smr4 no sound - cooked IC's?

hey peeps, finished assembly of shruthri, but getting no sound from filter board. control board signals it is getting midi (LED 7 blinks slowly when note on received), and i get the unfiltered synth sound when i connect the OSC and GND pins to the mixer. so far Ive got to point 3 in the troubleshooting guide, where no audio is returned (1 pole filtering). next step is to start swapping IC’s,
BUT
the 7.5v, 300mA power supply i was using got ‘borrowed’, and i switched to a 9v which turned out to be delivering 500mA - when i checked the power supply diagnostic with this new power supply, some of the voltages were +/- 6.6 volts - DOH!
Ive read that this voltage may well have damaged some of the board components - can someone advise which components are likely to have been damaged, so i can start by replacing them? Any help or suggestions gratefully received, especially considering this is my own stupid fault…
:-/

you have a bipolar supply? that’s very rare if it is DC.

very rare, and available to swap for a working smr4
:wink:

just been over the board again, resoldered a few suspect connections. now getting good output from 2 pole filter (troubleshooting point 4) and some output from the jack connection, albeit quite hissy + quiet. should i be able to change patches without the LCD connected, or can you just get the one patch?

You should be able to use every single function of the shruthi (or those that you have soldered at least) without a display… :slight_smile:
The negative voltages were probably you using the probes the wrong way round :F

You won’t fry chips on the analog side with tensions such as ±6.6v.
I think that they can handle ±12v without a problem.
But on the other hand, the chips on the digital board won’t handle +6.6v… and this measurement is very surprising, it’s quite unlikely that both regulators are faulty, especially with this behaviour.

So at first, check that your DC adapter is really a DC adapter, and that it’s really supplying more than 7.5v DC.
There’s no problem putting the screen in place if you are 100% sure that the control board power supply is really +5v, if you have sound at the OSC pin (with a very strong volume level) and if the switches and leds react properly. Actually, having the screen in place will help you debugging the filter board. Before you put the screen in place, you should ensure that MIDI connectors are really well aligned, and that every component leg is well trimmed under the screen location. “Cleaning” it with a toothbrush is not a bad idea either.

many thanks guys.
:smiley:
im so close i can taste it!