On 05/01/2016 03:43 PM, Gareth Magennis wrote:
"bitrex" wrote in message ...
On 05/01/2016 03:20 PM, Gareth Magennis wrote:
"bitrex" wrote in message ...
On 05/01/2016 02:37 PM, wrote:
On Sunday, May 1, 2016 at 12:49:54 PM UTC-4, bitrex wrote:
On 05/01/2016 12:26 PM, wrote:
From your description, it is mechanical. Is there a way, using a
dental tool or similar that you might test each wire in the loom as
it goes into the connector? I expect you will find the problem there.
Peter Wieck
Melrose Park, PA
?
Press down on each separate wire as it goes into the MPC. A spade-type
dental tool is excellent for this purpose. The point being that if the
connector holds when under stress, but fails when there is no stress,
it is very most likely mechanical.
And, of course, it could be two-or-more things if you, in fact,
bridged something replacing a resistor.
Peter Wieck
Melrose Park, PA
Cool! The dental-spade trick seems to have found a candidate (I used a
tiny tiny phillips head screwdriver for manipulating each wire on the
header individually.)
Purple wire. When I wiggle that one around the keypad becomes
responsive. The others have no effect.
I did some reading and I think the reason the keyboard and the sound
engine is behaving goofy is because I swapped the RAM backup battery,
and it's become corrupted. The processor has no internal memory, and
uses the external battery-backed RAM for both its heap/stack and storing
patch data.
There's a startup key combination that instructs the processor to wipe
the memory and re-initialize, but of course I can't execute it when the
membrane buttons aren't working...: )
Here's what I put in my Service Report on an Alpha Juno 2 I repaired
January this year:
"Check Battery. Reinitialise RAM. Replace Power Supply capacitor.
Resolder all joints on Power Supply PCB. Clean all key contacts and
contact PCB"
The system here was corrupted, though the battery was good. You need to
do the reinitialise procedure.
And have a good look at the Power supply too.
Gareth.
Thanks! All power supply filter caps have been replaced with fresh
Nichicons; one of them looked like it was starting to get the plague.
All the voltages are within tolerances and the HV inverter is putting
out around ~90 VAC.
All the keys were removed and the membrane contacts were cleaned. That
was a pain in the ass job.
OK, so it looks like these are the common ailments of the Alpha Juno 2!
Gareth.
Apparently both the EL backlight and the inverter are prone to failure.
The inverter looks like a pretty simple blocking oscillator
configuration, either the filter cap or transistor can fail. If the
transformer fails then you're probably SOL.
The EL material fades out over time.
The inverter on mine was putting out good HV as is, but the EL material
had faded. I happened to have some EL material lying around so I fitted
that, but in the process the old LCD display basically crumbled as I
removed it. Fortunately I found an unlit display module that was pretty
much an exact replacement on eBay - 3 for $3. I just had to scrape off
the reflective backing. The contrast resistor needed adjustment though.
Some people disconnect the inverter and just replace it with a standard
16x1 LED display, fed from the +5 rail, that mod is apparently drop-in.
A few people have replaced their AJ screens with OLED displays, but they
aren't 100% compatible and need a hacked firmware ROM to support them.