MS8 Midi switcher Glitching problem, Need help from the wise man

[jstbrowsin]

Hi there,
I have owned this MS8 Midi switcher for about 2 years now and never had any faults, but recently when I power up the rack the LCD display on the MS8 shows no characters and just seems to freeze. However if I power it down and then back up again using the switch at the back of the unit it seems to come right, but not always sometimes it takes a few flicks of the switch to get it to come right, then I notice that some of the preset titles on the display have changed to nonsensical characters.
Don't get me wrong here sometimes it just powers up fine but mostly it doesn't and its embarrassing when the rest of the band is waiting for me to sort it out
I have included the schematics for the boards in hopes that some wise persons (ENZO maybe) here can help me identify the problem and fix it myself. I am good at following instructions ( I have modified successfully with help from ENZO and others my TS60 amp and built a few pedals etc) but still haven't quite inherited the knowledge and skills to find the problem myself. . .yet. But I am working on it. . .

I hope someone here can help me here please. . .

TIA
Trevor

[Enzo]

On the main schematic, lower left area, see the battery B1? It is a CR2032.

CR2032 is a very common coin cell. They can be had with little sodler pins sticking down and they would be soldered onto the board, Or they can be clicked into little coin cell sockets, and easily changed. Either way, this thing is about the size of a quarter. Check the voltage on top of it, the + side, with respect to ground. If it is less than 2.5v, change it. 3V or even a little more is fresh battery.

Plaun coin cells can be bought at Radio Shack. The solder tab ones have to come from some place like Digikey.


I just bet your battery is low.


Other than that, any IC in a socket, rap on the top of it sharply with your knuckle.

[jstbrowsin]

Hi Enzo we meet again. . .
Thanks for your quick response and sorry I forgot to mention that I checked the battery and it measures fine 3.3V if I remember right.
So by rapping on the top of the IC's with my knuckle is this the same as the "chopstick method" for checking amps? What am I supposed to be hearing from the IC? or seeing on LCD maybe?
Can you elaborate a bit more please?

TIA,
Trevor

[Enzo]

ANy IC in a socket has the potential to lose good contact in the socket pins. SO by rapping on the top of each, it kinda settles the IC into the socket adn is usually sufficient to refresh the pin contact surface. In the old days I might have suggested pop each IC halfway out of its socket aqnd push it back in, but over time I found that just shoving each chip a little is enough.

That may do nothing, but it takes 10 seconds to go down the board popping on them.

But while the battery may be fine, sounds like it is, look at the battery circuit in the drawing. See how the battery voltage adn the power suopply voltage are mixed by a couple diodes and ultimately it feeds the power pin on a RAM. With power off, is the battery voltage actually getting there?

And make sure the logic power supply is up to voltage and clean.

Beyond that, hard to say.

[jstbrowsin]

Thanks again Enzo I'm gotta head back to tech now (mock exams for our big external exam on saturday) but I'll endeavour to make these tests today and I'll report back

Cheers
Trevor

[jstbrowsin]

Hey Enzo,
Sorry I haven't been in touch, my little girls gone away to the deep south to live with her mum (err NZ South Island that is) so I wanted to spend as much time with her before she left.

I found the culprits to my problem. Firstly I was getting back EMF (I think that's what its called ) from reverse polarity in my A-B relay system I have in my rack to switch in and out a preamp I use in the loop of my amp. Fixed that but it was still doing the same thing so I tried knocking the chips and sure enough one of the chips was loose in the MS8 err that will do it eh
so all's well now thanks again for all your help my friend.