Deaf Alesis HD24
On Dec 24, 8:17*pm, "Richard Crowley" wrote:
As I was setting up to record a ~100 voice choir and ~50 piece
orchestra last weekend, I discovered that my HD24 (which I had
converted to XR a few years ago) was deaf as a post. Everything
else appeared to work just fine, but no analog input or output.
(I don't have any way to test digital in/out).
I unplugged everything and removed it from the case and opened
it up (with my trusty Leatherman tool which hangs from my belt).
The daughter-board that plugs onto the interior ends of the analog
input and output boards was "hanging by a thread". Of course, there
is no mechanical support for this board. It hangs off the lever-arm
ends opposite from the input connectors (which are all that hold
the analog boards). Now I know why people recommend more gentle
transport practices and methods. :-(
Alas, after re-connecting the daughter board, the HD24 no longer
even recognizes the XR upgrade. In fact it acts exactly the same
as if the whole analog section weren't even connected (I tried it).
The daughter board powers the analog boards, and the power supply
cable to the daughter board appeared to have the voltages that we
would expect (although I don't know that it is actually documented
publicly?)
I re-seated all the ribbon and power connectors. I triple-checked
to see that the daughter board was properly lined up with the input
and output boards (as cautioned in the XR upgrade instructions)
Someone brought a Zoom R16 which records 8 channels to an SD
flash memory card. It worked OK, but the metering is really primitive
and it was difficult to set decent levels.
Dunno what I'm going to do about my HD24. I guess I will try putting
the old (non-XR) boards back in to see if I can make a differential
diagnosis of the problem location.
The first thing I would do is to check the analogue power supplies,
which should be something around +15v and -15v. (possibly as high as
+- 18v) If one or both voltages are not present in the analogue
section, the machine may well behave as though there is no analogue
circuitry present, while the computing section, running on 5volts,
will be unaffected and even unaware the analogue section is not
working.
If the analogue section uses 8 pin DIL op-amps, this is the easiest
place to check - select a convenient chip and carefully meter each of
the 8 pins in turn, with the negative meter probe on a ground point.
Make sure you don't short 2 pins together with the probe, or you could
kill the chip.
Gareth.
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