70's atari power supply not working

Checked out those pins and I am not getting the output I should, the voltages are low. I think I will try to replace the rectifier diodes on th pcb on the pwer supply and the big blue cap and see if that helps.
 
HudsonArcade said:
Get rid of the original power supply, bypass the on-board regulators, and put a switcher in in it's place... you'll be much happier in the long run.

The original atari supplies were unreliable and inefficient, and just generate a lot of excess heat.
Click to expand...

I'm strongly against that. It should be kept as original as possible (if possible). You're not putting a modern day engine in a classic car either.

There's also a good chance that the game needs weird voltages that don't come off a modern day switching power supply.

The original Atari supplies were linear power supplies like all of them were in those days. Switching power supplies were new things in the early eighties. Yes, the modern-day switchers are much more energy efficient, but more reliable ? I doubt it. Switchers have lots more parts than linear power supplies (thus more chance of failure), and run under very high frequencies (stressing these parts).

I believe a linear PSU will out-last any switcher easily. All my games run on the original PSU without any problems, but you do have to rebuild them and check for a GOOD PCB/edge connector connection to prevent the sense circuit to up the voltage.
 
Don't worry I won't be replacing the original power supply with a switcher. I tested the voltages at the edge connector and they are low, I replaced the rectifier diodes on the pcb of the power supply and it didn't help, could the Big Blue Cap be causing this issue. Also the the cermamic wire wound resistor on the game pcb is getting really hot and seems to be open but I don't think that would cause this problem. Any ideas why I am getting low voltages to the edge connector? There is a 12 pin molex on the power supply that runs to the edge connector and the voltages all read correct at the 12 pin molex connector.
 
You often get a bit of voltage drop over the wires, especially when they are this old. Is the power supply output adjustable? If it is adjust it to the proper range as read from the connector.

I don't think the big blue is the cause but it wouldn't hurt to replace it. The resistor will get hot, that is why they used a ceramic but it shouldn't test open. In fact, if it is open then it shouldn't get hot at all. Maybe it is opening internally under load. You may want to replace it as well.
 
No the power supply has no adjustments to it, I know that there should be some power drops from the connector through the wiring but it is really low. I am only getting 2.5 when I should be getting 5. As for the resistor it gets so hot that you can touch it, I checked with my multi meter and it shows open.
 
Did you test the resistor while hot or while cold? Like I said, it may open after heating up a bit - it wouldn't be unusual...

If you plan to replace the big blue just replace the resistor at the same time.
 
I don't think I'd alter the circuit that much. That is nearly a 20% change. Stick with something much closer to the 4 ohms and at least 10 watts.

Bob carries these as well...
 
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Just went out and checked the resistor again and now it is showing the proper resistance, like you said if it was hot that was why is wasn't measuring correctly. I checked the voltage at the voltage regulator on the game pcb and it shows 10.64dc coming in and 5.08dc coming out so there does seem to be getting power to the board. Now I am confused
 
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dyno said:
I checked the voltage at the voltage regulator on the game pcb and it shows 10.64dc coming in and 5.08dc coming out so there does seem to be getting power to the board. Now I am confused
Click to expand...
The 10VDC coming in is regulated down to 5VDC - so that part of the operation is running just as it should, so yes, not a power problem but a problem elsewhere on the PCB.

At least you now know that the Transformer is ok, the correct voltage is being supplied to the PCB, and that the PCB is correctly regulating the 10VDC down to 5VDC.
 
Sorry to hijack this thread (kind of) but I have some voltage issues with an Anti Aircraft II PCB which uses basically the same +5V circuitry, so:
I get 18.75 VAC at the edge connector (where theres supposed to be 16.5), then 7.5 VDC after the rectifying diodes.
The LM323 outputs only 3.96 VDC, which is of course too low to fire the game up...
I made a quick&dirty Jamma adapter (just video, GND, +5 V) , connected +5V right at the output of LM323 and board works. Replaced LM323 with a new one and put it back in the cab, but nothing changed.
As far as I understand (I'm not an expert) the LM should output +5V regardless of the voltage going in (within a certain range of course) so 7.5V should be enough? Or am I wrong on this?
What exactly does the 4ohm 10 watt ceramic resistor?
Any idea why I have 18,75 VAC instead 16.5? Should I worry about this?
 
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The LM323 data sheet suggests that the minimum input voltage is 7.5VDC - so in theory you should be OK - although 7.5 really is the bare minimum.

This is a complete punt on my part, but I suspect that the rectifier was designed to output a voltage that is comfortably higher than the bare minimum that the LM323 requires to operate correctly. Perhaps replacing the rectifier diodes might bump up the 7.5VDC and then you might improve the LM323 output.

Like I say though, the 7.5VDC should, in theory, be sufficient. Not sure what else to suggest though.
 
Well I did some more poking around on the board with the multi meter and where I am suppose to be getting 25vac coming in I am only getting 12.5vac, and there is one pin that suppose to have 25v also but I accidentally touched the trace next to it with the probe and now I am getting 0v from that pin on the edge connector. Any ideas where to start figuring the voltage drop and loss? I am getting just over +5vdc on the board so it is getting power but still it seems dead, I was thinking of changing the 6502 microprocessor chip to see if that is the problem.
 
Are you sure you are reading the right pins?

The input is 25VAC Centre Tapped (25VAC CT). A centre tapped voltage uses 3 rails (wires if you like) rather than 2. If you read the 2 outer rails you'll get 25VAC. With a centre tapped AC voltage, if you read from either outer rail to the centre rail you'll get a reading that is half of the AC voltage. Which in your case would be 12.5VAC. Which is what your multi-meter is telling you you've got.

I therefore suspect that you might be taking readings from the wrong pins. This might also account for the zero reading you seem to be getting elsewhere. Check which pins you are using carefully, against the schematic, and see how you get on.

Anyway - the 25VAC is used only for sound in this game - so poking about with this set of voltages isn't going to help you get the board up and running.

Good luck!
 
I am pretty sure I was reading the right pins, the pins are Y, X, and W if I remeber correctly. Thanks for the info on the center tap, I wasn't aware of that and I wasn't sure what CT meant. I will poke around some more and let you know how it goes.Thanks:)
 
Not having much luck with the pcb, there doesn't seem to be anything that is obvious. The only thing is the 4ohm10w ceramic wire wound resistor gets smoking hot which it probably should be. I have started a new thread since this is a pcb issue and not a power issue anymore. Thanks for all your help:)
 
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