HP 10 printer issue

[tangdfx]

Hi, All

Recently I acquired a good cosmetically HP 10.

[attachment=10462]


It can print but there is an issue when print digit zero and also the decimal point will be double print.

You can see from the picture the "0" is enlarged but meanwhile other digit is normal.

I already search the forum and I find another case is similar with mine.

Here is the link: https://archived.hpcalc.org/museumforum/...ight=HP-10

I already try a lot of approaches such as I change the 1826-0287 with a new LM339 comparator.

I also change the the old transistor with BC338.

Now I don't know where to go.

I am suspect the printhead timing circuit has something wrong.

[attachment=10463]

Otherwise maybe the CPU has defected which integrate the PIK in one die.

[attachment=10464]