HP-67 Card Reader became very touchy

[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