PFC Controlled Power Supply Unit Repair
This repair is about those newer and more difficult P.F.C. controlled PS Units. Like the recent very helpful articles from Paris. (Especially the Posts after his recent article were very informative!). I had repaired the simple Power Supply Units with an easier TL494 controller in it before (like a 400 Watt ATX supply that had a bad Cap). But the Power Supply this article is about, took much more time to find the culprit.
The P.F.C. controlled Supply was a HP DPS-300AB-49A 300Watt Desktop Supply. Probably also known under other names like Delta. I couldn’t get it working and I thought I really had checked every component (at least all Semiconductors). One of the ICs was an (F)AN4800 controller with a TNY277 standby power switch. Because I had checked all semiconductors being fine I decided to replace both ICs. But that was no help either. Because after I replaced the AN4800 and TNY277 nothing had changed.
Finding the circuit of this Unit was not possible but I had found a lot of different schematics with a TNY277 in it. However finding a circuit with a (F)AN4800 controller in it (or with a pin compatible CM6800 controller) seemed impossible too. Therefore I decide to draw the circuit myself from the unit at hand.
Above schematic was the result I had drawn. It doesn’t look complete but it was enough for me to find the problem and fix the Unit. And this information now will also help me next time to analyse and find the problem more quickly.
Above Photo shows the inside view of this Unit. On the right the Primary Hot (DANGER! Do not touch!) side with the rectified AC 400-450V on the capacitor below. The Greatz Diode Bridge is in the top right under the Fan with a Cooler attached to it. In the middle between both vertical Alu Cooler Plates there are the 3 Optocouplers, all three Transformers, and the (F)AN4800 plus the TNY277 chips. In the top middle there is the Line filter with 2 four pole Coils and the 3 Line Filter Capacitors.
The Fuse on the left from previous Line Filter was still intact. And also the 450V reservoir Capacitor measured working fine after connecting to the 230VAC Power Line. I could measured the rectified HV DC voltage over its poles.
Next I will show all Photos I took to explain the component tests I had checked. And because I couldn’t find any defective Semiconductor on the Cooler Plates, neither primary nor secondary, I soldered them back into the Board. And as it turned out also this Power Supply was fixed by just replacing a very cheap component that prevented this further undamaged Unit from working.
And with the schematic I made it is easier to see how these Units operate. And why they fail without really being damaged at all! Following Photo shows the inside after removing the primary Cooler Plate with the 4 Semiconductors on it. And the Photo after that shows these Semiconductors.
Above a closer view on at the (F)AN4800 and the TNY277 chip plus the 3 optocouplers on the Primary side after the Primary Semiconductor Cooler Plate was removed.
Above view shows the Primary Cooler Plate with the 4 Semiconductors in Close Up. On the Left 2x 10N60C Mosfets. The Diode on the right of them is not easy to read “Withboard 40STVU CHN 031?” and the semiconductor at the right looks like a GEF 035 plus some also unreadable text. But that didn’t matter because they all checked out fine!
And there was also a vertical placed small Board at the secondary side of this Power Supply, with if I am correct, a LM339 circuit on it. And it is probably just the temperature measuring and speed controlling Board for the Fan. Therefore I didn’t think this Board had any doing in the problem of the Supply. And I had not checked any of the parts of this Board. (See first Photo after this text).
To end this successful repair, here also follow the Photos that explain the cause of the problem why the Unit failed to work. Which was also the weak link in the chain being this PSU circuit.
Another Power Supply Fixed at no cost at all !!
Thanks to the recent 5V standby circuit Tip from Paris from Greece, more of these modern P.F.C. controlled Supplies are likely easily Fixable. Checking the (F)AN4800 or the CM6800 controller Datasheet didn’t help, but checking the TNY277 explained were to look further.
Please click on the schematic to enlarge it
And to give some technical background on this repair I add above schematic with the TNY277 circuit in it.
Good luck with repairing those newer P.F.C. (improved Cos Phi Energy saver) SMP Supplies!
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: