Troubleshooting an IBM 5155 - (portable personal computer)

[Tony Duell]

> 
> > 
> > 
> > The heads are selected by U4 (75451 dual AND gate/driver), 
> > the outputs of 
> > which are pulled to+5V, and slo drive the bases of Q7 (Head 1) and Q6 
> > (Head 0), PN2222 transistors via restors. One input of each 
> > of the AND 
> > gates comes from the power-OK circuit, built round Q9 and Q10 
> > (as this is 
> > common to both heads, it's working correctly), the other 
> > input comes from 
> > the sides select signal on the connector (U4b, for head 1) or 
> > from that 
> > signal inverted by U8b (7414) on U4a, for head 0. That should 
> > give you 
> > some components to check.
> > 
> Are you sure U4a drives Q6 and U4b drives Q7? Tracing the board shows them
> on Q7 and Q8. Yikes. Any chance you could scan the schematic and email it?

No, I misread it. It's Q7 and Q8 as you said. Q6 is the erase driver.

> 1bpp tiff, bmp or pcx would do. The higher the resoultion the better, but I
> could probably make due at 150dpi.

Alas I have no scanner, and nothing to connect it to :-(

-tony