Old Napa Battery Charger Problem

[Farmall 1066]

My ancient Napa 85-140 battery charger has apparently died. On 12v low, it has about 9v output, 11.5 on hi and 12.8 on boost. 6v functions are all low also.
Has ampereage enough to spark nicely, and ammeter shows output, but voltage is low.
I can see AC voltage change at rectifier inputs as switch is turned, so I think switch and transformer are ok. Connections are all good, and nothing looks or smells burnt.
Can a rectifier fail partially? I'm at a loss as to what else this could be?

 

[geartow]

Are those voltages with the meter on charger? And are you measuring them under load!?

 

[Farmall 1066]

Those are open circuit voltages, measured at the charger leads.

 

[Warrenator]

Might be some insulation has failed on the windings of the transformer, take a peek at the condition of that.

My old NAPA charger that came with the house had been left out in the rain, the alligator clamps were so corroded (rusty, just steel plated with copper) that they would heat up and smoke. Check the condition of all your wiring, high resistance would cause low voltage as well.

 

[redmondjp]

Yes, you could have lost one of the rectifiers. Do you have an AC voltmeter that you can use to check its output?

 

[Infinia]

is that a selenium device ?
put a modern rectifier on it> at least something silicon.
added link

 

[engineer2]

When I was involved in that decades ago, failed rectifiers were the most common thing to replace. As said, check for AC in the output. An oscilloscope is the best way to check it.

 

[Farmall 1066]

is that a selenium device ?
put a modern rectifier on it> at least something silicon.
added link

Idk what it is. Lol.
Took apart the plates, and one was shorted.