HP-97 Circuit

[AndiGer]

Hi Tony,

Re-checked with old and new layout of the PCB - yes, you are right. Must have been dreaming when I meant I found that :-).

But there are other mistakes in the Service Manual.

In figure 4-9 U7 to U9 are marked as ROM3 thru ROM5 whereas due to table 4-6 there is no ROM4. U9 due to its position in figure 4-9 should be 1818-0233 i.e. ROM3. It is wired totally different compare to the other four ROMs.
Pin connections of U5 to U8 are all the same and connected to the corresponding pin between each other as seen in figure 4-10. So the position of these chips doesn't matter (if pin orientation is ok).
In figure 4-10 U7 is marked ROM5, U8 ROM6.

So we get a mix-up of table 4-6, figure 4-9 and figure 4-10.

In a real calculator I found 1818-0230 at position of U7 of figure 4-9, 1818-0229 at position of U8.
Due to the mix-up I can't tell neither 1818-0230 is ROM5 or ROM6 nor for 1818-0229.

Andi