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Thread: Cromemco 8K Bytesaver transformer question

  1. #1
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    Default Cromemco 8K Bytesaver transformer question

    Might anyone know anything about the little pulse transformer on the Cromemco 8K bytesaver? Who made the transformer or specs?

    It's used in the step up inverter circuit for the programming voltage. It's listed as an XT8K on the parts list. I google and find no information. I'm repairing a Bytesaver that is missing the transformer.

    Cheers,

    len
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    Does anyone have a Bytesaver, any model, that they can look at the XT8K transformer and tell me who the manufacturer might have been?
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  3. #3

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    Most such coils were wound to a specification. There would be a turns ratio, the core saturation level, inductance of the coil and wire size. I have a 8K board but it is in storage. I doubt you'll find it today. My guess is that it was a 1:1 transformer, used in a flyback mode to get the higher voltage.
    Dwight

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    Thanks Dwight,

    I'll start with a 1:1 and prototype up the circuit and see what I get out of the convertor.

    Thanks.

    len

    Quote Originally Posted by Dwight Elvey View Post
    Most such coils were wound to a specification. There would be a turns ratio, the core saturation level, inductance of the coil and wire size. I have a 8K board but it is in storage. I doubt you'll find it today. My guess is that it was a 1:1 transformer, used in a flyback mode to get the higher voltage.
    Dwight
    Spread the joy of Vintage Addiction

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  5. #5

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    Quote Originally Posted by 8008guy View Post
    Thanks Dwight,

    I'll start with a 1:1 and prototype up the circuit and see what I get out of the convertor.

    Thanks.

    len
    I was looking a the schematic. It looks to have at least one separate winding and one center tap.
    It might be easier to make a three winding 1:1:1 work. One might consider winding ones own on a core.
    Dwight

  6. #6

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    I looked at my Bytesaver II and the coil is labeled “CROMEMCO XT8K A”. So yes, as Dwight mentioned, looks like it was a custom wind for Cromemco.

    Mike

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    Thanks guys. I have a bunch of cores around from when I was designing a switcher, although they are a bit large. In any case i should be able to wrap up something for a test.
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    If you get nowhere on the transformer, you might consider substituting one of the little step-up adjustable switchers. They're tiny and can deliver up to 35VDC--and tiny and cheap.

  9. #9

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    Looking at the schematic, I'd say 1 & 4 are the feedback. 3 is the bottom of the output coil, 2 is the center ( may be offset towards 3 ) and 5 is the top of the coil.
    3 and 4 could be swapped but it makes little difference.
    Dwight

  10. Default

    Quote Originally Posted by Chuck(G) View Post
    If you get nowhere on the transformer, you might consider substituting one of the little step-up adjustable switchers. They're tiny and can deliver up to 35VDC--and tiny and cheap.
    Back in the day, I had a Solid State Music programmer. I was running dozens of EPROMs through the UV eraser and the programmer each week to support our Pro-Comp systems out in the field, as well as new orders. At some point, the programmer died. It had to go back to SSM for repair. Fortunately, I had enough already-programmed parts to hold me over until it came back. There was some TI switcher-on-a-DIP chip used to generate the programming voltage. Things worked fine for a while, until the same thing happened. I looked at the chip and it had melted - apparently I had a bad 2716 EPROM (out of hundreds). I wasn't about to scrap every EPROM, so I hooked up a nice Lambda 50A rackmount adjustable power supply (which conveniently fit in the rack below the TEI chassis that held my programmer) to the appropriate place on the SSM card. Programming went fine until a couple months later, when I tried programming an EPROM that came back and there was a loud "Blam!" as the glass erasure window blew off the part and went flying across the room. I'd found the defective EPROM.

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