|Re: Another thought.|
Message #5 Posted by Tony Duell on 21 May 2007, 1:27 p.m.,
in response to message #4 by PeterP
1) I measured the current the unit is drawing on power-up and selftest and it is a bit less than 1A (BTW - this caused me to buy
Well that's interesting. The picofuse in the HP battery is rated at 2A (early battery packs) and 5A (later ones). So something is causing this unit to draw too much supply current only under specific circumstances.
I assume you were measuring the current while the drive was spinning and/or the head moving during the self-test. That's when the unit draws the highest current
I must admit I tend to go totally OTT when it comes to tools and test gear.
a better DMM. Fluke was a bit out of my range but I went for a Sperry DM-4400A and it immediately improved my handling of measurements and the like. And it has an amp-meter which my prior 5.95 USD pocket DMM did not have) So that is okay, if a bit low according to your expectations
3) Then I also found the TP with the help of your schemata and the PCB (which is nicely labeled I must say). I can only try to imagine how much painstaking work it must have been to draw those schematics!
Actually, the 9114 schematics didn't take that long. The HP9100B was a lot worse. I'll explain. In the 9114, you have a number of 'large chips' that have well-defined functions. There's a 68x09 processor. It can only be used in one way. It needs a clock input, it needs reset, it has address, data, and control buses that go to the other chips on the board, and so on. The only 'inventive' part is the PSU. OK, there were a couple of little bits of logic to sort out, but most of it could realistically have only been wired one way, and was wired that way.
Now think of a board of simple logic chips -- say a board from a 9810. You come across a 7400. It's a quad 2 input NAND gate. Now those NAND gates could be used in many ways, they needn't all be used in the same part of the circuit. Maybe 2 are cross-coupled to make an SR flip-flop. Maybe one is cross-coupled with a NAND gate in another chip to make an SR flip-flop. Get the idea. A lot more to work out.
And now think of the 9100. No chips at all in the logic section. Just boards of transistors and a big board of mostly diodes. Now a transistor could be almost anything -- part of a flip-flop, part of a buffer circuit, even part of a power supply. You've got to do a lot of work to have some idea of the overall stuff on the board.
a) In the post which described the home-made PSU with a charger from Radio-Shack, it was mentioned to run the charger at 6.5V. I did the measurements below at both 6V setting and at 6.5V setting. The values in brackets relate to the test with the 6.5V setting.
a) I tested VC on TP8, which was at 4.97V (4.97V)
b) I tested +5V on TP 10 which was 5.02V (5.02V)
c) ! I tested 12V on TP9. And this one only showed 5.76V (6.22V) !
So there seems to be clearly something wrong here!
The 12V supply is only turned on when needed -- that is when the disk drive is in operation (the 12V line is used for the motors). When it's turned off, TP9 will show the battery voltages less a little bit. Connect the meter to TP9 again and see if the voltage goes up to 12V when it's using the disk (e.g. during the self test or a CAT operation).
d) I also did the test you suggested with 1) writing something on the disk with the 9114, then 2) run a test, startup, initialize etc with the 9114a and 3) try to read the disk in the 9114B again. This test worked. cat :1 showed the very same files I had copied onto it.
So, it seems that something with the 12V circuit is broken. Is
Given that the thing can read a disk, I think not. The motors must be turning.
More likely it's a problem with the write circuit or the head selection circuit. This is on the PCB attached to the drive itself, and is mostly discrete SMD components. Actually, I've had a 9114A in for repair where a couple of those transistors had failed. I replaced them with pretty generic types and had no problems.
One thing that might not be obvious. On my schematics, a transistor with a circuit round it is just that -- a transistor. One with a square box round it is a 'digital transistor' -- it includes base resistors, etc.
there any chance that we can figure out what without the scope/logic probe? It so happens that I was able to find a HP-IL
Maybe, but it's a lot easier with the test gear.
1631D Logic Analyzer and Digital Scope for rather cheap (I believe), yet i have not used a Scope in ages and never was very good at it at all. This was just the last standard HP-IL device I did not have yet and it was a good bargain.
Ooooh very nice. I hate to say this, but the way to get good at using test gear is to use it -- to practice. And this is a fairly good thing to practice on.