HP-67 Card Reader became very touchy

[Hiwi]

Hi Alevin,
i remember, that i had a HP97 board with the same issue, and i replaced every capacitor with no sucess. The problem was the CRC chip. I replaced it from a donor HP97 board and it worked again.
Sometimes the solder joints are problematic, first try to resolder the CRC Chip.
And check the ribbon cable to the cardreader with a multimeter.

If you no donor board I can send you one or a CRC Chip.
Ralf

[Alevin]

Thank you all for your great advice an encouraging. I am learning quite a lot, being in mind I am an vulgar hobbyist without an electronic background.

Lets update.

To avoid uncertainty about the condition of the substituted C6 45 uF capacitor on the HP-97, as its capacity measure on the PCB was so different form the nominal one (on contrary to the others caps around), I took a breath ( be careful or you tryng are going to make things to worsen) an desoldered it.

Once isolated, C6 showed 44uF , just nominal capacity and 0,1 ESR. So it was OK. Nevertheless, I substituted it again for another new one. Curiously, with the logic PCB dissembled from the calculator, once a new C6 was soldered again, the measured capacity on the PCB went “overload” (above the measuring device maximum range). Never mind, as I am sure the cap and the soldering was ok an quick, without any overheating

In the same logic PCB dissembled, all the diodes were not conducting on inverse polarization, and they kept like this when reassembling the logic PCB on the rest of the calculator body, except the diode CR5, that shown again 1.4 K Ohms in inverse polarization.

As expected, this new C6 substitution did not solve the “only read card at low bat” problem, but at least I am sure that the C6 cap is now Ok.

So I am planning to substitute now the C4 6,8 uF cap (16 or 25 Volts on card reader PCB, as you and some other people have notified problems with it in the HP 65 67 97 card readeres. ( I can not find were is the other 2,2 uF mentioned by Hiwi).

In the way I will check and clean al the suggested components you all have mentioned.

Stay tuned.

[AndiGer]

(10-30-2023 08:19 PM)Alevin Wrote:  So I am planning to substitute now the C4 6,8 uF cap (16 or 25 Volts on card reader PCB, as you and some other people have notified problems with it in the HP 65 67 97 card readeres. ( I can not find were is the other 2,2 uF mentioned by Hiwi).

Surely Hiwi meant C3 on the card reader PCB - 3.3 uF.
6.8 uF is C4 there.

Keep us posted, good luck
Andi

[Alevin]

Hi, my friends

I am proceeding with a lot of cautions when going around the card reader, as I feel there is a single subtle issue that causes the constant error message when reading cards, except at low battery voltage.

As all the other functionalities work nice, and even the card read /write well al low voltage, I am reluctant to start touching every possible button to play with, since it may produce further unfitting the electro-mechanical assembly.

But I have discovered a surprising fact.

I have found that in my reader PCB there is a C3 capacitor, as in the figure 4-26 of the HP-97 service manual (1982 and 1976 version), reported to be 3.3 uF. I also assume that this one corresponds to the 3.3 uF cap indicated in pp 36 of Tony Nixon “Notes on HP’s Classic Calculators” in relation to HP-65 HP-67 card readers, that is located close to the motor, and can be seen in between the CRD motor poles in all HP-65 HP-67´s.


It seems that in the HP-97 most of the models this 3.3 uF cap has been located in the CRD PCB instead. Indeed in the Hp-97 service manual (1982 version), neither the Figure 6-3. Card Reader Exploded View, nor the corresponding Table 6-4 Card Reader Assembly (A3) Replaceable Parts, shows any cap between the motor poles.

But in seems, that in some other (¿very early?) versions, the C3 was not in the PCB, but close to the CRD motor poles, as in HP-65 HP-67. Look at the pics describing the HP-97 Card Reader Repair by Peter M Geiser; https://www.keesvandersanden.nl/calculat...Geiser.php

NO C3 cap is seen in pic 4 , showing the CRD PCB

But in last pic, a cap is seen in between the motor poles.

Now here it comes the surprise…

As it is shown in the attached pic (look at the two blue arrows), in my Hp-97, apart from the C3 3.3 uF cap in the CRD PCB, there is another cap (quite similar to C3) in between the motor poles, as in found in HP-65, HP-67 calculators.

I wander if this cap is duplicated!!

If so, it could be the explained because of previous owner, who change the CRD gummy wheel for O-rings, may introduced it replicating/copying the similar fashion to the Hp-65 Hp-67, unadvertised that it was alredy in the PCB. Against this conjeture: the motor cap has the same old coloured style, it seems exactly the same, than the C3 on PCB, suppoused original.

Was the Hp-97 serviced, and being C3 dead, another one was inserted in the motor? repair simpler than desolder and recap?

I have not yet removed any, but on the PCB the ESR measured on both seems OK (0,7-0,9 Ohms).

What do you think?

Is this the same in other HP-97´s.?

Will this presumable duplication negatively influencing the reading?

Regards

[teenix]

I'm guessing the MI input on the sense chip is for Motor Inhibit.

If so, the 2nd 3u3 capacitor is part of a motor inhibit circuit. I guess the motor turns on briefly at switch on or switch off for the 97 and this circuit addition stops that.

It is not used in the 65/67, but is in the 41 card reader module.

cheers

Tony

[Hiwi]

Hi,
the marked capacitor on the PCB is the 3.3uF, the blue on the right is the 6.8uf
The big red ones are 22uf. They are in series with the read/wright coils. if the ESR is too high, or the value is not correct the signal may be too low or cut off.

I replace them always complete when fixing the reader.
C3 and C4 are connected to ground and what is their task?
They should stabilize Vss and VCC and supress ripple! Nothing else. So they are not that critical regarding the value.

Resolder them or change them. They are cheap. But new ones do not have always better ESR.

Don't bother to much with the ESR and values, as I have already told. I take for C3 and C4 values I have on hand, 4.7 or 10 worked for me in any case.

Try to get high qualtity tantalums from vishay or Kemet.

If you take the PCB apart remove the motor cables and look for the head cables, as they come off sometimes.

And cut the legs from the tantalums as short as you can. And resolder them with more heat, so that there is good contact under and on top of the PCB. The trough-holes of the pcb may be faulty. I do not use leadfree solder.

The capacitor on the motor (connected directly on the motor) is a 3.3uf as well. It is not critical. I replace it with something i have on hand. And this could be a 4.7 even an small electrolyt capacitor is sufficient.

Some people solder an extra tanatalum from pin 20 of the sense chip to ground. PIN 20 is VBB.

If you take off the PCB, clean the contacts thoroughly with IPA. The head as well, dry clean afterwards.

And test the contacts, may be the headswitch may be faulty:

Connect a multimeter to TP8 and insert a card by hand and test TP9,TP10 and TP11.

TP9 should turn on first then TP10 (if no writeprotected card is inserted) then TP11.
This is a very common fault! You can adjust this with the 3 screws. Remember the position, take a picture before.

And don't put to much tension to the screws of the PCB. In Germany we say: "Nach fest kommt ab" :-)

And did you measure the resistance of the head coils? Blue-Orange and Red-Yellow, schould be the same in both measurements.

Have you resoldered the CRC Chip on the main PCB?

Ok, any more does not occur to me now. :-)

Ralf

[Hiwi]

(11-05-2023 07:09 PM)Alevin Wrote:  Was the Hp-97 serviced, and being C3 dead, another one was inserted in the motor? repair simpler than desolder and recap?

No, this is a common design rule to eliminate a so called 'brush fire' of brushed motors. (FCC)

This cap should be placed as close as possible to the brushes.

The motor cables work like a an antenna for the HF/LF signal, which can disturb electronics inside and outside the calculator. The cap shorts these electrical interferences.

I have never seen any cardreader without this cap (HP41/HP67/HP97) Same as with printer motors in the HP97 or the HP82143/162

Ralf

[Hiwi]

(11-05-2023 07:09 PM)Alevin Wrote:  NO C3 cap is seen in pic 4 , showing the CRD PCB

Yes but if you look closer you can see, that there was a cap, but broken off. Parts of the legs are still in place in the through-holes.

If this cap is missing and the cardreader works than this supports what I said: the cap is not that important.

At the botton of kees page there is another link for a cardreader repair and look C3 and the motor cap are both present:

https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=180

What is primarily important is the schematic of the cardreader in the service manual.


Ralf

[teenix]

C3 delays the turning off of Q1 when the calculator is switched off. This may prevent spurious motor running with power changes. This might happen sometimes but not others, and maybe why the engineers added it. This is of course dependent on the MI input on the sense chip being for Motor Inhibit, otherwise I have no idea :-)

The ribbon cable in the image on post #44 looks like care needs to be taken when removing or inserting, being creased like that. The ribbon connectors will crack easily in this situation. They can be repaired with solder but care from then on will still be required. I haven't been able to find a suitable replacement for these. Aside from lengthwise, 0.1" pitch spacing doesn't seem to be the norm for cables like this these days.

cheers

Tony

[Alevin]

Great all you expertise advise that will be helpfull for so many people interested in saving this magificinet apparatus. I plan to dedicate some more efforts at Christams time to try to solve issue.

[Hiwi]

Good luck and test the ribbon cable.
Ralf