HP65 Extreme Makeover S/N 1333S07557 - Advice requested

[albertofenini]

Hello everyone,
we received an HP65 (another one, we know ...) that we are in the process of restore completely,
in the next post we will attach some pictures, we have however just began the process of
stripping down the unit.

It is working, except of course for the card reader, but the second digit is dimmed,
it lights up correctly, but it is very faint.
What do you suggest to check :
the five led component
the inductance behind the leds
or it could be a anode/cathode driver problem ?
thanks so much for any advice you would like to share with us !
   

[albertofenini]

some pictures ...

   
   
   
   
   

more in the next post ...

[albertofenini]

... more pictures ...

   
   
   
   
   

more in the next post ...

[albertofenini]

... more pictures ...

   
   
   

so far, keyboard pcb, and battery compartment parts have been cleaned with water and vinegar
card reader pinch roller been replaced (not tested yet ...)
keys washed and polished one by one
led cover polished

we will spray with matte finish the keyboard frame and remove the back label over the weekend
together with the silver trim finish which has to be restored. Also the front label needs attention.

However, we need to fix the led issue ...

thanks for help !!!

[[kby]]

No advice but i’ll Be interested in what you find out and others say. I have a -65 with a (perhaps only vaguely) related issue: Works fine except for a faint ghosting of some segments in LED 3 (I think—maybe 4) if they are lit in LED 8-kby

[teenix]

(05-22-2019 09:30 PM)albertofenini Wrote:  It is working, except of course for the card reader, but the second digit is dimmed,

Hi Alberto,

I would suspect the cathode driver. The 2nd digit should be pin 7 of the cathode chip. It could also be a dry solder joint on this pin or the corresponding common cathode pin on the LED display, or a dodgy PCB trace between the two.

cheers

Tony

[teenix]

(05-22-2019 10:06 PM)[kby] Wrote:  No advice but i’ll Be interested in what you find out and others say. I have a -65 with a (perhaps only vaguely) related issue: Works fine except for a faint ghosting of some segments in LED 3 (I think—maybe 4) if they are lit in LED 8-kby

The energy in the inductor for each LED segment has to be completely discharged before the cathode driver is sequenced to the next LED digit. If this doesn't happen, then the remaining inductor energy is passed to the next LED and the 'bleeding' that you see takes place. This means the timing between the ARC, anode and cathode drivers has to be quite precise.

Why it happens only on one or two digits might suggest a higher than normal resistance for the inductor discharge path. This is normally from the inductor, through the LED segment, out through the LED digit common cathode pin and into the relevant cathode driver and then to ground.

Look for dirty looking solder joints or corrosion around the display and the drivers. It could be the corresponding transistors inside the cathode driver are showing their age and are not passing the inductor current as well as they should.

cheers

Tony

[Geoff Quickfall]

Had a similar problem. Bad LED block.

Try swapping blocks (desolder etc). Then go after the more complicated stuff.

[albertofenini]

Well, guys no way to fix ... until now

we swapped the led block with a working one : no improvements
we swapped the cathode and anode driver : no improvements
we changed the inductors (both) : no improvements
we even changed the small capacitor on the upper left : no improvements
we cleaned the logic board with water and vinegar : no improvements

We noticed this : we have put this logic board in another HP65 and everything works well
We took a logic board from another unit (working) and when put in this chassis it doesn't even turns on

Meanwhile we proceeded with the restoration, definetely not our day .... the keyboard plate was coming out so nice (look at the picture)
when giving the FINAL touch we put by mistake too much matte finish and the result was ugly, trying to clean it up made things even worst
as you notice you can still find evidence around the key number 8, and where the card is put at rest
However, all in all (and considering the damage we made) is coming out nicely.

We tested the card reader and reads OK, but doesn't write, we will take care of that later.

We need your help with the display issue ... any idea please ???

   
   
   
   
   

[[kby]]

Thanks very much for the hints, Tony. Sounds like it’s going to be something that needs more time from me; hopefully later this summer…-kby

(05-22-2019 11:59 PM)teenix Wrote:  

(05-22-2019 10:06 PM)[kby] Wrote:  No advice but i’ll Be interested in what you find out and others say. I have a -65 with a (perhaps only vaguely) related issue: Works fine except for a faint ghosting of some segments in LED 3 (I think—maybe 4) if they are lit in LED 8-kby

The energy in the inductor for each LED segment has to be completely discharged before the cathode driver is sequenced to the next LED digit. If this doesn't happen, then the remaining inductor energy is passed to the next LED and the 'bleeding' that you see takes place. This means the timing between the ARC, anode and cathode drivers has to be quite precise.

Why it happens only on one or two digits might suggest a higher than normal resistance for the inductor discharge path. This is normally from the inductor, through the LED segment, out through the LED digit common cathode pin and into the relevant cathode driver and then to ground.

Look for dirty looking solder joints or corrosion around the display and the drivers. It could be the corresponding transistors inside the cathode driver are showing their age and are not passing the inductor current as well as they should.

cheers

Tony