HP-65 and HP-67 card reader how to test the amplifier ?

[albertofenini]

Hello everyone,

I have three card readers, all from HP-67 units that apparently don't works

All the CPU boards units when coupled with a working card reader can read and write
which in way proves that the 1820-1751 and the ACT chips work as they should.

All of the card readers have the plug-in connectors rather than the soldered cables,
and I'm thinking of removing these connectors and solder the head and motor cables
to provide a better and more reliable connection

However, prior to do so I was wondering if there is any technique that can help me in
check that the 1826-0322 sense amplifier (BTW all of three have this version) works

Thanks for help and take care

card readers pictures here : HP-65 Card readers

[teenix]

(10-08-2022 07:00 PM)albertofenini Wrote:  Hello everyone,

I have three card readers, all from HP-67 units that apparently don't works

All the CPU boards units when coupled with a working card reader can read and write
which in way proves that the 1820-1751 and the ACT chips work as they should.

All of the card readers have the plug-in connectors rather than the soldered cables,
and I'm thinking of removing these connectors and solder the head and motor cables
to provide a better and more reliable connection

However, prior to do so I was wondering if there is any technique that can help me in
check that the 1826-0322 sense amplifier (BTW all of three have this version) works

Thanks for help and take care

card readers pictures here : HP-65 Card readers

The guess the only practical way is to use an oscilloscope and monitor signals into the IC and signals out at the PCB pins.

Also, use a known working motor for testing and consider replacing the caps.

Soldering the wires directly would be a good thing if you suspect the single connectors are corroded. You may have to trim and strip insulation from the wire ends because new solder may not take to them.

cheers

Tony

[albertofenini]

This actually what I did, Keyboard PCB and motor are trustworthy
I have tried all the three CPU boards with this set and a working card reader

Then I have combined each CPU with it's own card reader (head and electronic)
keeping the known working keyboard set

I'll buy some new caps, these should be : 22microF (qty 2) for the head,
3,3 microF for the motor and 6.8 microF for for pins 16 and 18 of the Sense Amplifier, what voltage is suggested ? (Tantalium right ?)

I have updated the photo book with the values measured for each head

HP-67 Card readers updated

I have a question, if I keep the head disconnected from the card reader pcb and I
want to check the signals when a card goes thru, to which cables from the head should I connect the
probe ?

I think that the connectors are providing a connection (the motor runs
which means it gets power thru the connectors) but with micro currents the connectors could cause a loss of intensity
and the sense amplifier could suffer from this

However, I would like to build a sense tester since this is often the responsible of a non working card reader

Thanks for any hint, take care !!!

[albertofenini]

Also, I have noted that 6,8 microF is a difficult value to find,
Can it be replaced with something different ?
Thanks and take care !

[teenix]

(10-08-2022 09:39 PM)albertofenini Wrote:  I'll buy some new caps, these should be : 22microF (qty 2) for the head,
3,3 microF for the motor and 6.8 microF for for pins 16 and 18 of the Sense Amplifier, what voltage is suggested ? (Tantalium right ?)

I have a question, if I keep the head disconnected from the card reader pcb and I
want to check the signals when a card goes thru, to which cables from the head should I connect the probe ?

Also, I have noted that 6,8 microF is a difficult value to find,
Can it be replaced with something different ?

10, 16 or 25V Tantalum should suffice.

If you look at Tony Duels circuit for the 67, the colors are marked.

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

The 6.8uF is fairly common, and is available from the worldwide distributors like Mouser, and I see them listed in local hobby suppliers and on the Bay of All. If it is not feasible to get one, try a 10uF.

cheers

Tony

[albertofenini]

Hi everyone,

this was my setup :

the head was disconnected from the card reader except for the ground cable which was connected

the head cables red and yellow connected to the scope : positive of the scope to the red cable
and ground (negative of the probe) to the yellow

the scope settings are as follow :200micro Seconds and 500milliVolts

However, when a card goes thru nothing come on the screen,

What I'm doing wrong ?

The idea is to check what comes out from the magnetic head when a card is read

Updated photos here : HP-65 and HP.67 card reader photo album updated

[teenix]

The head signals should be about +/-100mV and can be read when the sense chip is connected with a scope probe connected to HAC or HBC.

The scope trace is on page 31 of the Classic Notes

cheers

Tony

[albertofenini]

Thanks Tony,

that means that if not connected to the sense amplifier there is nothing to
measure straight out of the magnetic head, right ?

I'll try and let you know

Take care everyone !