OT? Apple Stylewriter problems (update)

From: Mark Tapley <mtapley_at_swri.edu>
Date: Mon Jan 21 10:45:47 2002

Toth asked:

>Are there 3 indentations around the edges of the fasteners? If so, these
>could be a type of Japanese fastener often found in mid '80s to early '90s
>video game systems. Bits that fit those kinds of fasteners are available,
>at about $1.50-$2 each, and they come in 2 different sizes.

Hmmm - will look again. I was specifically looking for anything I could get
purchase on to turn the things, though, and did not see it.

Tony said:

>Hnag on... I thought it was one printhead heater that was out. In which
>case it's likely that 8 of the 9 transistors are still fine.

Right ... but I don't know which one. I was hoping to end up unsoldering
them all, and finding the bad one by the first-order test, then putting all
but that one back and ordering a single replacement. In which case I might
as well start off with just the four I couldn't get my VOM onto during the
in-use testing I tried. I did not count on destroying components as I
pulled them, however. Glad I only tried 4.

..."heater?" IIRC, Pete said these transistors work up to 100 MHz and they
are being used to drive *heaters?* Does that mean the other 17 or so
connections to the print head carry the which-pixel information and
whatever (piezoelectric?) pulse it takes to actually send out the squirt of
ink? Oy. Or are there 8 heaters and one for the jet pulse, and the thin 17
carry the jet-selection info? Maybe I am going to be be interested enough
to trace this whole circuit out. Or maybe I should just shred one of the
print heads to see what's inside it.

>Do you know
>if you tested one that was related to the dead row of pixels?

No. I *thought* so, from the in-operation tests and locations on the
ribbon-cable connector, but since I still have not got the PS working, I
can't confirm that by trying to print again with the 4 transistors removed
- which is the only way I'd believe at this point.

BTW, would *that* toast anything?

>It won't be. A diode junction is not an ohmic conductor, and there's no
>reason why it should show the same 'resistance' under different test
>conditions (such as changing the range on the VOM).

Figured, which is why I put quotation marks around "resistance".

>In the end it'll be to a +ve supply line, but there might be other
>transistors or current sensing circuitry in the way. However, since this
>is common to all pixels, it's not a problem (yet).

'cause I haven't tried to test or disassemble it (yet) >:-)

>Probably resistors (read the numbers like you would the numbers on a
>capacitor -- so 151 -> 15*10^1 = 150 Ohms, and so on). I'd expect a
>resistor from base to emitter and another resistor from base to some kind
>of open-collector output (maybe a discrete transistor, maybe a chip).

I'll check, but that's consistent with what I've seen so far, I think.

>The fault, of course, might be further back in the circuitry, so you
>might have to trace out this array of components.

More havoc to wreak...

>Any depressions in those heads at all? Any way a tool could engage with them?

I don't think so. I'll have one more look before I try the soldering iron
(didn't get to it this weekend).

>Oh, it can't be that complicated. After all, there are likely to be 9
>identical stages. I would conentrate on the base of the power
>transistors. What connects there, what does it connect to.

I don't see 9 identical groups of components anywhere else. There are
several large DIP packages, one of which I'll bet I run into on the far
side of the surface-mount things.

>This 'surface mount array' : What does it contain? Any more transistors?
>Any open-collector driver chips nearby?

The only things I saw were the little (?) resistors described earlier. I
didn't look at the chips nearby - I'll try that next chance I get.

>Unlikely. The voltage is not going to damage parts of this printer, or
>any other classic computer you're likely to be working on.

OK, that's reassuring.


And I have an offer of a replacement wall-wart and PCB coming from a very
kind list member. Not an exact match PCB, which could lead to more fun
still, but we'll see.
                                                        - Mark
Received on Mon Jan 21 2002 - 10:45:47 GMT

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