thankyou for the help as its busted im going to replace it any wayCounting from the left, the four pins are: "+", first AC pin, second AC pin, "-" .
The results shown above are measurements across "+" and "-" , in both directions. One of the results, with + ( i.e. Red meter lead ) on "-" and - ( Black meter lead ) on "+" shows 1.13, which is the forward-conduction value across two diodes in series.
The last two tests requested were
1. Red meter lead on "-", black meter lead on the first AC pin from the left.
2. Red meter lead on the second AC pin from the left, black meter lead on "+".
Test 1 has effectively been done, by conducting through two diodes to the "+" pin.
I'm fairly confident that the rectifier is OK, but some other component is shorted and causing the fuse to blow.
@ajlelectronics sorry i missed this bit yes not pure black but there is defo blackness thereIs the fuse black inside? That would tell me that the chopper transistor is short circuit. The bridge rectifier is probably objecting to the short circuit current, so will also need to be replaced. Depending on the age of the board, I would also be swapping out electrolytic capacitors, particularly if any of them look bulged on the top.
The board can be tested to check if there is a shorted component deeper inside the inverter power section without needing to fit a new rectifier first. I would suggest delaying new parts until we know where the original fault is.thankyou for the help as its busted im going to replace it any way
ive tryed to test the board where the bridge rectifier connections sit in to i can only get a reading the far left and the far right and if i swap the leads round i get a higher reading than the first
should i be getting readings from all pins on the board ?
again thanks for your time i was not ordering the rectifier as yetThe board can be tested to check if there is a shorted component deeper inside the inverter power section without needing to fit a new rectifier first. I would suggest delaying new parts until we know where the original fault is.
In the location where the rectifier was, the centre two tracks are the AC input, which will go back to the mains lead. The outer two connections are the DC output from the rectifier to the smoothing capacitors and the inverter power transistors. If there is a short, it should be apparent on the 200 Ohms range, and I would expect it to be the same value both ways. However, you might need to check on the 2K range, and maybe try Diode Test too.
The rectifier's DC output pins are the "outside" ones, i.e. "1" and "4" if you were counting from the left. Pin 1 is marked with a + on the board, and the white printed rectangle has the corner cut diagonally. That is the positive DC output, and the furthest one, pin 4, is the negative.
When a rectifier is normally installed and working, the AC mains goes in on the 2 inside pins, and provides 325v DC across those 2 outside pins, the + and the - . Those tracks are wired directly to the large black smoothing capacitors, which boost the voltage to 325. If the caps were shorted, they would bulge out or explode. From there the 325v DC Bus gets chopped to look like high frequency AC, at 20 to 100 KHz. This is done by the MOSFET or IGBT power transistors, mounted on the aluminium heatsinks. This AC gets stepped-down in the ferrite-cored transformers and then rectified to provide the low DC voltages that the power supply is designed for.
The two outermost pin locations, on the board, may have a short-circuit in one or more of those transistors, and this would be indicated by a low Ohms value on the "200 Ohms" range, or if not, then maybe on the "2K" or the Diode Test range
Thank you for the results. There are no solid short-circuits, but something must be drawing excessive current and blowing the fuse. Maybe rather than being switched on & off 50,000 times per second, one or more of the transistors is being held on, due to a fault in the control logic. That will be harder to diagnose, compared to a simple short.
Instead of AC mains and the rectifier, use a low voltage current-limited DC supply, of about 30 to 40 volts, connected to the + and - tracks where the rectifier was. Then you need to look at the control signals on the gates of the power transistors, using an o. If the current-limit on the bench power supply ( set at perhaps 1 or 2 Amps ) trips immediately, you will have to take each of the transistors out-of-circuit in turn, to allow the control logic to run and be checked out.
The problem area looks like it could be a psu section for the main control system, I suspect it uses something like a Viper-22A 8 leg offline PWM chip, PCB connections seems to match that.
I think the PC tracks from the mains cable go to the rectifier ( maybe via a noise filter ) and no-where else. If the tracks do go to other parts of the board, then it would be worth trying it without the rectifier in the circuit.more for testing items that requite dc drills ,electroics older games systems that i could throw the leads on and dial in power
i dont supose it worth powering it on with the rectfier removed to see if we can see any faults ?
thank you for the heads up on the sales they look what i thought this was going to be older item the rs one looks nice be keeping an eye on thatI think the PC tracks from the mains cable go to the rectifier ( maybe via a noise filter ) and no-where else. If the tracks do go to other parts of the board, then it would be worth trying it without the rectifier in the circuit.
I think what you need is a bench power supply, e.g.:
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The case is a little rusty, with a few scratches.www.ebay.co.uk
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