[SOLVED] Ambika strange behaviour (freezes, strange LCD characters, reloading)

My two freshly built Ambikas has identical strange behaviour.
So, briefly, if I turn the Ambika on without midi in cable, it works as it should. But if I begin to send MIDI notes (not very often), all voices are working fine, but there are some flashing strange symbols on display above the 3rd potentiometer in a bottom raw. Sometimes it is a note symbol, sometimes it is strange symbols similar to Japaneese character.
If I send MIDI messages more often there are some scenarios:

  • some of smr voice cards stop playing and has all LEDs off or play the note with endless sustain. All the other cards continie to work. After that, all the cards turn off, Ambika resets by itself and it works like it was just turned on.
  • some of voices freeze on one note, but if I turn them off and on in voice menu, they work again. Sometimes all presets becomes empty after that.
  • if there are really a lot of incoming notes and modulations, the display can change all symbols on strange ones (but pushing the swich buttons and changing menu pages helps) or it can freeze at all with no reaction on any pot and button. After that Ambika can reboot by itself or sometimes not.
  • sometimes the crashed cards begin to show “?” In about menu. But after installing it from SD card, it works again.

What I have tried:

  • I read all the topics in Ambika section;)
  • reflowed all suspicious and unsuspicious pads;
  • Swapping voice cards in different ways (jumpers are ok);
  • Changing 6n137, crystall with caps;
  • making a mod with RC network between 6n137 and 644p like it discussed in old thread here;

I use ac-ac 9V 1A adapter, but it gives about 11V AC on a connector. All voltages on refence spots are fine even after crash. All regulators are not hot.

Anyone who had the same experience, please help me in this investigation.

What display are you using? it might be that the character set of the display isn’t matching the standard. I get funny character with the VFD I use and it’s just cosmetic, doesn’t affect the operation.

Have you cleaned off the flux from the PCB? there has been cases where the flux was slightly conductive.

Thanks for the answer. I use display from Buydisplay, it is not fist build with them, previous worked fine.
I used IPA to clean the boards, so there is no flux at all.

Are you using the same 9V adapter for all of them? (the working and non working ones)

My both Ambikas has the same behaviour. With the same adapter.

im having similar problems to you. both in the library page, and when i send over midi cc commands rapidly. happens without voicecards. i noticed the other night that my ac-ac also seems to like to put out 11v if i test straight from the barrel.

i have this wall wart:
PHC AC-091A 9 VAC 1.11 Amp Transformer, 9VA, 2.1mm x 5.5mm Barrel Plugz

Ive fretted over the parts i used, the solder joints, and the pcb, and it doesnt appear i did anything wrong.

I will try to change ac adapter, thank you. What voltage does you adapter has on a barrel?

it’s labelled as 9v, but it appears to be 11v when i test on my multimeter.

Oh, I thought you solved the problem. Now I uderstood.

So I puted 6n137 from another manufacturer and my Ambika was working all the evening without any crash. I will continie to test it tonight.

Which 6n137 brand was causing trouble. And what did you replace it with?

An old one was by Fairchild. But I really don’r know about the new one. Here is the photo of the new one.

Is everything still working nicely with this new 6N137?

Yes, mate, everything is ok with no ussues at all. BTW, I also changed crystal with it.

i ordered one of those exact toshiba 6N137’s to try out on monday when it comes in. I’ll check the 6N137 and crystal separately so that if someone else has this issue, we’re leaving a little more evidence for their message board archaeology.

in that same vane, maybe you should add [SOLVED] or [FIXED] to your title.

Good luck! Let me know about you success.

Changing the 6n137 didnt fix everything, going to throw a new crystal in tonight.

So I tryed to fix the second one and found, that it was crystall issue. I changed it with 18pf caps and everything is ok.

thanks for sharing your troubleshooting!

Swapped the crystal out for another one, no dice. It’s still spectacularly unstable when in the library page, in particular saving and checking the patch versions.