Membrane keypads again.

[bitrex]

Haven't had time to work on this project recently due to illness.
I'm back at it.

I'm still trying to figure out the reason that this synthesizer's
membrane buttons keep being non-responsive. Again, there's a
certain multi-wire header that plugs into the main board where if
I tug on it, things function normally. If I let it go slack, the
buttons become non-responsive again. I've cleaned all the
connections, reflowed the solder joints to the headers but still
no luck.

Can anyone suggest a methodical way to isolate where the problem is?

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[bitrex]

bitrex <bit...@de.lete.earthlink.net> Wrote in message:

Connector in question is 67-74 on the mainboard schematic in the
following service manual:


http://www.synfo.nl/servicemanuals/Roland/JUNO-2_SERVICE_NOTES.pdf

[pf...@aol.com]

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

[bitrex]

Sure. How would the test procedure go precisely?

[bitrex]

On 05/01/2016 11:14 AM, bitrex wrote:
>
> Haven't had time to work on this project recently due to illness.
> I'm back at it.
>
> I'm still trying to figure out the reason that this synthesizer's
> membrane buttons keep being non-responsive. Again, there's a
> certain multi-wire header that plugs into the main board where if
> I tug on it, things function normally. If I let it go slack, the
> buttons become non-responsive again. I've cleaned all the
> connections, reflowed the solder joints to the headers but still
> no luck.
>
> Can anyone suggest a methodical way to isolate where the problem is?
>

I have a suspicion this might not be a mechanical issue. The connector
I'm actually yanking on is 34-52, on page 18 of the service manual,
labeled "Cartridge Board."

I swapped out a resistor that's connected to ground from the LCD display
to increase the contrast, changed from 5.6k to 1k. That resistor is
right next to IC20, which is connected to the "Cartridge Board"
read/write lines.

I wonder if that bollocked something up, because the synth didn't have
this issue prior to the LCD swap.

I don't see any obvious solder bridges but I'll look again...

[Jeff Liebermann]

On Sun, 1 May 2016 11:14:50 -0400 (EDT), bitrex
<bit...@de.lete.earthlink.net> wrote:

>Can anyone suggest a methodical way to isolate where the problem is?

Find which wire on the connector is not making a connection. Power
off. Attach wire hooks or tack solder some wires to opposite sides of
the connector. Attach an ohmmeter. Now, wiggle things around until
you determine where things are intermittent.

A close photo of the connector area would be helpful if you want me to
make a guess(tm).

I couldn't find 67 - 74 on the main board schematic (Pg 18). That are
the row and column coordinates or maybe a large nearby component?





--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[bitrex]

On 05/01/2016 01:45 PM, Jeff Liebermann wrote:
> On Sun, 1 May 2016 11:14:50 -0400 (EDT), bitrex
> <bit...@de.lete.earthlink.net> wrote:
>
>> Can anyone suggest a methodical way to isolate where the problem is?
>
> Find which wire on the connector is not making a connection. Power
> off. Attach wire hooks or tack solder some wires to opposite sides of
> the connector. Attach an ohmmeter. Now, wiggle things around until
> you determine where things are intermittent.
>
> A close photo of the connector area would be helpful if you want me to
> make a guess(tm).
>
> I couldn't find 67 - 74 on the main board schematic (Pg 18). That are
> the row and column coordinates or maybe a large nearby component?
>

I think the problem may not be mechanical, as I've noticed that now the
keyboard is having issues triggering as well, which is not connected to
the same area.

I think I screwed something up swapping R66 on page 18 near the LCD, and
the processor is having trouble with read/writes or something.

[Jeff Liebermann]

On Sun, 1 May 2016 13:47:13 -0400, bitrex
<bit...@de.lete.earthlink.net> wrote:

>I think the problem may not be mechanical, as I've noticed that now the
>keyboard is having issues triggering as well, which is not connected to
>the same area.

Well, it wouldn't hurt to eliminate the keyboard as a possibility. Put
an ohmmeter across a row and column on the keyboard and measure the
contact resistance with an ohmmeter. Try all the button combinations.
If the resistance seems resonable, move on to looking for another
culprit.

>I think I screwed something up swapping R66 on page 18 near the LCD, and
>the processor is having trouble with read/writes or something.

5.6K goes to Vo on the LCD display, whatever that does. If it's
carbon comp, check the resistance with an ohmmeter. They change over
time and absorb moisture. However R66 doesn't seem to go anywhere
except the display making changes to keyboard and buttons rather
unlikely. Dunno.

[bitrex]

On 05/01/2016 01:58 PM, Jeff Liebermann wrote:
> On Sun, 1 May 2016 13:47:13 -0400, bitrex
> <bit...@de.lete.earthlink.net> wrote:
>
>> I think the problem may not be mechanical, as I've noticed that now the
>> keyboard is having issues triggering as well, which is not connected to
>> the same area.
>
> Well, it wouldn't hurt to eliminate the keyboard as a possibility. Put
> an ohmmeter across a row and column on the keyboard and measure the
> contact resistance with an ohmmeter. Try all the button combinations.
> If the resistance seems resonable, move on to looking for another
> culprit.
>
>> I think I screwed something up swapping R66 on page 18 near the LCD, and
>> the processor is having trouble with read/writes or something.
>
> 5.6K goes to Vo on the LCD display, whatever that does. If it's
> carbon comp, check the resistance with an ohmmeter. They change over
> time and absorb moisture. However R66 doesn't seem to go anywhere
> except the display making changes to keyboard and buttons rather
> unlikely. Dunno.

R66 controls the contrast of the LCD. I had to swap it out as the new
LCD display didn't seem to be 100% compatible, and it was invisible with
the stock 5.6k resistor. 1k makes it legible again.

R66 is sitting about half a millimeter away from the deglitching cap for
IC20. I'm looking to see if I might have bridged it somehow.

[pf...@aol.com]

On Sunday, May 1, 2016 at 12:49:54 PM UTC-4, bitrex wrote:
> On 05/01/2016 12:26 PM, pf...@aol.com 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.

[Gareth Magennis]

"bitrex" wrote in message news:tarVy.6021$IU7....@fx19.iad...

Hang on, this is the first we have heard of an LCD swap.

Did you get the new LCD from Roland, and/or is it a part that it known to
work properly in this keyboard?

I smell a Red Herring.



Gareth.

[bitrex]

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...: )

[Gareth Magennis]

"Jeff Liebermann" wrote in message
news:mhgcibpgtjil6napg...@4ax.com...

On Sun, 1 May 2016 13:47:13 -0400, bitrex
<bit...@de.lete.earthlink.net> wrote:

>I think the problem may not be mechanical, as I've noticed that now the
>keyboard is having issues triggering as well, which is not connected to
>the same area.

Well, it wouldn't hurt to eliminate the keyboard as a possibility. Put
an ohmmeter across a row and column on the keyboard and measure the
contact resistance with an ohmmeter. Try all the button combinations.
If the resistance seems resonable, move on to looking for another
culprit.

>I think I screwed something up swapping R66 on page 18 near the LCD, and
>the processor is having trouble with read/writes or something.

5.6K goes to Vo on the LCD display, whatever that does. If it's
carbon comp, check the resistance with an ohmmeter. They change over
time and absorb moisture. However R66 doesn't seem to go anywhere
except the display making changes to keyboard and buttons rather
unlikely. Dunno.

R66 is most likely contrast or viewing angle adjustment.
It might be a good idea to check all the pullup resistors (RA3) are all
present and correct.

It is probably another good idea to just resolder everything around that
part of the circuitry, including the Gate Array, just to eliminate dry
joints as the problem.
That's a 5 minute job at most.

And, if you (the OP) have replaced R66, go look at it again with a loupe or
magnifying glass and check you haven't inadvertently shorted something out,
or there is maybe some solder debris sitting on the Gate Array pins.



Gareth.



Gareth.

[Gareth Magennis]

"bitrex" wrote in message news:QlsVy.14079$tt5....@fx34.iad...

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.

[bitrex]

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.

[Gareth Magennis]

"bitrex" wrote in message news:WOsVy.43993$1Q2....@fx33.iad...

OK, so it looks like these are the common ailments of the Alpha Juno 2!

Gareth.

[bitrex]

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.

[Gareth Magennis]

"bitrex" wrote in message news:7etVy.15605$u52....@fx13.iad...

Yes, I recently replaced the LCD on a Juno G, which was no longer available.
I got the updated LCD from Roland, complete with firmware upgrade, that
would enable the Juno to properly talk to the new LCD.




Gareth.

[Gareth Magennis]

Yes, I recently replaced the LCD on a Juno G, which was no longer available.
I got the updated LCD from Roland, complete with firmware upgrade, that
would enable the Juno to properly talk to the new LCD.

Oh, and after supplying the serial number of this Juno G, Roland supplied
the new LCD and firmware update for free.

The customer was delighted, as was I, even though I made no profit on the
parts.

It was an uneconomical to repair, otherwise.




Gareth.

[bitrex]

On 05/01/2016 02:37 PM, pf...@aol.com wrote:

Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

[pf...@aol.com]

On Monday, May 2, 2016 at 6:49:30 AM UTC-4, bitrex wrote:

>
> Question is now that I've located the problem, what's the most effective
> way to make an expedient repair? I can't seem to get the wire to make
> firm contact no matter how I poke at it, and it seems impossible to pull
> out of the header.
>
> I'm thinking about just clipping it off, heat shrinking a longer section
> to it and then soldering it directly to the underside of the board, but
> that seems a bit barbaric.

The solution that I use for this issue, typically, is to strip a small piece of fine gauge (appropriate to the MPC) copper wire -leave it on the spool for leverage - preferably hardened, and I keep a couple of small spools _only_ for this purpose, and push it down the connector beside the broken wire. Touch this wire with a hot iron and a bit of solder to bridge the break, and then cut it off with fine nippers. If the MPC is very fine, I will pre-tin the wire as it may not flow down the hole. If and then, a bit of hot-melt or similar to insulate any exposed wire. Done.

I have been known to use a silver-plated sewing needle, broken off to the proper length if copper would be too soft. They solder very nicely.

[bitrex]

Excellent, will try. Thanks!

[bitrex]

On 05/02/2016 07:01 AM, pf...@aol.com wrote:

OK, so the mystery deepens a little bit. I was having trouble getting
the shimming to work consistently, so I tried jumpering directly from
the control wire to the underside of the PCB.

Turns out that there's still a problem, even with the wire jumpered
directly to the board. But when I pinch the wire junction in my
fingertips, everything works normally.

Pull-up resistor gone open on that line, maybe?

[bitrex]

Yup, that was it. Pullup resistor on that pin has gone bad!

[Gareth Magennis]

"bitrex" wrote in message news:b2NVy.66828$Bn7....@fx26.iad...

I said that quite some time ago.

R66 is most likely contrast or viewing angle adjustment.
It might be a good idea to check all the pullup resistors (RA3) are all
present and correct.

Gareth.