HP67 repair - help identify capacitors

[husmus]

Can someone help identify the capacitors in my HP67? I've done the gummy wheel repair and now I get the 'error' message as it pulls the card through. I've attached a photo of my HP67.

The HP97 document talks about...
C1 2.2uF Vgg voltage doubler
C3 2.2uF Vgg voltage doubler
C2 68uF
C4 22uF Vss smoothing
C5 3900pF
C6 47uF
C? ??uF across motor

[teenix]

If you download the zip file for my HP-67 circuit board design, you will see a file called "HP67olay.pdf".

If you open this, you will see the locations of the capacitors.

The one I would consider changing is the battery supply tantalum capacitor marked as 47uF as it has been linked to faulty card reads. This is a polarity sensitive component so they have to installed the correct way or you will see a mini fireworks display when you apply power, and it will smell bad too.

cheers

Tony

[isanchez]

Dear Tony,

thanks for the information. I am repairing an HP67 with the same problem.
In a first sought I realised the card reader header module was loose. I glued it back, but I suppose that the "error" message can be in a misalignment of the header. I find this could very sensitive to a good alignment, am I right? I am willing now to replace the whole part (plastic + header).

If I do not succeed, I shall try the capacitor replacement. A basic simple question: what do you recommend for the voltage of the 47uF capacitor? sorry for this question but I am not familiar with this electronics at all.

Thanks in advance and kind regards.

Ignacio

[teenix]

I assume you mean the magnetic head came loose, so yes it would have to be aligned the same way as when it was manufactured, which includes its vertical position in the plastic housing so that it will have the correct pressure against the card as it passes over.

The capacitor is connected across the battery which is about 3.75 volts, so 10 or 16 volt rating should do. The higher the voltage may mean a larger sized part.

cheers

Tony

(07-06-2023 07:27 AM)isanchez Wrote:  Dear Tony,

thanks for the information. I am repairing an HP67 with the same problem.
In a first sought I realised the card reader header module was loose. I glued it back, but I suppose that the "error" message can be in a misalignment of the header. I find this could very sensitive to a good alignment, am I right? I am willing now to replace the whole part (plastic + header).

If I do not succeed, I shall try the capacitor replacement. A basic simple question: what do you recommend for the voltage of the 47uF capacitor? sorry for this question but I am not familiar with this electronics at all.

Thanks in advance and kind regards.

Ignacio

[husmus]

Tony, Thanks so much for your help and documentation !!!

(07-05-2023 10:36 PM)teenix Wrote:  If you download the zip file for my HP-67 circuit board design, you will see a file called "HP67olay.pdf".

If you open this, you will see the locations of the capacitors.

The one I would consider changing is the battery supply tantalum capacitor marked as 47uF as it has been linked to faulty card reads. This is a polarity sensitive component so they have to installed the correct way or you will see a mini fireworks display when you apply power, and it will smell bad too.

cheers

Tony

[John Garza (3665)]

While you are in there, may be worthwhile to replace all the capacitors as they will eventually fail. In servicing vintage radios, the popular term is 're-capping'. Just good preventive maintenance.

-J

[Hiwi]

Hi,
i have repaired many HP-67, many :-)
I do not recommend to replace all caps without understanding their function.

If you have test equipment you can measure the ripple.

Replace the big yellow cap on the mainboard, it is a 47uF tantalum, then the brown one, it is 22uF.

If you have a cap tester and see a great Vloss, replace it, if it is under 1%, put it back.

Use only tantalum caps.

But in most cases the caps on the cardreader PCB are the problem. There are different versions.
On your board there are axial tanatalums 2,2uf, i bit hard to get and expensive.
The cap across the motor never fails :-)

Do not buy NOS from ebay, they are often 20+ years old. Digikey or Reichelt have them in stock.

And try following:
1.) Write a card with some code.
Try to read in another cardreader (67,97 or HP41)
Does it read sucessful? => there is a great chance, that the problems are the caps.

2.) Supply a voltage so that the battery indicator comes up, at about 3.2 volts.
Try to read a card. If it works => in most cases cap problem.

Does not? Could be a greater problem with the signal controller (does the card stop correct? if not may be cleaning of the contacts may help)
or the CRC Controller on the mainboard, but this happens not often.

Did you check the speed? On your PCB, there is no poti to adjust the speed, so it is fixed.The
service manual advices you to change a resistor on the pcb. But do not replace anything here.

If you have replaced the roller the diameter may not be exact and correct.
The white (on early HP67s, otherwise black) axle (for the spur gear) is not straight, it is slightly bend so you have to adjust the
pressure the card is pressed on the head. This has influence on the speed as well.

Try to play around a bit.

If you can measure the current while reading, adjust the axle so that the meter is reading 200mah at 3.8 volt.
Ralf

[teenix]

(07-11-2023 10:12 AM)Hiwi Wrote:  Hi,
Replace the big yellow cap on the mainboard, it is a 47uF tantalum, then the brown one, it is 22uF.

There could be other cap colors installed on different model releases, but most I have seen are the other way around as per attached image. The brown 47uF is across the switched battery supply which on the circuit board design, is where marked.

cheers

Tony

[isanchez]

Thanks a lot to all of you for your helpful information.

I finally repaired the card reader replacing the magnetic reader module.

Now works fine.

Regards

Ignacio