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Thread: IMSAI 8080 Power supply issues - i think...

  1. #31
    Join Date
    Jun 2012
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    Livermore, CA
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    My bad, sorry. I realized what I had done as I was falling asleep last night. 120 hours seemed a bit off to me.
    Checking DC. Now up to 5v, 1v /hr. The caps are all cool. The fan started to turn at about 4v dc. so far so good.
    Thanks
    Atari Falcon030, Atari MSTE, Atari PS3000, STACY 4, 4160STE-CosmosEX, Atari PC1, 400/800/1200XL,800XL,800XE,130XE, XEGS, Apple IIGS, TRS-80 4P, TI 99/4A, Co-Co 3, Amiga 500, C64/128D

  2. #32
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    Oct 2016
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    Dutchess County, New York, USA
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    Quote Originally Posted by Dwight Elvey View Post
    That supply was suppose to run on a 5 amp fuse for 120V and a 2.5 for 220 wiring.
    If you'd like to bring up the caps slowly, you can use some resistors but that will require removing them from the PC board for the plus and minus 18V caps. The 8V line, we can unbolt the 4 diode studs and put a resistor in series one of with them. If you remove the 18V caps, use a sharpie to mark both the board and the caps so you'll get them back in the right place and oriented correctly. You know something like a stripe down the side and onto the board for one and two stripes for the other.
    For the 8 volt line, I recommend using a 2K resistor.
    For the other +/- caps, you can put a series resistor for bot of them of 4.7K. You'll need to run wires for these two. Make sure to match the polarities to the what they ar in the board. You can use some nuts and bolts to make the wire connections to the board. If you do it this way, you shouldn't need any series limiter to the primary. Check the voltage every no and then. When the 8V cap reaches 5V or so, you should be safe to install it.
    For the +/- caps you'd like them to be about 10 or 12V.
    It may take an hour to a couple days, depending on the state of the caps.
    Dwight
    Dwight, I see you take a lot (whole lot) longer reforming cap's than what I've done in the past. Might be why I've had problems?
    Crazy old guy with a basement full of Pentium 1 laptops and parts

  3. #33
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    Jun 2012
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    Livermore, CA
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    I am back to this.
    I have been very very slowly raising the voltage over the days since my last post. I often forget to go out to the garage and bump it up a bit. But now I'm at a full 120vac going it. I have never power it down. Nothing is warm or hot. But it is warmer then the room temp, so I do not think there is a heat problem.
    The connections on top of the bus-board are showing 10.56vdc, an 19.53vdc. Looking back on posts, they should be 8vdc, & 18vdc. Could this because there is nothing on the bus-board drawing/using power?
    Thoughts, suggestions.
    Atari Falcon030, Atari MSTE, Atari PS3000, STACY 4, 4160STE-CosmosEX, Atari PC1, 400/800/1200XL,800XL,800XE,130XE, XEGS, Apple IIGS, TRS-80 4P, TI 99/4A, Co-Co 3, Amiga 500, C64/128D

  4. #34

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    Quote Originally Posted by KLund1 View Post
    I am back to this.
    I have been very very slowly raising the voltage over the days since my last post. I often forget to go out to the garage and bump it up a bit. But now I'm at a full 120vac going it. I have never power it down. Nothing is warm or hot. But it is warmer then the room temp, so I do not think there is a heat problem.
    The connections on top of the bus-board are showing 10.56vdc, an 19.53vdc. Looking back on posts, they should be 8vdc, & 18vdc. Could this because there is nothing on the bus-board drawing/using power?
    Thoughts, suggestions.
    It is lightly loaded so those values are not out of order. Did you get the 5A fuse?
    Stick one board in at a time. Listen for pops and other bad sounds. Measure the voltages on the outputs of the regulators. You should be able to find the outputs, they only have 3 leads. They have input, ground and output. Most cards will likely have only 5V regulators but a few will have +- 12 V as well.
    If all is happy, start with only the CPU and one RAM card. With that you can look at the front panel.
    Dwight

  5. #35
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    Jun 2012
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    Livermore, CA
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    Here is the CPU card.
    There seem to be two missing IC's on the lower left of the card, LS75's.
    Also in the 2nd column from the left the second IC down from the top of the card has pin 11 not in the socket, it is an S132.
    I wanted to check these with you before I put in.
    Thanks
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    Atari Falcon030, Atari MSTE, Atari PS3000, STACY 4, 4160STE-CosmosEX, Atari PC1, 400/800/1200XL,800XL,800XE,130XE, XEGS, Apple IIGS, TRS-80 4P, TI 99/4A, Co-Co 3, Amiga 500, C64/128D

  6. #36

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    I am not familiar with this board. There were a number of Z80 boards created to be able to connect to the IMSAI and ALTAIR front panels. This looks to be one of them. It looks to be able to have a boot ROM as well. Without a schematic, I couldn't tell you much more.
    Dwight

  7. #37

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    Here is a manual:
    https://www.hartetechnologies.com/ma...r%20Manual.pdf
    It shows that there is a cut needed if the from panel generates MWRITE, which the IMSAI does. This might be the lifted pin?
    The 2 LS75 are used to capture interrupts. If your system is not going to use interrupts, you can leave these off.
    You might want to might want to study the manual.
    Dwight

  8. #38
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    Jun 2012
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    So far so good. I have put 3 cards in. CPU, & 2 mem cards. no pops, hiss, etc. I get 9.9vdc on the regulators I can reach easily from each card. They have been powered for about 2 hours.
    Should I put the front panel card in?
    Atari Falcon030, Atari MSTE, Atari PS3000, STACY 4, 4160STE-CosmosEX, Atari PC1, 400/800/1200XL,800XL,800XE,130XE, XEGS, Apple IIGS, TRS-80 4P, TI 99/4A, Co-Co 3, Amiga 500, C64/128D

  9. #39

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    Yep, go for it.
    Although, I really expected you to also measure the regulators outputs.
    Dwight

  10. #40
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    Jun 2012
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    Livermore, CA
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    All good so far. Installed all cards one at a time. Nothing popped! The computer appears to boot a program from 1 or more cards. I see the LED blinking for a while then settle in a repeating pattern.
    Working on cleaning to the dual 8" drives for it. I got a WSYE Ny-60 screen and keyboard, and another keyboard(mush older) I think that goes with it. I'll try them and see what I get.
    Atari Falcon030, Atari MSTE, Atari PS3000, STACY 4, 4160STE-CosmosEX, Atari PC1, 400/800/1200XL,800XL,800XE,130XE, XEGS, Apple IIGS, TRS-80 4P, TI 99/4A, Co-Co 3, Amiga 500, C64/128D

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