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March 21, 2016 at 8:17 am in reply to: Vintage Micro Synth EH 7000 power transformer problem #121363beatnikParticipant
yeah i thought about the bigger regulators but those won’t fit the circuit board
will try the 100mA ones and hope everything will be fine
March 19, 2016 at 8:06 pm in reply to: Vintage Micro Synth EH 7000 power transformer problem #121358beatnikParticipantI had some further troubleshooting on my micro synth
Basically I found out that the NE5554 regulator was defective and the +12V rail was down to -0.8V
Probably this is what caused the power transformer to melt, because of no protection fuses
Now I have been looking to find a replacement NE5554 ic and they are relatively expensive. About 7 £ a piece
I was wondering if I could save some money by adapting the circuit to a 78L12 / 79L12 pair
My only concern is that the maximum output current for these regulators is 100mA whereas the NE5554 goes up to 300mA
Do you think 100mA would be enough current for powering the circuit ?
March 17, 2016 at 9:33 am in reply to: Vintage Micro Synth EH 7000 power transformer problem #121356beatnikParticipantbrilliant !
thanks ron , you da man !
March 17, 2016 at 9:25 am in reply to: Vintage Micro Synth EH 7000 power transformer problem #121354beatnikParticipantdo you think this one is good ?
is the only one i could find that has the same mounting holes spacing, so i won’t have to drill the chassis
http://www.maplin.co.uk/p/12v-100ma-sub-miniature-transformer-wb02c
March 17, 2016 at 8:37 am in reply to: Vintage Micro Synth EH 7000 power transformer problem #121352beatnikParticipanthi Ron,
thanks for your reply
I am in the UK so in need a 240V primary transformer
I suppose anything with secondaries rated at 24V CT and around 100mA would work ?
February 18, 2015 at 6:30 pm in reply to: Electro Harmonix Electric Mistress repair (polarity fry?!) – hints or tips required! #120545beatnikParticipanti have placed LM741 instead of TL071 and now the pedal works properly again
beatnikParticipantvery likely you have a faulty footswitch. check its operation with multimeter. check also input and output jacks
beatnikParticipantdo you have sound in bypass mode ?
February 12, 2015 at 7:38 am in reply to: Electro Harmonix Electric Mistress repair (polarity fry?!) – hints or tips required! #120536beatnikParticipantcmon man try to fix it. it’s sad to have such a nice pedal collecting dust. to fix the broken trace just use a small piece of wire
i will report if the lm741 fixes the latch up problem
February 11, 2015 at 4:31 pm in reply to: Electro Harmonix Electric Mistress repair (polarity fry?!) – hints or tips required! #120534beatnikParticipantordered one
will keep you posted
thanks
beatnikParticipantsounds like a capacitor problem. try replacing all the electrolytics
if that doesn’t work set up an audio probe and by reading the schematic, follow the audio path and find the stage where the problem happens
keep us posted
beatnikParticipantmake sure you have soldered the battery clip in the right direction or you risk to damage the circuit.
black side goes to input jack ring
then measure the voltage on the ICs and report
beatnikParticipantit sounds like a connection problem. maybe a cold soldering on the pcb. or even bad potentiometer
you should start checking all the wiring and redo the soldering on the pcb
if the problem persists, then you will move on to do some further testing
keep us posted
February 11, 2015 at 8:41 am in reply to: Electro Harmonix Electric Mistress repair (polarity fry?!) – hints or tips required! #120526beatnikParticipanthi everybody
i have found this old thread because i have the exact same problem as the op
my vintage electric mistress had a burnt LM741 in the power supply
i have replaced it with a TL071
the power supply circuit has a latch up problem and only starts working if i measure voltage from 2N4354 base to ground with dmm
i couldn’t find a 2N4354 transistor. I’ve tried both 2N5087 and BC557 but the problem persists
i am wondering what the problem can be. maybe these equivalents are not good ?
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