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Thread: Imsai 8080 power supply question...

  1. #1

    Default Imsai 8080 power supply question...

    Hello.

    I bought an Imsai 8080 on ebay last week and i have to wait a few weeks to get it. So, i am in germany and as you know, we have 230V @50HZ. Now, i have to fix the problem to get the imsai running on 230V. I have read in the imsai manual, there is a power supply with the possibility to change the primary voltage to 230 V. Please take a look to the picture from the mounted psu. Is this the version with option to play with 230V ??

    s-l1.jpg

    s-l1600.jpg

    thx

    Jan

  2. #2

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    You need to take a couple pictures showing the bottom left of the transformer, as seen in the first picture. We need to see if the primary has a split winding. If not, you'll need some way to reduce the voltage, such as a variac, auto transformer or 2:1 transformer.
    Also, running on 50Hz, the transformer may get hotter, so that is something you'll have to watch. The filter capacitors may not be sufficient as well for 50 Hz. Do you have an oscilloscope or access to one?
    Dwight

  3. #3

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    It looks like you have a CPU board and what looks like a EPROM programmer ( likely for 2708's ) The board in the middle is in question? I'm not sure what it is.
    Dwight

  4. #4
    Join Date
    Jun 2012
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    Default

    As Dwight has stated - it all depends upon the transformer you have fitted to your machine. Back in the 'bad old days' they would generally fit what was available at the time; so your specific transformer may - or may not - be changeable...

    I have the odd machine at home that I could change from 110V to 230V operation, but I have made the conscious decision to run them off a 230V to 110V step down transformer. This is to give me the best margin for the front-end X filters that are fitted to these machines. Something worth thinking about (if they are fitted to your equipment).

    Dave

  5. #5

    Default

    ... and what looks like a EPROM programmer ( likely for 2708's ) ...
    Based on the socket locations, toggle switch and the discretes, that sure looks like an SSM PB1 - 2708 / 2716 Programmer & 4K / 8K EPROM Board.

  6. #6

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    Yes, this is the eprommer SSM PB 1 2708/2716 Programmer. And 16k static ram board and active bus terminator. Yes, i have 3 different oscilloscopes That´s no problem. I have seen in manual, with 50HZ i should go 1 step down under the wished voltage.

    THX

    Jan

  7. #7

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    @daver2: You are in UK, so you have 240V AC. Which step down transformer do you use exactly ?

    @all: If i woould have the imsai universal psu and i would replace the old parts on psu to new parts..except the transformer itself..then, it should work fine ?! How do you think ?

    THX

    Jan

  8. #8

    Default

    Did you look to see if it was a split primary?
    Do note, do not use one of those small adapters you see for tourist. You'll know it looks right if it is really heavy ( meaning it is a transformer inside ). Still, looking at hardware stores near airports may have better results.
    It will need to hold at least as many amperes as the fuse is rated for. If it is an auto transformer the physical size is about 1/2 the volume of the one you have. This is because the core only carries 1/2 the current. A trandformer needs to be the same size.
    You might look in older electronic equipment as well. Those with transformers often came with split primaries. These can be used as an auto transformer easily. I used one in the USA that needed 240V and the line was only 110V. I bought a 18V filament transformer. That gave me 238V ( close enough to run a mass spectrometer made in England ). I used the split primary to get 220V and the filament winding to bring it to 238V.
    Dwight
    Last edited by Dwight Elvey; May 21st, 2019 at 03:04 PM.

  9. #9

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    I have only these 2 pictures from psu. The Imsai is not on my home, it is on ship between USA and Europe.. I bought it last week on ebay. But you know, when i´ll get it, i want to start with it directly...

    Jan

  10. #10

    Default

    In the other post, I forgot to note that the Poly video board can be jumpered for 50Hz displays as well.
    Dwight

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