help with racal dana  power supply 9242d - Page 1
Forum section: electronics / projects

author: mj21
author_rank: Regular Contributor
timestamp: August 13, 2013, 10:24:43 pm
content: i got a racal dana programmable power supply 9242d at boot sale, its a dual output power supply. now at first the PS worked fine and both channels worked perfectly.but few days ago as i was doing some prototyping and the output of the power supply was off, it suddenly came up with error E2 and now it does not work. i searched the net for a week now and i found nothing on this power supply. channel 2 works OK and out puts ok but channel one gives few hundreds of Milli-voltes with out setting anything then cuts off and displays E2 and this cuts off channel 2 as well.does anyone have any clue of what it can be?

author: Paul Price
author_rank: Super Contributor
timestamp: August 14, 2013, 01:07:07 am
content: Turn off.Looks like there might be some socketed IC's. Try taking them out and looking at the contacts and re-insert.Unplug and inspect the contacts of all these connectors, some oxidation over many years or at high current s can develop bad contacts.Next turn it on and:Sockets and connectors are particularly prone to problems..wiggle the wires, tighten the screws if they are loose.I also see some white screw-tightening type of terminal strip connectors connecting to the large toroidial transformers.Bang around the PCB and connectors softly with a screwdriver handle, wiggle wires around. This might reveal a connector failure or a cold solder joint.Next thing to try is use freeze spray and then a hair dryer over large then smaller areas (is you can create an intermittent fix or fail of components on the PCB. Try this to see if you can thermally locate a thermally sensitive part failing.

author: mj21
author_rank: Regular Contributor
timestamp: August 14, 2013, 08:39:58 am
content: thanks for your response, i have tried everything but no joy. i started to check the voltages at the regulators. the +15 is ok but the -15 was only giving out about -11 so i thought that not right. i changed the regulator but after powering it up one of the caps and the fuse blow up. i changed them and now the voltage at the out put reads 14.87vnow as before the repair the output was reading few hundreds of Milli volts now the output reads 15.47vi checked all the caps for bad ones with esr meter but the rest are all ok.there are two board as you can see in the picture, the first one to the left it the channel two and the one to the right is channel one. they are both identical and use the same parts. but the channel one board also got the bridge rectifiers and the regulators.can the problem be with zenner diodes in the second board? also is there a way i can check mosfets with voltmeter? it might be that output mosfets are damaged

author: Paul Price
author_rank: Super Contributor
timestamp: August 14, 2013, 12:38:57 pm
content: changing the regulator was probably completed with errors and should never result in exploding capacitors.The first new regulator must have been the wrong device or inserted backwards. In any case the abnormal voltage polarity or magnitude result that caused the capacitors to explode may have made things worse and perhaps resulted in other damaging other components. Have you replaced a positive voltage regulator with a negative regulator (or v. versa?)It is easy to check a MOSFET. If you are looking at a MOSFET with the metalized backside away from view, the left terminal is the gate, the center terminal is the drain and the source on the right.Out of circuit, the resistance from gate to d or s should be infinite.The resistance from source to drain should be in the meg ohms with the device removed from the circuit.There is an internal diode from drain to source and will show low ohms like any power diode.Most MOSFETs short out gate to source and source to drain.With most multimeters having a diode-test ohmmeter range setting, applying the positive ohmeter probe to the gate while holding the negative probe on the source should turn on a N-Chan MOSFET and you should see a very lowresistance from drain to source if you then quickly move the positive probe to the drain, keeping the negative ohmmeter probe on the source.You then reverse the ohmmeter leads and apply the negative probe lead to the gate and the positive probe lead to the source. Now the N-MOSFET will certainly be completely turned off. If you then quickly connect the positive ohmmeter to the source and negative to the drain, you should see an open circuit resistance measurement.For P-Chan MOSFETs, all the polarity references are reversed, of course.l

author: mj21
author_rank: Regular Contributor
timestamp: August 14, 2013, 09:53:35 pm
content: no the regulator was soldered in the right direction, i triple checked and beside it is giving the right voltage. the +15 is giving 15.25 so that's with in spec.i am gonna check the mosfets. the most annoying thing with the PS is the PCB, it is so hard to get the parts out with out damaging the PCB tracks. worse case scenario is for me to figure out the pins on the PCB of the channel one and try different PS to work with it. i mean it must have a DAC to set the voltage and current from the MCU, i can make the power supply dave is working on, with out the MCU and the rest of the clutter and just have the power supply bit. as that got the points for setting voltage and current.no wonder racal dana was liquidated and bought by another company, their design is really rubbish. i can see no thoughts of after service and repair was giving when this was being designed. the power components are all cramped together and the topology is all screwed up.

author: Paul Price
author_rank: Super Contributor
timestamp: August 14, 2013, 10:45:21 pm
content: You can check the MOSFETs as I suggested, for shorts, even while they are soldered in circuit. Same is true for zener diodes and other transistors.