I will probably parallel few caps I have laying around to get at least close to 10mf.
The charger is fairly simple,from what I can see it only has a transformer and diode bridge.It's rated for 12A.

 

I have a few stepper motor driver modules, bought to make a DIY CNC machine. All of the installation manuals for the different manufacturers of them agree on one thing, a linear power supply is to be used. They highly recomend NOT using a switch mode power supply for driving stepper motors. Just a transformer, bridge rectifier and smoothing capacitor.

Absolutely! IMNSHO efficiency, compactness, etc... is a distant second to electrical cleanliness and overall reliability!!! --- A decent linear supply (equipped with a 'crowbar') is the only 'way to go' when it (the application) truly matters!

Best regards
HP

 

I will probably parallel few caps I have laying around to get at least close to 10mf.
The charger is fairly simple one,from what I can see it only has a transformer and diode bridge.It's rated for 12A.

Good deal! --- Should you determine that you require regulation, we can help you with that too --- Again, please keep us posted!

Best regards
HP

 

I thought of using lm317 with pass transistor.

 

I'm doubting this is a capacitor problem. In order to isolate it, I'd suggest checking each of the rails (3.3V, 5V, 12V) at various loads and see which fails-- that will tell you whether the problem is on primary or secondary side of T1. If All fail, it's on primary side, if only one or 2 fail, it's secondary.

To be honest, I'd be more inclined to believe one of the BJTs has failed.

 

I thought of using lm317 with pass transistor.

Good idea -- However please bear the following in mind:

1) Operation must be kept within the 'safe area' - else the output waveform will resemble that of a 'blocking oscillator'!

2) It is advisable to protect the output against 'noisy' loads (via 'MOVs', 'Zenmatics', etc...) -- Additionally, a reverse-biased 'fast' rectifier (e.g. MUR1560) across the output is always a good idea!

Best regards
HP

 

I'm doubting this is a capacitor problem. In order to isolate it, I'd suggest checking each of the rails (3.3V, 5V, 12V) at various loads and see which fails-- that will tell you whether the problem is on primary or secondary side of T1. If All fail, it's on primary side, if only one or 2 fail, it's secondary.

To be honest, I'd be more inclined to believe one of the BJTs has failed.

It is indeed rather curious that the loading of a 'slave' channel results in shutdown whereas the 'main channel' appears to function correctly --- How truly a scope would be worth its weight in Au at this point!

Best regards
HP