I have a schauer 12v battery charger

The charger is a 2 amp trickle-12 amp charge-50 amp start. DC output is only 11.8 - 12.0 it has a start duty of 3 seconds on , minimum 3 minutes off. but when trying to charge a battery it is on 3 seconds and off maybe a minute and back on again and there is now battery draw at all. I would like to repair it if i can find parts and find out what the problem is. Schauer model#J512 . If i caint find the exact parts maybe the original parts can be replaced with parts that work. Help

I have a 2/12/50 amp car battery charger. when i test the DC output i am getting 11.8 - 12.3v. When i connect to battery to charge it the meter shows about 3amps then it goes to zero and then back to 3amps and it does that for a while till it stops all together and i have to unplug it for a long period of time before it resets
What i would like help with is troubleshooting this unit and doing a repair. But i am not sure where to start. There are no numbers on the transformer or the copper plate the diodes are mounted in or on the diodes.
These are some pictures for reference.

Hi.
First, read its user manual, and its working principle if available.
Then, make sure it is not working as expected.
When more doubts, call the manufacturer customer support.
If all fails, obtain/draw its schematic and post.

Mine does that when the battery is unchargeable/bad.

Thats what i was kinda figuring and the battery i was trying to charge was a reconditioned battery

The company that made this charger is out of business and the company that bought all spare parts and anything related does not have anymore parts or anything for it. Is there anyway i could maybe get the schematic?

Some times you get lucky by Googling the model number and make, but not always.

Try a known healthy battery. Modern battery chargers have implemented some sensing 'brains'. Trying to resurrect a defunct battery will not work.

Thanks I will.