tmaster@ucscb.UCSC.EDU (The Master) (02/01/90)
In article <15800046@ux1.cso.uiuc.edu> cs225af@ux1.cso.uiuc.edu writes: > >The chip is the MC3470P chip. It has basically exploded, and I'm VERY >scared to plug it back in (when it blew, my MONITOR dimmed.... I'm not >about to plug this piece of junk back in until I am quite sure it's OK >for reasons fairly obvious!) > >Oh, where, oh where can I get this chip? > > >-- rubio JDR Microdevices carries them ($1.95). phone is 800-538-5000. Only problem is that their mininum order is $10, and it is $3.50 for shipping (still much less than the apple dealer. Buy a few extra, get some blank disks, whatever..) Ideally, if there is a good electronics place in your area, try them first. Living in (near) silicon valley spoils one for ease of getting replacement parts and so forth. I'm not affiliated with JDR Microdevices, but have found their service (retail store) very good. Prices are generally rather close to prices of other places also. The Master tmaster@ucscb.UCSC.EDU
cs225af@ux1.cso.uiuc.edu (02/02/90)
A couple more questions regarding my blown Disk II!!
First of all: thanks to the many people who have sent information and help
in posts and via email. I have enough info that I should be
able to replace the chip that blew. Your assistance is
greatly appreciated, and I'm glad that there are still great
Apple II owners out there ready to lend a helping hand....
Hopefully, if I get a new chip to replace the one that blew, the old crate
should be up and running. However, many people (including the infamous
Apple service center personnel) have told me there is a good chance that the
chip that blew took other electronics out with it.
Seeing as how the place I will probably end up ordering the chip through has
a minimum order of $10 or $20, if I can find out what other chips, etc. might
have gone bad I would like to order them at the same time, just in case, to
push my order up to the minimum (even if everything works, spares are nice
to have around!)
I know that the old DOS 3.3 manual had schematics of these Disk IIs and their
analog card. I, of course, don't have this manual.
Rather than send me the schematics (I couldn't make much sense of them
even if I had them!), perhaps you or someone you know could answer a couple
of questions about the Disk II Analog Card:
first off, in case there are other models of this card (yeah, right, but
just in case :-) here's what it says in the lower left corner of the board:
apple computer inc. (C) 1978
DISK II ANALOG CARD
600-0038-____
Are we talking about the same board? Good. Here's what I would like to know:
* The chip that blew is the MC3470P (someone told me this was a Floppy Disk
Read Amplifier). It is on the left side of the board, about half-way up,
near the R20 and C12 markings on the board (it's socketed). Can anyone
tell/guess from personal knowledge or from the schematic what other stuff
this chip might kill if it blows up?
* There is a potentiometer on the board just above the 'inc.' of the
'apple computer inc.' label on the card. It is marked R28 on the board.
It is labeled as "Helit rim Model 91". Any guesses about what this thing
does? I accidentally turned it and until I turned it back near where it
used to be it wouldn't read or write to disks successfully. Hopefully it
is about where it should be again, as the drive was reading and writing OK
until just before the chip blew. If it isn't, can anyone tell me what it
could harm, if anything?
* In the few days before the chip went up in a puff of smoke (more like a long
steady stream, actually :-) I'd been running the drive a whole lot,
verifying my 5.25" stuff. About an hour or two before ->|BAM|<- the drive
stopped reading or writing to the BACK sides of my disks (the FRONTS worked
just fine!) I suspected it was the pressure pad (that little cottony thing
that presses the disk surface against the read-write head). After I fluffed
the pad up a bit and put it back in, the drive did in fact verify one of my
disks, front and back sides. Just after it finished side 2, *pop*
Was it most likely the pressure pad? Or could the problems w/verifies have
had something to do with the impending chip failure?
* Assuming they don't cost too much (indications from other people lead me
to believe each chip costs next to nothing), I already plan to buy
replacements for all four socketed chips on the Analog Card (can't hurt,
can it?) including the apparently very failure-prone 74LS125N. Is there
anything else I should look out for? Anything else I should get?
Anything I SHOULDN'T get?
Thanks for your patience, and once again, thanks for all your help.
-- rubiostephens@csadfa.cs.adfa.oz.au (Philip Stephens) (02/02/90)
In article <15800048@ux1.cso.uiuc.edu>, cs225af@ux1.cso.uiuc.edu writes: > > * There is a potentiometer on the board just above the 'inc.' of the > 'apple computer inc.' label on the card. It is marked R28 on the board. > It is labeled as "Helit rim Model 91". Any guesses about what this thing > does? I accidentally turned it and until I turned it back near where it > used to be it wouldn't read or write to disks successfully. Hopefully it > is about where it should be again, as the drive was reading and writing OK > until just before the chip blew. If it isn't, can anyone tell me what it > could harm, if anything? This potentiometer simply controls the number of revolutions per minute the drive runs at. It cannot harm anything except for diskettes that you write to when it is running at the wrong speed! Someone else can answer the remaining questions! _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_ Philip J. Stephens -_- `My Apple II+ may only have 64K, one _-_ _-_ Department of Computer Science -_- 5 1/4 " drive, a stuffed joystick, _-_ _-_ University College, Canberra -_- and run at 1 MHz; but it's mine!!!' _-_
mrn31796@uxa.cso.uiuc.edu (02/03/90)
JBL microdevices sell the adapter. Look for them in the computer shopper. -Mike Neuliep E-mail: mrn31796@uxa.cso.uiuc.edu [tag under construction]