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Atari xevious


cal2

Question

Hello,

 

I will soon receive a xevious pcb from atari I won on ebay for $25. According to the seller it runs through the test patterns then says rom error 7.

 

I hope it will not be a to complex repair.

 

While looking to make a jamma adapter for it, I found on mikesarcade.com that pin E (components side) needs 10.3 VDC UNREG. Do anyone knows what this exactly means ? Will 12v be ok ?

 

thank you,

david

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The error could be a faulty rom or something far more complex.

 

Yeh - the ROM test actually tries to trigger the system to provide data from the ROM, the test then mathematically calculates if what it was given adds up to what it was expecting, if it isn't then you get the ROM error. It could be the ROM at fault, but it could be the data bus, the buffers, the address decoders, or even the circuitry that activates the ROM. In my experience its usually the logic that controls the ROM, rather than the ROM itself.

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if it wants 10v unreg and you give it 12v regulated you are likely to fry something. If it feeds a regulator then it will get very hot, if it is feeding something directly then there won't be the volt drop it is expecting and it will be caned with a consistantly too high voltage. You need to find where that line goes and what it feeds.

 

If you take a mains transformer, and rectify the output to DC, which is what happens in a very basic power supply, the voltage you get depends on the current you draw, with no load the PSU may put out 15V, attach a 500mA load to it and that will fall to perhaps 9V (pulling figures out of my arse here).

 

Regulated powersupplies have voltage regulators in them that will consistantly provide the voltage they are designed to put out, with no load a 12V vReg will put out 12V, add a 250mA load and it gives 250mA at 12V, up the current drain to 500mA and it gives 500mA at 12V. You just have to give the vReg a fair few volts more than you want out - the excess enegry is bled off as heat.

 

An unregulated PSU would deliver the current but at lower and lower voltages.

 

So if that 10V line is feeing a regulator and you feed it a regulated volatage source, if the difference in regulators is great then you end up with a lot of heat to get rid of.

 

If that line is feeding something downstream then that device will have voltage requirments and will exert a current drain on the PSU, as unregulated is specified and its a weird number I would expect that the designers were using the voltage drop effect to give the right voltage when that device exerts the current draw. So 10.3v unreg may well fall to 9v when everything is connected.

Edited by Womble
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