Home › Forums › Vintage EHX › Vintage Micro Synth EH 7000 power transformer problem

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  • March 16, 2016 at 7:15 pm #84317
    beatnik
    Participant

    Hi everybody

    my vintage Micro Synth – first version EH 7000 – has stopped working. No sound at all

    I have some knowledge in pedal repair so I opened up the unit and while i was taking voltage measurements i noticed the power transformer got very hot and started to make sizzling noise !!!

    i disconnected the transformer from the circuit but still it was frying like a steak on a grill !! – i guess it’s definitely gone south

    I am wondering what are the specifications for the power transformer, the schematic doesn’t provide that information

    The circuit runs on +/- 12V that are regulated from a dual secondary transformer by a NE5554N chip

    Please let me know if you have any suggestions in finding a replacement

    If somebody has an original spare part and wants to sell it that would be great !

    March 17, 2016 at 12:02 am #121351
    The EH Man
    Moderator

    This one will work fine.

    http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMv4oUrzpPKU3ByqNvysmkwGIQXFwlz1KSg=

    March 17, 2016 at 8:37 am #121352
    beatnik
    Participant

    hi 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 ?

    March 17, 2016 at 9:24 am #121353
    The EH Man
    Moderator

    That would work.

    March 17, 2016 at 9:25 am #121354
    beatnik
    Participant

    do 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 9:29 am #121355
    The EH Man
    Moderator

    That should be fine.

    March 17, 2016 at 9:33 am #121356
    beatnik
    Participant

    brilliant !

    thanks ron , you da man !

    March 19, 2016 at 8:06 pm #121358
    beatnik
    Participant

    I 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 20, 2016 at 3:28 pm #121359
    Scruffie
    Member

    100mA regulators will be fine, although if you have any concerns you can use 7815 and 7915 which are both spec’d for 1A of current.

    March 21, 2016 at 8:17 am #121363
    beatnik
    Participant

    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

    November 22, 2019 at 9:57 am #125655
    acobberson
    Participant

    Sorry to dig up an old thread, but I’m also repairing an original micro synth.

    Is it possible to simply bypass the voltage regulation circuitry and simply feed the unit with 12v? Seems like a quick cheap fix. I’ve done that with an old Polychorus, but from what I remember that pedals transformer rocked it down to 12v already. I’m not real concerned with keeping the unit “original” as it is pretty well used. The convenience of using a power supply outweighs the “keep it original” voice in my head.

    Thanks!

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