HP 46 repair

[vassilisprevelakis]

(05-03-2019 08:54 AM)AndiGer Wrote:  But to get it back to the right orientation together with the print drum and the solenoid sensors will be complicated. Just now don't dare ...

Hi Andi,

I fully agree with you. That printer totally intimidates me. I've looked and looked for assembly-disassembly drawings on the net and did not find any, so when my HP-46 developed a printing problem I knew that if it was the printer itself I'd be in deep trouble.

The problem is that the last two columns print intermittently (rightmost hammers 17 and 18 have a problem).

I looked at the printer connector and was very happy to discover that the printer is not receiving a signal to fire these hammers, so the problem is with the motherboard electronics.

My next suspect were the transistors that drive the hammers, but these turned out to be OK.

So the most likely suspect is the U8 CMOS quad two input NOR gate IC (4001). Of the 4 gates two are used to drive the transistors for hammers 17 and 18. The other two are linked together as two inverters in series driving the 4th display line. (I am not sure why, as the other 3 lines are sent directly.

So now I am waiting for some 4001s so that I can go ahead with the repair.

Cheers

**vp

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