RipMax Pro-Peak Repair

[NeilP]

I have one of these PSU's and it has died.
I was going to dump it as I do not really need it, but I may come in handy, so I thought I would have a go ...and no lose if I can't. Doing it more out of interest and learning than real need for it

In use, it started buzzing, then buzzing got louder till it stopped working, no smoke or smells.

I have google d them and they do seem prone to failure, but have not yet found any thing more than that...was hoping for a thread like..."It is a common fault, and it is XYZ that blows"
But no luck.

So what to look for, where to start...go it opened and no blackened components...going to take the board out next so i can get to the back but not sure what then to start checking

Any clues?

 

[heathyoung]

Test the usual - large semis (ie. totem driver transistors) with a diode tester, check that the small stuff is powered (like the TL494). If its a bootstrap design, check your startup cap (a small 50-100v electrolytic - usually under 10uf or so) - replace it.

 

[NeilP]

Ok , thanks

There is pwr as far as the initial pair of NPN power transistors, and that is where I stopped yesterday. I pulled out. data sheet for them , ID'd the pinout
I did check while they are on the board with a diode tester, across Collector Emotter junction of each one, but was not sure of two exactly what the rexults should be and if the results will even be valid while tested in circuit

Across the C-E junction, the diode tester showed conduction in one direction of about,. umm cant be sure now but, 0.505 and infite in the other.
Now here is something I am not sure of, when in diode test mode, what is A DVM. displaying?? Is it resistance or voltage drop across the junction?

Not sure on what OCP system it has, but will check and see if I can trawl up any kind of datashedt for them.
I found the Ripmax website, and a UK Phone number for them, but no E-mail. Yesterday was a public holiday in UK, so will try phoning them tomorrow and see if I can get more info from them

Will check out the pwr to the 494 tomorrow and see if that is getting power


Thanks for the help

Neil

 

[amberwolf]

The buzzing is usually the transformers or inductors physically rattling as the current is switched in them. When the capacitors are working right, they don't do this as much, because the ripple currents are kept lower by the caps.

When the caps fail, which is very common as electrolyte evaporates in the hot environment of a PSU, the buzzing gets louder becuase the current flow increases, physically moving the stuff in the magnetic fields farther each cycle, and pushing harder, in the inductors or transformers in that current path.

At some point, it's too much ripple, and something gives. Usually a power semiconductor, like the driving stage for the main switching transformer, or one of the output stage controls, due to voltage spikes from too little filtering.


If the buzzing was the same frequency as your line / wall voltage, a low frequency tone, it is probably on the input / mains side where caps failed.

If it was a higher frequency, it is probably on the output side or driver stage.

 

[NeilP]

Ah ok, too bad I dont remember, it was months ago it died

 

[NeilP]

OK, so here is where i am at

the first two transistors appear to be 2SC3306 NPN

like
http://szmjd.en.alibaba.com/product/295372801-209496477/Transistor_2SC3306_C3306.html

there is no voltage at all at any of the pins of the TL494

There are a 5 of the 4.7uF electrolytics and all look ok externally..where is the startup cap likely to be located..Would it be one of the ones near the transistors with no heat sink in the picture

The transistors both test the same..this is NPN ..and the transistors in circuit

With DVM in Diode test function
Base to collector conducts with test leads in both polarities...reading of zero in both directions

Base to Emitter....
negative test lead at base 540 on DVM
Positive at base....1 no conductivity...open circuit

Collector to Emitter
negative test lead at collector 540 on DVM
Positive at collector....1 no conductivity...open circuit

It seems that you may be correct in the idea that it is the start up capacitor...or the transistors..there is no voltage of any sort on the other side of any of the transformers.

I am assuming the first pair of power transistors are set up to oscillate? and produce a pulsed DC to the transformers? and since there is no oscillation..the transformers are not powering up the other side of the board. I may try and scavenge some transistors off some old PC PSU's tomorrow and see if I can swap a few of the caps out an see what happens