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Need help repair Sunshine ATX psu

73's de Edd

Aug 21, 2015
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Aug 21, 2015
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Sir mikey5791 . . . .


EVERY semiconductor which you tested seems to be having a good reading to me.
On reading the frontal side of the power supply, near the first heatsink I am seeing three POWER semiconductors.
The second one over from the far right is labeled as Q4, they are the MAIN power transistors for the main power supply of the unit.
There is one sole transistor mounted at 90 degree angle at the left corner with a plug on female connector which connects over to your stand by power supplies circuitry , that power transistor, drives its companion power transformer as the EEL – 19T3 unit.
That leaves the ATX – 1AT as being the driver transformer for the main power supply with the largest ATX 33 T1 as being the units main power transformer .

I can see the socket for your circuit protective " lite bub " sitting over to the left and the manner in which it has responded for you, is just exactly as should be expected, with its initial slight glow up, and decline, at the initial onset of the charging up of the two large capacitance, main raw DC power supply electrolytic capacitors .
You still do need to implement a junction test on the two main power transistors that I had earlier mentioned, with my suspecting them to also be good, as was your C5027 transistor of the standby power supply.
With all of the major power supply MAIN semi units intact . . . If the two main power transistors still to be tested are okay . . . as well as the initial full wave bridge having been good and no "HARD" blown line fuse having been found in the unit.
It just seems like the unit may have NOT experienced a " HARD " failure of a major component, but instead, just a gradual decline of the unit to an inoperative " SOFT " failure state, this probably being attributable to an increased ESR value of one or several electrolytic capacitors in the unit or the other possibility of a failure of the K7500 SMPS driver I.C.of the unit .
To test it in circuit, duplicate the past hook up of the unit to the same conditions where you were expecting the unit to be working.
I remember you as having no silly scope , so let's give you a viable workaround via DVM in its A.C. input mode.
Meter BLACK negative lead will be going to the same ground connection as pin 7 of the 7500..
Meter RED lead will go to a 0.1 ufd for D.C. isolation, since SOME DVM's go bonkers in their readings with a combined AC/DC voltage presence.
Now go to your awaiting power supply test bed and monitor through that cap, to I.C. pins 8 and 11, to confirm if there is being any drive output from the I.C.
If none is there power down and wait for power supply capacitor voltage decline, or shunt them out and then inspect the data sheet schematic of the internal circuitry of a 7500 .
There, you will find that they are using two totem pole bipolar transistors at the output stages .
Their collectors -emitters are being between pins 8-9 and 10-11. Take your DVM go to the diode test mode and check with both test lead polarity possibilities of there being a short in the junctions of one or both transistors .
Also try testing in the low Ohm's mode.

73's de Edd
 
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