HP 33E Repair Advice

[kusmi]

I just acquired an nice looking HP 33E. It was sold "for parts" because the display had some troubles (segments not lighting up).

After some light twisting of the case (I guess this is the solderless version) - I got all LED components lighting up again, so the LED module seems to be working. Keys are working fine and it seems fully functional (RUN and PRGM mode). The battery door is broken a bit, but still closes.

But I have two problems and would like to seek some advice - before I try to open this little puppy.

1. Whenever a digit is shown, the top-most and top-right segment is always "ON", so all 1s appear as 7s, etc (see attached images, the first shows the display when I enter 1111111111, the second shows the number -1234567890). Those additional two segments are only ON when the actual digit is displayed - if the digit is OFF, all segments are OFF.
2. I see some greenish stuff on the battery contacts - I guess this is copper hydroxide. It is not much, but I don't know if the former owner has just briefly removed some of it (so there could be more inside).
   

What do you think regarding 1.) is this something which could be repaired by just opening the calculator and cleaning some contacts or does this look like a IC/circuit problem?

And regarding 2.) what is your recommended method to remove copper hydroxide? Just brush it off or are there some recommended chemicals? I guess for the battery compartment I could clean it more aggressively than on the circuit board...

[d b]

It sure sounds like bleeding electricity across contacts is a possibility. Since you see the dreaded green gunk at the battery contacts, you might as well pop it open to clean what you can't see now. I've had good luck with vinegar & a brush, then a wash with alcohol, then a three day drying off before i power it up.

[kusmi]

(03-26-2015 03:30 PM)Den Belillo (Martinez Ca.) Wrote:  I've had good luck with vinegar & a brush, then a wash with alcohol, then a three day drying off before i power it up.

You say you even used vinegar on the circuit board? If so, i will try that too (if I see green stuff on it, once opened)

[Dave Frederickson]

(03-26-2015 11:02 AM)kusmi Wrote:  2.) what is your recommended method to remove copper hydroxide? Just brush it off or are there some recommended chemicals?

DeoxIT has a formulation specifically for battery contacts. It works on the calculator contacts, too.

[PANAMATIK]

(03-26-2015 11:02 AM)kusmi Wrote:  [*]Whenever a digit is shown, the top-most and top-right segment is always "ON", so all 1s appear as 7s, etc (see attached images, the first shows the display when I enter 1111111111, the second shows the number -1234567890). Those additional two segments are only ON when the actual digit is displayed - if the digit is OFF, all segments are OFF.

A very common defect of a 30s calculator is one or two missing segments in all digits, because the contact of this segment is lost. This is very easy corrected by what you have done, twisting and reestablish the contact somehow.

But it is more unusual, that segments are lit always. The reason could be a short between some segments, but unfortunately it points more to a defective display driver. But I hope I am wrong because I don't want to disappoint you.

IMO the 30s are very resistant to real damage. I repaired some of the 30s just by opening the case, do some cleaning and putting it together again. You should try it. The only difficult part is to open the case, which needs some real force.

http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=151125

Bernhard

[Jeff_Kearns]

(03-26-2015 05:27 PM)PANAMATIK Wrote:  The only difficult part is to open the case, which needs some real force.

I have had great success with this illustrated technique.

Jeff