HP 67 Circuit Board

[teenix]

Hi all,

Alberto was kind enough to share some pictures of a bare HP-67 circuit board with me.

I sat down and re-engineered it and when it seems ok, I will upload the gerber files to a PCB manufacturer where anyone who wants one can get them made.

The minimum manufacture quantity is usually 5 pieces which is the same as one piece, so maybe if some are needed in the same area/country then they can get together and order them via some nice person. Once delivered, the forwarding postage will be cheap. There is no point me stocking them, as the onwards overseas postage is too crazy.

The cost will be in the vicinity of $US5 for 1 lot of 5 boards plus initial delivery charge.

I have the design layouts here if anyone wants a look and maybe offer a comment, especially if there is an error.

http://www.teenix.org/HP67.pdf

cheers

Tony

[Dave Frederickson]

Hans used JLCPCB for the FRAM71B DIY Expansion Board. Five boards cost $10.
https://jlcpcb.com/

[teenix]

Sorry, Dave,

I meant $US5 for the 5 boards. (Post updated)

cheers

Tony

[Tapti]

Hi Tony,
many many thanks for the HP67 schematics, they are of great value regarding my problem with the power unit of my maschine.
Stefan

[teenix]

Hi all,

I uploaded all of the HP-67 circuit board files to http://www.Teenix.org/HP67pcb.zip

It has the Gerber files and instructions on how to instruct a PCB manufacturer to make the files. I had the PCB files checked at PCBway and they passed inspection. They quoted $US5.00 for 5 boards plus whatever delivery option is required.

There is also a PDF document with the schematic and circuit board design details.

cheers

Tony

[Tapti]

Tony,
this is a very stupid question for sure, nevertheless:
Do I understand correctly that letting this board produced by a manufacturer means producing only the board without any electronic part on it, right ?
Beginner in this business, sorry
Stefan

[teenix]

(11-29-2021 06:15 PM)Tapti Wrote:  Tony,
this is a very stupid question for sure, nevertheless:
Do I understand correctly that letting this board produced by a manufacturer means producing only the board without any electronic part on it, right ?
Beginner in this business, sorry
Stefan

Hi Stefan,

Yes, just a bare board. I doubt it will be used much but might help someone has a badly corroded circuit board and wants to swap over the original parts.

None the less, the included 67 circuit board overlay might be useful. I'll be adding it to the Classic Notes PDF soon.

cheers

Tony

[metawops]

(11-29-2021 10:56 PM)teenix Wrote:  I'll be adding it to the Classic Notes PDF soon.

cheers

Tony

Hi Tony & sorry for this noob question: Where can this "Classic Notes PDF" be found?

I'm currently trying to repair my HP-67's card reader and am in the phase of acquiring knowledge. For example, is there some information about which cable from the read/write head and motor plugs into which socket on the card reader PCB? ?

Thanks so much & cheers
Stefan.

[teenix]

Hi Stephan,

Classic notes here...

http://teenix.org/ClassicNotes.pdf

Tony Duell's 67 drawings have the wiring and colors shown in this document...

http://www.hpcc.org/cdroms/schematics5.0...c/hp67.pdf

cheers

Tony

[metawops]

(07-11-2022 02:11 PM)teenix Wrote:  Hi Stephan,

Classic notes here...

http://teenix.org/ClassicNotes.pdf

Tony Duell's 67 drawings have the wiring and colors shown in this document...

http://www.hpcc.org/cdroms/schematics5.0...c/hp67.pdf

cheers

Tony

OH. EM. GEE.

WOW! I'm blown away from that "Classic Notes" PDF!!
I do have a 35, a 45, a 55 and a 67 (and a 97) and there's SO MUCH KNOWLEDGE in that PDF file! WOW!
Thanks SO much for all the effort!!
It'll sure help a LOT in repairing my Classics!

(Now if only I had at least one single magnetic card to test the success of my repairing attempts ... ? There are currently some on ebay here in Germany – but is 2,40 Euros a "reasonable" price for one single card?? Any other sources? ?)

Okay, back to on-topic. Attached is a photo of a part of my 67's circuit board to which the card reader is connected – do I have to worry? Is this a serious problem? Should I repair this with small wires?
   

Oh, and I have other question regarding the card reader repair – is there a "best thread" to add them or should I start a new one?

Thanks so much, guys! Happy to have you experts here!! ?

[Jeff_Birt]

(07-11-2022 03:58 PM)metawops Wrote:  Okay, back to on-topic. Attached is a photo of a part of my 67's circuit board to which the card reader is connected – do I have to worry? Is this a serious problem? Should I repair this with small wires?

That does not look bad. I would lightly scuff the area with a fiberglass pen, that should get most of the corrosion off of there. If there still looks like some corrosion in tiny crevices treat with vinegar or citric acid for 20 minutes or so then flush with water and clean with alcohol. The last step is to tin the bare copper with solder to protect it.

[teenix]

(07-11-2022 03:58 PM)metawops Wrote:  Okay, back to on-topic. Attached is a photo of a part of my 67's circuit board to which the card reader is connected – do I have to worry? Is this a serious problem? Should I repair this with small wires?

Oh, and I have other question regarding the card reader repair – is there a "best thread" to add them or should I start a new one?

If after cleaning the board traces and the solder won't take, there is circuit board lacquer in spray cans that will protect it, and you can solder through it if need be.

Stay on this thread or start a new one, it's all good

cheers

Tony

[AndiGer]

(07-11-2022 03:58 PM)metawops Wrote:  (Now if only I had at least one single magnetic card to test the success of my repairing attempts ... ? There are currently some on ebay here in Germany – but is 2,40 Euros a "reasonable" price for one single card?? Any other sources? ?)

Hi Stephan,

NO, 2.40 Euros for a single card in my eyes is NO reasonable price. This seller asks IMHO too high prices for all the HP things he's selling. (Also on ebay Kleinanzeigen.)

You are also located in Germany. If you didn't bet/buy from another source I can send you some cards. In this case PM me.
Andi

[metawops]

(07-11-2022 10:51 PM)teenix Wrote:  Stay on this thread or start a new one, it's all good

cheers

Tony

Thanks, Tony! I'll stay here, then.

HUGE thanks to AndiGer who supported me by sending a few magentic cards and silicon two fuel tube snippets. ??
I installed one on the gear axle and reassembled the reader and the HP-67 up to the point where I could do a first test. (I didn't change any capacitor, yet; should I?)
I connected the HP-67 to a lab power supply, set that to 3,7V and switched the HP-67 on.
The display is fine, the keys are fine, it calculates correctly.

Now, first question: am I allowed to use the card reader under this (lab power supply, no batteries) circumstances? I hope so, because I did insert a magnetic card. ?

Result: the card could hardly be moved through the calculator. It went in veeeery slowly, the motor made a low sound (slow rotation) and the card almost got stuck completely inside the reader. I was lucky that, after a while, it came out on the other side so I could pull it to help the motor. (The result in the display was, of course, "Error".)

Maybe the silicon tube is too thick? I measured an outer diameter to be 6.57mm which should be fine, right? (I have another tube that has an OD of 6.08mm – both measured when applied onto the axle.)

HOWEVER ... When I took everything apart again I noticed that one of the two tiiiny screws that fix the motor to the plastic chassis is missing!! ?

Here's a photo:
   

Now ... is there a chance I can get hold of one such screw? What are the exact specifications for this screw? Any hint? Is it even a real problem? Will the reader only work with the 2nd screw properly installed?

In another attempt (before I saw that the screw was missing) I connected the motor directly to the lab power supply (card reader fully assembled) and set the power supply to app. 1.8V – can I supply more voltage here?. The motor made "uneven" sounds but the card was transported quite nicely. I made a video that you can download (>80MB) here.

Off to bed now, eyes going bad, too many tiny things ... ?

Thanks a lot for any help!

Stefan.

[teenix]

(07-15-2022 09:36 PM)metawops Wrote:  Now, first question: am I allowed to use the card reader under this (lab power supply, no batteries) circumstances? I hope so, because I did insert a magnetic card. ?

Yes, as long as the supply can provide 500mA or so comfortably. CAUTION: Do not accidently reverse the power polarity and switch on or you will most likely destroy some internal parts. Some (like the sense chip) are connected direct to battery with no protection. The card motor should draw about 180mA when pulling a card.

(07-15-2022 09:36 PM)metawops Wrote:  Maybe the silicon tube is too thick? I measured an outer diameter to be 6.57mm which should be fine, right? (I have another tube that has an OD of 6.08mm – both measured when applied onto the axle.)

I'd use the smaller diameter. Also if the tube is too hard, especially on cold days, then the pressure on the card reader becomes greater and could cause damage to the mechanical parts, and also overload the motor and sense chip motor driver.

I could be wrong but I feel tubing of 1/4" or greater is slightly too large. !/4" o-rings only have a point contact on the card and probably squash up a bit and the diameter reduces a bit in use, plus in practice, there is only one o-ring in contact with the card. With tubing this effect lessens. I've used silicon tubing that feels quite soft, slightly less than 1/4" OD and it works fine in some readers but not all. With the motor removed you should be able to manually feed in a card back and forth but with not too much force - hard to quantify this though. It would be nice to dream and have an original drive wheel in mint condition to make some measurements. I am looking for o-rings with a 50 buna n rating (softer than normal) but I haven't find them in Oz yet.

(07-15-2022 09:36 PM)metawops Wrote:  In another attempt (before I saw that the screw was missing) I connected the motor directly to the lab power supply (card reader fully assembled) and set the power supply to app. 1.8V – can I supply more voltage here?.

I would avoid doing this as you will be feeding power back into the sense chip. I don't know if this will damage it and other components or not but it is not worth the risk. Unsolder the +ve wire from the motor, or unplug it from the sense board if it is the type with wire sockets fitted, then connect the motor direct to the supply for testing.

The sense chip seems to output about 2.4V when running the motor - details in Classic Notes - page 32.

cheers

Tony

[metawops]

Thanks for all the most valuable tips, teenix! Much appreciated!

However, today let's put all things screw and silicon and pressure and gummy and that aside and focus on a new problem (yay!) I observed today: When I insert a card and the first switch (MTRS) goes down (i.e. makes contact with the pad; can hear it) the motor should start, right?

Well, it doesn't.

When I push the card a little bit further in so that I feel that it has now contact with the fuel tube I put on the axle – still no motor.
When I still push the card further in (yes, not good, I know) at some point the motor actually starts (obviously too late) and the display says "Error".

Now ... is my sense board defunct? How could I test what's going on? What could cause this behaviour?
I've got a 4 channel oscilloscope here and am ready to test ... And I'm further studying your "Classic Notes", teenix, excellent source! (I'm by no means such an electronics expert like you are and don't understand everything immediately ...)

I really hope that my sense board is okay ...

[AndiGer]

Guess you have to adjust the golden forks by the screws seen in this video from Alberto:
https://www.icloud.com/sharedalbum/it-it...0C74048C74

Get the HP-97 service manual (for free) e.g. at https://literature.hpcalc.org/
and go to the card reader section.
Sorry I don't know which one's the right screw for the HP-67.
Andi

[metawops]

Thanks AndiGer, I will have a look at that HP-97 manual asap.

Meanwhile ... I took a look at the HP-67 schematics and the "Classic Notes" PDF. In a first step I wanted to see whether the first ball/switch, MTRS, that the card hits, actually does something/switches.
The process is documented on page 22 (PDF page 23) in the "Classic Notes" PDF and on the next page we see the oscilloscope diagram that includes the MTRS line.
However, I couldn't find a note where to put my probe on to get that MTRS signal so I looked into the schematics and found that pin #13 of the main logic board should be that MTRS pin, right?

Well, actually, I might be wrong here because this is what my scope says when connected to that pin and when the HP-67 is switched on (nothing else, no card action):

       

I get a ~6,6V peak every 300µs (screenshot 1). And that peak is ~5µs long (screenshot 2).
When I gently push in a card so that the first (MTRS) switch should "fire", nothing happens here.

Maybe I'm on the wrong pin?!

[teenix]

It is pin #16 from the left side to the right, looking down at the circuit board with the connector strip at the bottom. You probably counted from the right side and your scope is looking at the RCD pin which is the signal to Reset the Cathode Driver.

I'll add a diagram to the notes to explain the pin layout when I get a chance.

The contact fingers shouldn't have many problems. The small nylon balls that actuate them might wear over time, and the main circuit board sometimes doesn't get put in place properly resulting in different contact gaps in the switches, or the pins have been fiddled with, or maybe the calculator was dropped. Either way, they are a bit sensitive to proper adjustment.

The 97 service manual says to screw each contact down until it shorts with the board, then back off the screw 1/4 turn. Sometimes this doesn't always work if the pins have been warped at some stage.

If you remove the large circuit board you can see the contacts. They mate with the gold square contacts on the key circuit board when the inserted card slides against the nylon balls.

If you remove the motor, you can easily slide a card back and forth to the see how they work. There are 5 fingers, only the top three longer ones are used for card sensing.

Without cards in the slot, you can see the gaps between each contact and the housing where they are screwed to. They should all appear to have the same gap, about 1mm. If some are raised or lowered compared to others then the CRC chip may not detect the cards properly. With a small screwdriver, the screws can be used to adjust the gaps. Turn to the right (tightens the screw) to increase the gap. Don't overtighten them or you risk stripping the threads in the plastic housing.

If you decide to disassemble the mechanism to look more closely at the fingers, be really careful as those little balls and the tiny nylon roller have been known to disappear into oblivion if they fall out - it will most likely ruin your day.

If you decide the only way to fix the problem is the bend the fingers so the whole item looks perfectly flat, then try to be gentle and not crease the metal. This should be a last resort as bending things can sometimes screw up the tension in the metal fingers and make things worse. HP recommended replacing bent items, but that can't occur these days.

If you remove the plastic housing and key circuit board to get at the contacts, make sure it sits properly in the top calculator housing. If it is not fitted properly, it will rock slightly back and forward. If you screw it down like this it will warp and cause problems.

One last thing, there are wires connecting the boards together and with repeated handling the tiny wires that make up the cables can break. This will reduce the current that can flow through them and maybe upset the calculator - see Classic Notes pg 39.

Good luck

cheers

Tony

[metawops]

Okay, the good news ist: the MTRS switch works as can be seen in this little video I made.

https://www.icloud.com/iclouddrive/078a5...Cardreader

The bad news is: only very rarely the motor actually starts. Most of the time the motor doesn‘t start – despite the fact that the MTRS works every time.

Any ideas for me what to try next? Is it a mechanical or an electronics problem? How to find out? I‘m out of ideas … ?