HP-65 - 1604S01786 - Display faulty or Drivers faulty ?

[albertofenini]

Hi everyone
this is a unit we acquired from a member of the forum, it's a Spanish version of the HP-65.
It had the first block of the display faulty, or at least so it seemed.
Looking at the pictures it can be seen that also the second block is faintly lit when the unit was turned on.
At first we focused on the 1st block.
We replaced the 1st block twice,we may have used a left over of a repair the first time,
but we used a better spare part the second time, however as it gets better yet is not fixed.
We used some spare parts recovered from and old HP-45, we can't remember if and how well these were working.
What do you think, is it more on the display side or on the anode and cathode drivers side ?
We rebuilt the card reader and the unit reads and write quite well
We didn't rebuild the clutch but it has to be done ....
Cleaning of keys will be done at the end, we wanted to fix the hard stuff first....
Thanks for any idea you would like to share with us ....
Take care !!!
Pictures can be seen here : HP-65 1604S01786 - Display faulty or Drivers faulty

[teenix]

The LEDs look like some I have seen where the segments appear to be faulty and have degraded over time. They light in small areas rather than the full segment.

The partially lit display I would think, needs to be checked with a scope. The cathode driver for that digit might be faulty keeping the digit partially on and ghosting from the other lit digits.

cheers

Tony

[albertofenini]

Hi Tony
will try to get some spare LEDs that we have seen working for sure for the first block, and see if it improves,
for the second block, the one that has a faint partially lit digit, what and where should we check with the scope ?
What should we expect ?
Thanks !!!!!

[teenix]

(02-17-2020 12:01 AM)albertofenini Wrote:  Hi Tony
will try to get some spare LEDs that we have seen working for sure for the first block, and see if it improves,
for the second block, the one that has a faint partially lit digit, what and where should we check with the scope ?
What should we expect ?
Thanks !!!!!

The likely way the segments can light like that is if the cathode drive output for that digit is playing up. It should only have a LO signal on it when the digit is supposed to be on. If the scope shows flickering or noise on that output, it would suggest it is faulty.

cheers

Tony

[albertofenini]

Hi everyone, display has been fixed !
We sourced two blocks from another HP45 and from the same unit we also recovered and used the inductances
The display now works as new
Next steps will be the clutch as the unit reads and writes but is too noisy
Then we will do the cosmetics
On another post we have shown an alternative way to flatten the label so this unit will receive the original Spanish label
Pictures added here : HP-65 1604S017686 -Faulty display

[Moggul]

Congratulations Alberto and son! I knew you would make it, only I thought it would take you a bit longer

[albertofenini]

Hi Moggul
We still have to rebuild the clutch and do some tests
and all the cosmetic work but it will come out as new !

[teenix]

I would have loved to see the scope traces of that display before and after. It is always a source of curiosity why parts that don't appear to play a part in a problem turn out to be the culprit.

Well done.

cheers

Tony

[albertofenini]

Sorry for that Tony,

we replaced the first block because it was almos clear that the original was a defective block and
the spares used until now were possibly old and damaged themselves.

So it was and when this worked out we
decided to give a try with the second block and to our surprise it worked out.

We can always measure the value now, but to what and where should we measure ?

At the cathode driver ? That was probably digit number 9, counting digit 15 the far most left
which means we should put the probe at pin 1 of the cathode driver, is this correct ?

Let us know, and we will do it
take care !!

[EDIT] sorry, I meant digit number 8, since the number 15 is the first - sign

[teenix]

hi Alberto,

No need, just curious, thanks :-)

cheers

Tony

[albertofenini]

We will be happy to do it
And we are curious too
Is the pin we mentioned the right one to measure ?
Let us know
Take care !

[teenix]

(02-18-2020 09:57 PM)albertofenini Wrote:  We will be happy to do it
And we are curious too
Is the pin we mentioned the right one to measure ?
Let us know
Take care !

Hi Alberto,

Probably not much value now because the fault has been removed. I guess there is no point now risking damage to a newly working calculator.

It is hard too see why a digit mid display would be ghosting due to a faulty display module. The only thing I can think of is one or more LED segments went faulty and perhaps lost some of their diode properties causing small leakage currents to flow.

cheers

Tony