Atari 5200 PS Voltage - Indus GT Replacement

[WildBill777]

So I picked up an Atari 5200 PS to use as a replacement for a failed Indus GT drive power supply.

 

I'm reading around 14.4V from the plug with no load.  Supposedly this is a 11.5VDC power supply, is that a safe voltage reading with no load?

[TGB1718]

Under no load conditions, some regulators don't output the correct voltage, do you have something

like 100 to 200 ohm resistor you could put across the terminals and measure across the resistor,

it doesn't take much current flowing to get it to regulate correctly.

[cwilbar]

I am using a 'modern' 12V PSU on my Indus.  I've had no problem with 12V so far.

Looking at the Indus schematics, they have 2 12V rails, one unregulated (straight from the external supply), and one with a 12V 1W Zener diode.

If 14.4V in results in that zener trying to dissipate more than 1W, it will take out the zener.

The 7805 regulators can take up to 25V input.  Though, the more input, the more load on the part and heat generated, but it would be within spec

The drive motor runs off the zener regulated 12V, plus it uses a tach signal, so speed regulation should be fine.

 

Others may be able to comment further, but myself, I would go with a 'modern' 12V regulated switching supply or an original 11.5VDC.  14.4V 'feels' on the high side to me, but it should work.  The question would be the stress on the zener, the regulators, and anything that might be powered off the unregulated rail (if anything).

 

 

 

[WildBill777]

Any recommendations or links to good modern power supplies for the Indus and for the rest of the Atari line for that matter?

[BillC]

8 hours ago, cwilbar said:

If 14.4V in results in that zener trying to dissipate more than 1W, it will take out the zener.

According to the schematic there is a 22 ohm resistor before the zener diode, it would only take 109mA of current to create the drop from +14.4V to +12V.

[cwilbar]

5 hours ago, BillC said:

According to the schematic there is a 22 ohm resistor before the zener diode, it would only take 109mA of current to create the drop from +14.4V to +12V.

There you go ? ..... I was too lazy to look up and compute the math ? ....

 

[+slx]

16 hours ago, WildBill777 said:

Any recommendations or links to good modern power supplies for the Indus and for the rest of the Atari line for that matter?

A lot of portable 3.5“ hard disc (enclosure/case) PSUs have the required 12V/2A and some even have the correct plugs. Those are often available cheaply. 

[cwilbar]

On 5/6/2022 at 11:01 AM, WildBill777 said:

Any recommendations or links to good modern power supplies for the Indus and for the rest of the Atari line for that matter?

For Indus it should not be hard to find a modern 12V supply cheaply with the right connector on it.

 

For Atari XL/XE you can use a modern 5V supply (but need to change out the connector for the DIN connector).

 

For 400/800/1200XL/810/1050/850/etc Atari used a 9V AC supply (most common is the 31VA one).  There are fewer options here, as you can't make advancements in a transformer and fuse assembly (which is all that Atari power supply is).  The Atari ones are robust, there is really only a fuse to fail (other than a lightning strike, doubt much else could take out the transformer).