[Premium-Rx] WJ-8615 Power Supply and Substitutes

[Steve Pappin via Premium-Rx]

SF_SDS60: This is actually a private labeled Astec LPT45 which I tested. The 
+15V and -15V rails are not regulated so they can change by more than +/- 
5%, <14.25 or >15.75V, or with light loads greater than +/- 10%. I measured 
+11.5V with diagnostics on, audio off, all options loaded. My concern is 
that the AUX rails are not regulated or filtered by linear stages. This 
power supply runs cooler because those stages are not present.

The CCI power supply has LM7815 and LM7915 linear regulators. The CMR of the 
linear amplifier bucks ripple. Extra heat is produced due to ripple bucking 
and the voltage drop across the series pass element. Both the original 
MACPOWER and CCI power supplies have linear regulators so the outputs remain 
within +/- 2% and ripple is less than 50 mV at any given time. I measured 30 
mV. Ripple on the LPT45 is OK but higher than the original supply. It can be 
greater than 150 mV depending on how you measure it. In the radio it's much 
lower because of all the added capacitors and filters. On the bench with a 
purely resistive load it's fairly hot.

The Power One MAP40-3003 is expensive but it has linear regulators on the 
outputs. Regulation is tighter and due to the design ripple will be lower. 
Worst case load regulation is +/- 1.75%. I have not tested it yet:
http://www.mouser.com/ds/2/643/power-one_map30-494238.pdf

The effects of changing power supplies and / or parts inside the power 
supply are not always immediately apparent. Some of the 8711 power supplies 
that we worked on had new capacitors installed by someone and they were not 
the right type. They ran very hot! Ripple looked OK at first but as the 
parts heated it got dangerously high. Imagine what that does to the caps 
inside your radio.

WJ-8615 All Versions: I'm in favor of finding solutions that are similar to 
the original design or using the CCI part. I have a quotation from CCI for 5 
piece pricing: $500.00 each. They don't stock PN 481447. It is a custom 
part. This part will work in all versions except the very early D models 
which have the tall fan filter.

Best Regards,
Steve


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