Mains Model Electric Mistress 240/18v transformer stockists? hum problem!

[albatross]

Hi , I aquired a old mains model electric mistress and think i need a need a new transformer, as when engaged, the pedal lets off just hum, no other signal but bypasses ok.

I probed around sad1024a with an audio probe, the lfo works, and the ac transformer is still giving out 16volts, so that appears to work but im under the impression the hum is from the transformer. I was told the pedal worked perfect, then he said he plugged it after a few years and this happened.

Also is it normal for this circuit board to have these components? Which look like some form of mods on the back of the pcb.



and a closer look at that:



pic of the board:



Thanks

[StephenGiles]

Try replacing the large smoothing capacitor first, then if that makes no difference replace the voltage regulator just above it - 78L15 or similar. If that makes no difference, disconnect the transformer and connect 3 PP3 batteries  in series as the voltage supply.

[Paul Perry (Frostwave)]

I can't think how a transformer could fail in such a way that it still put out a voltage, but made a circuit hum (that didn't before).
It's difficult to see whether there is AC ripple on the power rail without a scope - but running an audio probe onto it will pick up any hum
that is there.
I'm afraid these units are prone to people plugging in dodgy transformers, usually with expensive results.

[StephenGiles]

I stripped out the power supply on mine and use it with 2 PP3 batteries, they don't last that long but there's no hum!

[albatross]

Hi, thank you very much for the helpful replies
I ve ordered the volatge regulator and suitable cap to replace, i already tried a 16v 220uf cap(low Voltage but...), still the same problem though, if none of that works ill try the battery method.

The loud hum is present almost straight away when probing from the input, but the circuit is hard to follow as it dosent seem identical to the ggg schematic

also the loud hum is almost everywhere in the circuit when probed...

[Paul Perry (Frostwave)]

You know, if the voltage at the input to the regulator (measured by your meter) is 16V, then the 15V reg isn't going to be able to give a regulated output (it needs at least 2.5 or 3 v extra on the input).
But that shouldn't stop the unit working totally, just put hum all over it..
Of course, if the AC tranny is putting out 16AC under load, that is OK - because this will rectify to maybe 22V .. that 16V cap might be in trouble though!

[albatross]

Hi,
I replaced the volatge regualtor and all electrolytic caps, still same problem, i forgot to mention the transformer gets quite hot fast, and the sad 1024 gets hot too, so its probably wrecked....ill try the battery powermethod soon..