HP-67 - 1705S02263 - Full Repair Advice Requested (was HP-67 - strange behavior)

[albertofenini]

Hi everyone, as said we have split in two the original thread.

This is what was left on the bench after received the donor CPU board for the HP-67 1612A03018 :
- the broken logic board
- two card readers HP-65 syle that didn't work with the HP-67 1612A03018
- one keyboard pcb missing the transistor between anode and cathode driver
- a case with a very much deteriorated facelift

The broken logic board : We have found good Phi1 and Phi2 on the ACT, the CRC and the ROM0.
However, the side of the ROM0 that handles the segments of the display is dead.
We will measure if there is any LED activity as suggested from Tony in the old previous thread

The Keyboard PCB : we need to find a replacement for the M624 3-393 any idea on that ?
Also on this we will need to replace the RCA chip as two segments in each of the leds are not working

The Card reader : since it didn't work with the HP-67 1612A03018 we are expeting it will not
work with this either, but who knows ...

The facelift : we heard of a vinyl layout that can be put over original layout, but we can0t remember where, guess was in the Panamatik website

Most urgent is the replacement for the broken transistor, we will greatly appreciate any advise on that

Pictures here : HP-67 1705S02263

[teenix]

(10-20-2019 01:55 PM)albertofenini Wrote:  The Keyboard PCB : we need to find a replacement for the M624 3-393 any idea on that ?

Also on this we will need to replace the RCA chip as two segments in each of the leds are not working

I'm not sure of the transistor specs or what type the transistor you refer to in the circuit(PNP or NPN), but maybe a BC337 NPN, and BC327 PNP or similar, 2N2222A, PN100, 2N3906 etc.

If you have a mutimeter with a transistor function you might be able to find gain (hFE) details etc and find a similar item.

Are the chip solder connections and pcb tracks from chip to leds ok for these segments.

cheers

Tony

[AndiGer]

Take a look there:
https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=177507
Did you replace with 2N3330 back then?
Would be of interest (for you and us :-))
Andi

[albertofenini]

Hi Andi,
no we didn't, this is how looks the display (this is supposed to be 0.00) when a good working CPU is loaded

The segments not working are C and F, which are driven by the RCA chip and not by the transistors.
Looking at the schematics, the four transistors (three on the back and one in front) should drive
the G segment, which in this case works, look at the next picture which is supposed to be a list of 8

Will replace the RCA and see what happens, still we need to repair this logic board.

[teenix]

(10-28-2019 10:39 AM)albertofenini Wrote:  Hi Andi,
no we didn't, this is how looks the display (this is supposed to be 0.00) when a good working CPU is loaded
The segments not working are C and F, which are driven by the RCA chip and not by the transistors.
Looking at the schematics, the four transistors (three on the back and one in front) should drive
the G segment, which in this case works, look at the next picture which is supposed to be a list of 8
Will replace the RCA and see what happens, still we need to repair this logic board.

The transistors drive the sign G segments for the mantissa and the exponent. This is because the cathode driver only has 14 outputs to drive 15 digits. The other segments for these digits are unused and in the HP-97 display there are actually no LEDs for those unused segments only the G's.

You should be able to see the C and F segments go logic high on CPU keyboard connector pins 17(F) and 20(C) if they are to be lit (say when a zero is displayed).

If not ROM 0 may be the culprit or there are open PCB tracks from pins 2(F) and 4(C) to the CPU keyboard connector.

Otherwise the fault is circuit tracks to the anode driver input pins 4(C) and 12(F), or the outputs 6(C) and 11(F) to the LED displays. If these are sound, then the anode driver would seem to be faulty.

The connections between the CPU and keyboard could also be faulty.

Not sure what problem it could cause, but the 8 x 24K SIP resistor package, which normally pulls the LED outputs from ROM 0 to logic 0, might have open circuit resistors on the C and F segments.

cheers

Tony

[albertofenini]

ciao Tony,
consider that this is what we get with a fully working CPU board taken from another unit,
this particular calculator is to be totally repaired, the CPU board is only partially working
and so is the card reader.
Considering that to get that display we used a working CPU board I think the culprit is
the RCA for segment C and F and of course the transistor which is totally missing because
it broke off.
We will replace the RCA and will post results
Then once the keyboard and the display is stable we will try to repair the logic board,
which is the one that only makes a flash unless we keep a key pressed before to turn it on
Take care and thanks for all the tips !