speak and math only works through power adapter

[analog monster]

I bought a speak and math, thought it was dead so put in an adapter as a last resort and I have life!

it functions completely normally until I take out the power again.  I have tried brand new batteries and I have used my multimeter on continuity test with the two pins at the bottom left of the board where the power lines come in, and the circuit seems to be in tact.  So im a little stumped.

I've done a few bends, but I dont want to bend something attached to the mains.

Any help would be appreciated

[Circuitbenders]

its perfectly find to bend a speak when its attached to the mains via a 6v psu. When people advise you not to bend mains powered things they are mainly talking about things that plug directly into 240v.

If the wiring for the battery compartment is correct and you are actually seeing 6v or so at the board connections, my guess is that theres something wrong with the switching on your power socket that automatically disconnects the battery from the circuit when you plug in an external power supply. There also might be a diode next to the row of resistors at the bottom that might have gone, but i think it wouldn't work with a psu either if that was the case.

[analog monster]

Well I went ahead and tried to fit my midispeak to it, only to find that it wont run from the power jack!

Just tested the voltage, and I'm getting 11.8V from battery.  how is that even possible from 4  1.5v batteries?  Really confused by this.  going to take a look at the diodes tonight, anything else you suggest I look at?  Just to add to the wierdness, sometimes powering up from the batteries will work once I connect and disconnect the power jack, only for it to be glitching or not power at all next time I turn it on.

This is the second speak and math I've bought with a slight fault.  Still fun to bend and play as it will still glitch, loop, distort etc but I really want to have one that will midi-sync with my gameboy :-(

oh and any idea what kind of diode to replace it with?  I have some 6n138's  and  1n4148's  lying around somewhere.

[Circuitbenders]

?  Just to add to the wierdness, sometimes powering up from the batteries will work once I connect and disconnect the power jack, only for it to be glitching or not power at all next time I turn it on.

that would indicate dodgy switching on the power jack wouldn't it? Sometimes it reconnects the batteries when you pull out the jack and sometimes it doesn't.

[analog monster]

could I bypass the power jack somehow?  would just taking it out do or do I need to short two of the three points?  sorry for being so noobish

[Circuitbenders]

assuming you have vaguely the same board as the one i have open here, with the thing face down and the socket on the left the middle point should be connected to the top point internally when theres no plug in the socket. If you follow the board traces back to the battery connection you'll probably find that one of them links to the battery connection and the top point goes off to the power board on the right somewhere. When you insert a plug into the socket the middle point is disconnected from the rest of the circuit so if this switch is broken then the batteries will always be disconnected

You can see if the middle and top points are connected with the continuity tester on your meter, or by looking at the resistance between them. You can just bridge them with some wire for permanent use with batteries but remember to take the link out again if you leave batteries in there and want to use a power supply again.

[analog monster]

nope, the switch did just as you said it should.  diode seems to work, continuity beep only when negative is connected to the band side of the diode.   any other options?  thanks for the thorough walkthru, that was amazingly fast!