Oltronix B32-20R Repair attempt

[halexa]

Hi all,

Got hold of a broken Oltronix B32-20R power supply. The unit blows the mains fuse on power on. I suspect that the transformer is the culprit. Between pin 6 and 7 on the transformer mains input  it only read 0.2 Ohm i suspect that is not OK, but my knowledge in transformers are not 100%. The transformer is setup for 220V and i removed the jumper wire between pin 7 on the two transfomers before I measure. I have also check for any shortage in the mains wiring before the transfomer, but everthing seems ok. Greatly appreciate any feedback.

Link to schematics:
http://www.sm7ths.se/racpac.pdf

Picture of transformer setup:

[0xdeadbeef]

Wow, I thought I would be the only living person who still uses one of them (well, the 10A version). We had them as default supplies at work - they must be like 30 years old or so.
Unfortunately I can't really help you there though. I'm not aware that any of them actually failed. It's just that most people don't use them anymore.
We also had smaller 3ch supplies from Oltronix which more more or less all failed in the last ten years or so. Most of the time the main capacitor died and killed the bridge rectifier on its way to Valhalla.
Not necessarily the same issue with the large 1ch one of course.

[Smith]

Most of these units I have seen had their output transistors blown (can't rember the types, they where 20-40amp versions). These things are beasts, but their really heavy too. Even for my taste, so I haven't really used them.

As said before check the main filtercaps and rectifier bridge. Most PSU's from that age I repaired had bad caps, and rectifiers after the caps fried them. Take care, as I remember correctly the main cap is 60V and has lots of capacity.  Discharge well before repair attempt! This thing will fry your screwdriver or soldering iron.

The smaller  Oltronix Stabpac series had issues with bad transformers. I have had multiple of them on my bench for repair, and a lot of them spilled their guts  (think old burned electronics and burned oil smell). It friggin stinks, people could still smell it after 4 weeks.

[halexa]

Most of these units I have seen had their output transistors blown (can't rember the types, they where 20-40amp versions). These things are beasts, but their really heavy too. Even for my taste, so I haven't really used them.

As said before check the main filtercaps and rectifier bridge. Most PSU's from that age I repaired had bad caps, and rectifiers after the caps fried them. Take care, as I remember correctly the main cap is 60V and has lots of capacity.  Discharge well before repair attempt! This thing will fry your screwdriver or soldering iron.

The smaller  Oltronix Stabpac series had issues with bad transformers. I have had multiple of them on my bench for repair, and a lot of them spilled their guts  (think old burned electronics and burned oil smell). It friggin stinks, people could still smell it after 4 weeks.

Can an issue on the secondary side of the transformer cause the fuse on the primary side to blow? like a bad filetercap or shorted bridge rectifier?

[Smith]

Yes, it's an overload of the power supply. A shortcut on the secondaries is basicly only limited by the power the transformer can deliver. In this case the transformer is overloaded, thus the fuse should blow.

[halexa]

Tahnks for the feedback.
I will start checking the filter caps and diode bridges. I placed an order for an ESR meter think that will come in handy for this (http://www.ebay.com.au/itm/391313810256?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)
Think I also will remove the connection on the secondary side of the transformer and power it up, cause I still think the transfomer might be faulty.
And I also need to fix an bulb current limiter since I'm out of fuses.

[Smith]

Just disconnected the secondary load, and try the transformer. If that works start measuring SCR1, SCR2 and the two diodes (page 26). This is the rectifier bridge.  I suspect one of these last four components.
In some Oltronix PSU's they where mounted in an 'box' in the rear left corner of the PSU.

BTW be sure to discharge all caps before measuring with the ESR meter! I don't think this one does it automaticly. The caps in this PSU are probably big enough to destroy the meter.

[Stigaard]

I have an B32-30R, it also blew the main fuse, in my case this was caused by inrush current as my mains voltage is around 235V and it was set for 220V. Moved to the 240V tap and never had a problem since.

[halexa]

Update:


Transformer is OK!.

One of the diode: D87A is reading faulty -1.4V

D80 and D81 reads 0.45V
SCR1 and SCR2 reads 2.0V
So these seems OK.

[halexa]

Update:


Transformer is OK!.

One of the diode: D87A is reading faulty -1.4V

D80 and D81 reads 0.45V
SCR1 and SCR2 reads 2.0V
So these seems OK.

Update:
D87A was ok when i removed it from circuit it was reading 0.45V.

Realized that SCR1 and SCR2 should not be conducting when there is no current at the gate. So next step will be to remove these from circuit for further testing.
Also tested all the regulator transistors and one of them was not ok.

[halexa]

Latest staus:

Thyrsitors, diodes and filter caps are all ok.

The thing is the unit is fully functional when i put a current limit ligh bulb (45W) on the mains input. What i notice is that when i hit the power switch the light bulb shines bright as if there is a current rush and after a second it dims. I have tested to change the transformer wiring to 240V as mention earlier without result. If i remove the current limiting bulb the main fuse and house fuse (10A) blows at start up.

I'm a bit lost were to go next, but something is drawing to much current.
Please I need advise what to do next .

[halexa]

Update:

I tried to power it up from an  16A outlet since eariler i usedan 10A. Now the house fuse dosent trigg, but CC is active on the unit without a load on the output.
So maybe there is something funny going on in the current sense circuit.

[halexa]

Been a while, but i got the PSU up and running except for the inrush current issue. Were at power ON the PSU will tripp my outlet fuse (10A).

Descided to retro fit the PSU with a relay soft start. I made a curcuit and layout a board with a resistor current limiter and a delayed relay that will by pass the current limiter.

Attached is schematic and PCB.

Will update when i actualy test the retro fit.

[halexa]

Success.

The soft starter works like a treat.  . So no more blown house fuses and the PSU is fully functional again.