HP-65 goes on hold after reading a card

[teenix]

(11-16-2020 04:08 PM)albertofenini Wrote:  From what I read this is what I understand :
When a card is inserted the MTR switch is closed and the CRC in the hybrid (?) gives power to the motor thru the Sense Amplifier.
No, the CRC tells the sense chip to power on the motor via the [Motor] pin which goes LO for Motor=ON, HI for motor=OFF
The sense chip gets motor power directly from the battery, but the sense chip has a constant current circuit that controls the motor speed.
The external resistor sets the current for this circuit

Let's keep it simple with focus on the tracks, forget about HDS and WPS for now and suppose we are reading a card

The calculator can keep maximum 100 steps @ 6 bit each one, is this why a card can contain 600 bit at maximum?
Yes, it only needs to store 600 bits

Now the head: it has two channels, A and B but for each channel it sends back signals on three pins : HAC, HA, CA and HBC, HB, CB
Also HAC and CA are connected together and both benefit from a 22microF condenser and the same is for HBC and CB

What's the difference between HAC and CA or HBC and CB ?
What's the difference between HA and CA or HB and CB?
See Below

Is there a way to test a head ? Anyone knows what the inductance values should be ?
Only that it should have a small resistance. I don't know inductance

Than I have understood that the Sense Amplifier works these signals what is into RA and RB
These two combined have all the information including this auto clock feature
These are sent to the Hybrid to store the program steps, well the corresponding bits
See HP Journal 1974 Page 4

Is it true that when reading : HAC, HA and CA are converted in RA and HBC, HB and CB are converted in RB ?
Yes

Now, when we record : WPS recognize that the card can be written, and suppose WE is coherent with this situation, so it's ok to write.
WE goes HI for a write, LO for a read. If WPS goes LO before HDS then the CRC decides the card is not write protected

I have understood that the the Program Steps (bits) are coded into WA and WB and then the sense amplifier send these to the head
thru HAC, HA, CA and HBC, HB HC this time writing magnetizing the card
Yes

(BTW what all these acronyms stand for ?)

Guessing, but seems logical
HA HB= Head A Head B
HAC HBC = Head A Capacitor, Head B Capacitor
CA CB = CapacitorA, Capacitor C


How far am I from understand the basics f the card reader ?
Pretty good :-)

On some schemes there is also a CRT/P signal (on the card reader connector with the logic board is just below the WE pin)
Is this important ?
Not sure, I haven't seen this

Having said this, if I'm not wrong this is the flow of data and the sequence :
when reading :from the head, to the sense, from the sense to the memory
when writing : from the memory to the sense and from the sense to the head
Correct

if the WA or the WB are dirty where the heck is this happening and why ?
WA WB come from the CRC chip in the hybrid. It (or the sense chip) could be faulty if the tracks between the CPU board and sense chip are ok

Should that happen before the Sense ?
Or inside the Sense because it is responsible for taking the information from the Hybrid and coding into WA and WB ?
You could disconnect the card reader connector and measure WA WB when writing a card

I think the flow is very important to find out what and where something can possibly go wrong

I may have written many non-sense, I'm sorry for that but it's fascinating how this works
All good, see the HP Journal 1974 Page 4 onwards

Thanks for help and take care !!

cheers

Tony