The Museum of HP Calculators

HP Forum Archive 20

[ Return to Index | Top of Index ]

Hp-42s display problem
Message #1 Posted by aj04062 on 23 Feb 2011, 10:29 p.m.

I'm looking for confirmation on the root cause on a display failure on a 42 I just acquired.

Half of pixels in one ROW are out. Does it make sense that this would be a bad Zebra connection? Unless more drop out I think it might be foolish to open this up to repair.

Agree?

Thanks for the feedback!


      
Re: Hp-42s display problem
Message #2 Posted by Randy on 24 Feb 2011, 12:30 p.m.,
in response to message #1 by aj04062

Twisting the case slightly should prove/disprove the theory.

I have seen cracked LCD's along one corner, typically the top left or right that exhibit that behavior. The crack is not visible from the front, only from the back when the zebra is removed.

The missing row - which side and which row? From that I can figure out where that element terminates on the LCD.

            
Re: Hp-42s display problem
Message #3 Posted by aj04062 on 24 Feb 2011, 9:34 p.m.,
in response to message #2 by Randy

Here is a picture

                  
Re: Hp-42s display problem
Message #4 Posted by Marcus von Cube, Germany on 25 Feb 2011, 2:20 a.m.,
in response to message #3 by aj04062

That's probably a failed driver IC.

                        
Re: Hp-42s display problem
Message #5 Posted by aj04062 on 25 Feb 2011, 7:01 a.m.,
in response to message #4 by Marcus von Cube, Germany

If that's the case, is a replacement only available from another 42 or is the 17BII have the same IC?

                              
Re: Hp-42s display problem
Message #6 Posted by Walter B on 25 Feb 2011, 8:36 a.m.,
in response to message #5 by aj04062

Please look at this:

IMHO there's not much on the pcb you can swap.

                  
Re: Hp-42s display problem
Message #7 Posted by Randy on 25 Feb 2011, 11:42 a.m.,
in response to message #3 by aj04062

All 16 rows on the left side terminate along the top left edge of the LCD. The row in question would be right below the top right twist tab as seen from the back.

If it isn't a contact issue, it is either a failed driver row on the IC or a failed lead frame bond on the die. FWIW, I've found that mechanical failures of the lead frame out-number electrical die failures about ten to one. That said, that element lands pretty much dead center on the right edge of the die so I'd be inclined to think it is electrical, not mechanical.

                        
Re: Hp-42s display problem
Message #8 Posted by aj04062 on 26 Feb 2011, 10:03 p.m.,
in response to message #7 by Randy

Well, I pulled the calculator apart because as I twisted, another half row blinked on and off. I deduced, it was probably a bad connection in need of repair.

Well, I do believe it is. When I got it apart I immediately noticed green corrosion in areas near the zebra.

Well I cleaned as delicate as I could with warm water, vinegar and a q-tip. I think there are 2-3 traces that need repair. YES the corrosion is this bad, It reminds me of a 65 I repaired that had a completely exploded battery.

Anyone have a good source of VERY FINE trace repair? I think the conductive trace pen is the only way to go here, agreed?

                              
Re: Hp-42s display problem
Message #9 Posted by Wanderley Navarro on 27 Feb 2011, 12:06 a.m.,
in response to message #8 by aj04062

Maybe this will solve.

But an advise from Randy would be highly appreciated.

                                    
Re: Hp-42s display problem
Message #10 Posted by aj04062 on 27 Feb 2011, 8:36 a.m.,
in response to message #9 by Wanderley Navarro

I Purchased a Micro Tip Silver Trace Pen last night from Cicuitworks. My only concern is that the tip may be too large to work with (.8mm)

The traces are about half that width I think.

I'll give it a try. I want to use it on the 65 with the exploded battery anyways.


[ Return to Index | Top of Index ]

Go back to the main exhibit hall