Threaded Mode | Linear Mode

albertofenini · 02-15-2019, 09:52 AM

Hi Tony,
I can certainly do this by de-soldering the pin, and eventually re-solder after the test,
I can even try to connect the WB to the logic board with a cable, and see if something changes.
Keep in mind however that one of the three card readers has even been tested on an HP67
and it was proven to read and write correctly.
Will do that and will post the results... thanks for the idea !

albertofenini · 02-15-2019, 02:00 PM

Tony read below,
is an excerpt from a very hold post about a strange behavior from an HP67.

http://www.hpmuseum.org/cgi-sys/cgiwrap/...?read=9683

Look like changing the capacitor in a near by of Vbatt was the solution.
Being mine an HP65 does anyone know where I can find the capacitor that regulates Vbatt ?
Thanks for help, Alberto

Re: A weird HP-67 card reader problem - SOLVED?
Message #10 Posted by Viktor Toth on 12 June 2001, 8:13 p.m.,
in response to message #9 by Tony Duell
Thanks for your valuable advice! I saw no signs that the capacitor across Vbatt would be the culprit, but I decided to try changing it anyway. Well, guess what... to my considerable surprise it seems to have solved the problem. I am going to try and see if this solves the issue on the second CPU PCB as well.

What is the nominal value of this capacitor? I tried to measure it, and my meter says it's around 50uF, which seems way too high. The highest valued tantalum I had in my toolbox is 15uF, and that's what I used as a replacement, and that seems to work fine.

Well, this was educational to say the least. Thanks again to everyone who tried to help!

Viktor

teenix · 02-15-2019, 08:27 PM

(02-15-2019 02:00 PM)albertofenini Wrote: Look like changing the capacitor in a near by of Vbatt was the solution.
Being mine an HP65 does anyone know where I can find the capacitor that regulates Vbatt ?
Thanks for help, Alberto

See attached image - looks like a 60uF capacitor.

The 60uF Tantalum capacitors that I can see are expensive - around $90.00.

A 10 Volt 47uF to 68uF should do.

teenix · 02-15-2019, 08:42 PM

It looks like the HP65 PCB is multilayer, so it would be wise to be careful replacing components. If the via (component hole) that connects the layers gets damaged it could be messy to try and repair it. You may not be aware that the middle layer has disconnected itself.

cheers

Tony

AndiGer · 02-15-2019, 09:06 PM

Alberto, I thought you checked this already as I pointed to the capacitor in the old thread in post #40. Good luck
Andi

albertofenini · 02-15-2019, 10:15 PM

Hi Folks, this is what we did ...
We modified two different card readers, one is HP65 style AMP 1826-0185 and one is HP67 style AMP 1826-0322.
For both we removed PIN 5 (WB) and we added a wire to the card reader PCB, so that we could capture WB before it reaches the logic board.
WA, RA and RB have been left connected to the logic board as GND and the two power lines.
Both card readers still read and load the card.
We have captured WA and WB.
WA looks normal, while WB looks flat and only change status once or twice.
If we connect "on the fly" WB to the logic via the wire, it gets noisy as when is connected thru the usual golden pin.
We also changed C3 (60 microF capacitor) and the results where very much the same,
except that we had to adjust the eccentric cam to keep the machine reading.

When looking an the scope snapshot please keep in mind we compressed the Volt scale as
WB change status only very slowly compared to WA, and it was looking almost flat.

wallyt · (This post was last modified: 02-22-2019 02:26 PM by wallyt.)

Hi all, regarding my HP65 mentioned earlier that seemed to have a definite preference for battery pack voltage, I think I fixed it. I replaced the capacitor (C3 ?) that was adjacent to the sense amp IC with a new 68uF axial tantalum. The unit now reads and writes under any condition without problems.

albertofenini · 02-22-2019, 02:58 PM

Hi Wallyt,

could you post a picture ? Both for the position of the capacitor and for the capacitor itself ?
We'll give it a try, even if we have already changed all of the three capacitors with no improvements at all.
The situation is always the same, if WB is connected to the logic board it's noisy if it's not connected
it's clean (see my last post) but totally different from how it should look

Thanks again

wallyt · (This post was last modified: 02-23-2019 02:33 AM by wallyt.)

Alberto, I put the unit back together before I got your message but here is a photo of a similar unit with the cap marked by the arrow. I used a 68uF 10V axial capacitor so it would fit alongside the IC.

albertofenini · 02-23-2019, 11:03 PM

Don't worry, but what kind of capacitor did you use ?
Tantalium ? Electrolitical ? Thanks Alberto

wallyt · (This post was last modified: 02-24-2019 03:19 PM by wallyt.)

This is what I used. I was going to replace the two caps that are in series with the head (22uF) but it wasn't necessary. I even purchased something to put across the motor but, again, it wasn't needed. So far everything is working as it should. I was lucky, your problem might be different.