (replace resistor, etc.) that can brighten the LED display? Otherwise, I'll still have to sit up at night... to see the display in a dark room. Oh, the trials and tribulations of a calculator addict! Michael

Dog struck my Dyslexic calc dead! Message #6 Posted by Michael Meyer, M.D. on 7 Nov 2001, 1:57 a.m., in response to message #5 by Michael Meyer, M.D. Well, The calculator was working perfectly. Happily running programs. I started a simple loop to cycle the battery down for a recharge. After about two hours, the display froze into all 0's, of varying intensity. Now, even with a fresh battery, nothing. 0's. Dead. I even replaced the same capacitor again, suspecting it had failed. Nope. 0's. Dead. Oh, the pain. It seemed so happy; being able to read and write and all. And the case and keyboard were so nice and clean. It was so pretty, and too young to die. It will be missed by those (me) that loved it. I can still remember it running happily through calculatons, as if it were only minutes ago. Any ideas? So near...and now... so far. Calculator heaven? Can it be saved by surgery, or has it suffered heart failure? Viktor? Tony? Anybody? I don't want to be alone in my grief. Sniff. Michael

Re: Dog struck my Dyslexic calc dead! Message #7 Posted by Tony Duell (UK) on 7 Nov 2001, 3:58 p.m., in response to message #6 by Michael Meyer, M.D. The first thing to check (as ever) is the voltage outputs of the DC-DC converter circuit. The easiest place to check these is on the pins of the ACT chip -- the 22 pin chip on the logic board Take the back off the calculator, and find some way of powering it up through the battery contacts. If you have a bench PSU then it's easy -- just clip it onto the battery contact springs. Otherwise find some way of holding a charged battery pack in place (elastic band, friend, whatever) :-) You need to make 2 voltage measurements. In both cases, the common lead of the voltmeter goes to pin 12 of the ACT (ground). The first measurement is Vss on pin 1. It should be about 6.2V. If you have a 'scope, look for ripple there as well (it should be minimal). The other meassurement is Vgg on pin 2. It should be about -12V. Again check for ripple if you have a 'scope. If the DC-DC converter is fine, then alas I would suspect ROM failure. Maybe it was going to fail anyway, maybe it was zapped by static when you had the machine apart.

Re: Dog struck my Dyslexic calc dead! Message #8 Posted by Michael Meyer, M.D. on 7 Nov 2001, 6:34 p.m., in response to message #7 by Tony Duell (UK) Thanks, Tony, for your kind words of sympathy and advice. Well, the Vgg tests at 10.5v, but otherwise it tests as you described. I don't have a scope. Anything else I can look at (i.e. clocking transistor, etc.)? Otherwise, it was nice while it lasted. I've never had static problems before on my workbench, that I've been aware of. I sure hope I didn't murder it myself. I do try to be careful, but I don't wear a ground strap. I guess I'll start. It did run for a couple of hours, which I know is possible even with static damage. Is it possible that I wasn't the instrument of its death? At least I have an otherwise perfect calculator, should I ever find one with an irrepairable card reader, etc. Let me know if you have any last rites... I mean, other ideas. Thanks much, Michael

Re: Dog struck my Dyslexic calc dead! Message #9 Posted by Tony Duell (UK) on 7 Nov 2001, 6:59 p.m., in response to message #8 by Michael Meyer, M.D. That Vgg sounds a little low to me. The PSU is clearly running, but you might have problems with the output capacitors. Check the other electrolytics (actually tantalum) on the logic PCB. There's a 22uF (IIRC) from Vss to ground and a pair of 2.2uF in a voltage doubler circuit for Vgg. Check the lot. Yes, static damage can occur a fair time after the event that did the damage, so it could have been a static zap. Probably it was just time for it to fail, though, if it is a chip failure. There are other tests you can do (CPU clock, bus clocks and other signals), but all of them need a 'scope. Without one you're pretty much limited to checkking supply voltages.

Thanks Message #10 Posted by Michael Meyer, M.D. on 8 Nov 2001, 1:59 a.m., in response to message #9 by Tony Duell (UK) Tony, Thanks. I'll check the other capacitors when I have a chance. I've spent more time than I should already. Your help has been very appreaciated, as always. "Another Day, Another Calculator," Michael

Do never give up an HP calc.... Message #11 Posted by Vieira, Luiz C. (Brazil) on 8 Nov 2001, 1:59 p.m., in response to message #10 by Michael Meyer, M.D. ... they always surprise us. I'm no Tony Duell (no pun intended; I admire his posture a lot), but I believe each of us follows any situation like this both concerning our own fellas OR with the possibility of helping in any way. I will stay ansious waiting for good news from you. And from your HP67. Good luck.

Re: Do never give up an HP calc.... Message #12 Posted by db(martinez,california) on 8 Nov 2001, 10:43 p.m., in response to message #11 by Vieira, Luiz C. (Brazil) michael; i second what luiz said, and only wish to add that the rest of us are watching you like vultures (gallinasos); looking for spare parts. not really. just kidding. mostly. and honestly, good luck. seriously.

Re: Do never give up an HP calc.... Message #13 Posted by Michael Meyer, M.D. on 9 Nov 2001, 1:52 a.m., in response to message #12 by db(martinez,california) Hi all! Gosh, I love it!!! Yes, I'm going to give it another crack. And, yes, there are already those asking about the remains.... So, if I can't get it to breathe again, I'll post it for trade for something. I have a couple of working 67's, but this one is a beauty. Thanks for all the encouragement and help! This forum, with all the GREAT people who participate, is something our "community" can be very proud of!!! "Another day, Another calculator," Michael

IT'S ALIVE!!! *** IT'S ALIVE!!! *** IT'S ALIVE!!! Message #14 Posted by Michael Meyer, M.D. on 10 Nov 2001, 2:13 a.m., in response to message #13 by Michael Meyer, M.D. Dear all, Thanks for your continuing support on my dead HP-67. To borrow a phrase, you told me: "Never give up!! Never surrender!!" You asked for follow-up, and here it is: (Are you sitting down?) My HP-67 is ALIVE! Brought back from the grave! (Or was it a near-death experience? There was this light... and a line of zeros...) Mark Sims (texaspyro) suggested that all 0's was a sign of a bad ACT chip, as I believe Tony thought also. WELL, I removed the ACT chip from a broken HP-25 that won't program and has an awful case and worn keyboard (see my posting on playing football with HP calcs...) I substituted the ACT chip from my HP-67 into the 25. ALL 0's! O.K. so far. Then, I transplanted the "good" chip from the 25 to the 67. My dyslexic/agnostic/insomniac calculator is ALIVE AGAIN!!! There IS a DOG!!! My calculator is now again happily writing, reading (thanks to the new tantalum capacitor), and even displaying brighter (thanks to a new resistor), and running programs. Forwards and backwards, even!!! (Oh, that was ME standing backwards. Never mind.) Thanks for your condolences during by time of grief, and for all of your incredibly accurate and wise advice. Now I can sleep again... until my next venture. (I'm still looking for a functional lower power board to complete an HP19C.....) You people are all the greatest friends a guy could have. Just look at how many people attended the calculator funeral!! My tears have turned to tears of joy again. On to the next challenge!! As I like to say, (and I made this one up myself), "Another day, another calculator!!) This HP-67 will always have a special place in heart, though, as one saved communally by the HP collector community. Yours in gratitude, Michael

IT'S ALIVE!!! *** IT'S ALIVE!!! - (Best news of the last weeks) Message #15 Posted by Vieira, Luiz C. (Brazil) on 10 Nov 2001, 7:03 a.m., in response to message #14 by Michael Meyer, M.D. BEST NEWS OF THE LAST WEEK (at least in this forum). Great reading this. Best regards.

Re: Dyslexic (agnostic?) HP-67 Message #16 Posted by Tony Duell (UK) on 7 Nov 2001, 4:02 p.m., in response to message #5 by Michael Meyer, M.D. Yes, there is a resistor adjustment that will alter the display brightness. IIRC it's the resistor connected to pin 5 of the ROM0 chip (the 18 pin chip on the logic board) Theres' also a resistor, normally 51.1 Ohms (often mis-described as 511 Ohms !) on the keyboard PCB that adjusts the brightness of the middle (g) segments only, I think

[ Return to Index | Top of Index ]

Go back to the main exhibit hall