HP-42S - Is this internals picture normal?

[weenis]

This forum has been a great help in researching 42s calcs and such, i've been a long time reader but finally had the need to post.

I have a Rev. A HP-42S that I purchased on that one auction site. It had an issue beeping when turned on or, and when the calculator was used. I needed a case also, so I thought if I can repair the 42s, I have 2, if I can't repair it, I have a case for my transplant. It turns out one of the connections on the memory chip was loose, so I was able to solder it and the beeping went away. All self tests pass.

Now here's my question, when I was looking at the internals, it looks different than some of the pictures of other 42s calcs, like mine is missing capacitors

Here's a picture-



Are there supposed to be capacitors within the red boxes?

[Diego Diaz]

Hi Weenis, and welcome!

The 42s board in the picture is perfectly normal.

The upper unused pads, seems to be intended for yet another capacitor but I've never found it populated.

The other empty smaller pads are for a glass encapsulated Schottky diode which is an alternative to the TSOP plastic diode that you can see in your board. Seems that HP decided to keep both posibilities available and I've found boards with glass diode or TSOP indistinctly.

Hope this helps.

Diego.

BTW, Since you've had to open your 42s why not take the chance and replace the original 8K RAM chip with a new 32K one?

[weenis]

Thanks for your reply.

I may do the memory upgrade. I'm going to just play with the calculator for now though.

I think my next project is a WP34S.