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Transformer gurus help....


raysco

Question

Hi Gurus,

I have been looking for a power transformer for my Atari Middle Earth, (I know you are asking why).

I am tracking one down but also want to investigate alternatives.

I need 5 outputs, I know I can get a 5v logic from a PC supply, so only 4 required.

Solenoids are a 40v AC tap on a 15A fuse to a bridge rectifier.

 

 

Lamps are a 17v AC on a 15A fuse to a bridge rectifier.

Audio is a 16v AC on a 2A fuse

I think I can get the above from a 24v AC transformer and modify the output.

 

Lastly is the one I'm more not sure of, the displays on this run off a +90, -90v AC centre tapped transformer output, I have googled to no avail but I may be searching for the wrong terms.

 

From one transformer I am happy to put in 3 or 4 if required and then tie them together as necessary in the schematics.

 

Anyone have any info, thoughts, ideas, links....except "don't bother"

Cheers

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Probably handy to know what DC voltage you get after the bridge rectifiers for each circuit. That way you could use two 24vAC transformers wired in series to get 48vAC for the solonoids. You convert that to DC and then you can regulate that down to your other DC voltages you require after each voltages Dc conversion. Two 24v tranys in series is only required if you want to use the original coils, how about swapping them to Williams or Gottlieb coils then you only require one transformer. Something to think about.

 

The +90DC /-90DC is going to be a bit harder. Not the +90, the -90 is the hard part. Have a look how Williams and Bally got this same required 180volts potencil for there displays might be a good starting point.

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Probably handy to know what DC voltage you get after the bridge rectifiers for each circuit. That way you could use two 24vAC transformers wired in series to get 48vAC for the solonoids. You convert that to DC and then you can regulate that down to your other DC voltages you require after each voltages Dc conversion. Two 24v tranys in series is only required if you want to use the original coils, how about swapping them to Williams or Gottlieb coils then you only require one transformer. Something to think about.

 

The +90DC /-90DC is going to be a bit harder. Not the +90, the -90 is the hard part. Have a look how Williams and Bally got this same required 180volts potencil for there displays might be a good starting point.

 

Yea, I thought the 24v AC might be the way to go however I'm not sure what the expected DC voltage is, I would have expected it to maybe 12 for the audio rectified on the audio circuit,but I can't find it anywhere in the service manual.

Also maybe I could modify for 24v coils which would be OK.

 

Williams Flash has +100 -100 maybe that could be used?

Thanks @Autosteve Just looking for hints and suggestions, some nice ones here :D

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The audio may also be 18vDc. You could put into the audio board the required 16vAC using a plug pack, yes they do exist, and then measure what DC voltage is coming out further on the audio board.

 

Yes Williams has +100 -100. You can use zener diodes to drop that voltage down both on the plus and minus side exactly as they did but you still require the high AC voltage to start with.

 

Have a good look at how Williams gets it voltages required because they are not far off what you require. You could just be looking for a much easier to obtain Williams SS transformer to get your machine running and then you use Williams coils or convert your Ataris coils to handle the lower 28vDC. At least then you are using common Williams coils rather than hard to get Ataris. I don't think it would be a step in the wrong direction myself.

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The +90V and -90V will be generated by the power board

The transformer will only put out 90VAC

This voltage is very low amperage so you could use a 240 to 100 step down from an arcade monitor

I think you will find that the power board will regulate it to the required 90V

 

I would not recommend using too many transformers in series, you will get too much loss.

The coil voltage is the voltage that is going to take the longest to get right, if the transformer isn't big enough the coils will not have enough guts to run properly.

 

I have done exactly what you are doing on an old Stern once before, it takes a fair bit of messing around and a lot of transformers on hand to test and try again.

In the end I got it just right and the solenoids were actually a little bit snappier and the game played better than standard.

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image.thumb.jpg.af36a8476ed5b1f1d626ce5612a7d054.jpg

 

Yes @Boots just looked at it further and you are correct, the transformer output is actually 170vAC with a centre tap, the Auxilliary board creates the +/- 90v which is only used for the display power.

I will take a look at how Williams created their outputs as suggested by @Autosteve.

 

Hopefully I will be able to get the correct part :)

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