OT? Apple Stylewriter problems (update) - test-drb@ccmp.vtda.org

21 Jan 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