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Old 05-17-2021, 07:37 PM   #3136
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Default Delta Electronics DPS-300ab-15b REV:01F [PCB: DPS-300ap-15b] - recap & mods

After decommissioning the above DPS-300ab-15b PSU from the Gateway PC that it was in, I put it on the shelf with the intention to recap it. I already knew it had a 2-transistor 5VSB design (with a “critical” cap too), so a recap was undoubtedly going to be required at some point in time. In 2018, however, I ran short on working PSUs while putting together some spare PC builds. So I installed this PSU (still with the original caps) as a “temporary” thing in a HP PC with an Athlon II X2 that I didn’t care much about (due to having some issues with the motherboard.) To say that I didn’t use this PC afterwards would be an understatement. I connected it to power maybe only twice in 2 years. Then, last fall as I was fixing up another similar PC and needed to power up the Athlon II X2 system to try some tests on it with the hardware from the other system, I of course ran into issues with this unrecapped Delta PSU. Basically, as soon as I applied power, I heard a very high-pitched squealing, whining noise. I powered off the PC, but the noise continued. At that point I was almost certain what the issue was – bad caps on the 5VSB, likely. So I unplugged the PSU almost immediately. And I was right about the problem!

Delta DPS-300AB-15B REV-01F - failed 5VSB cap.jpg

After so many years, I suppose those CapXon GL caps beat the Ltec to the finish line (of FAIL.) I swapped out the bulging CapXon GL, 16V, 1500 uF with a Nichicon HN, 16V, 1500 uF that I had on hand. This fixed the 5VSB squealing on the spot. Of course, I put the PSU aside again, so that this time I could finish the recap (as I had planned when I originally decommissioned the PSU.) Besides, the Ltec caps were also starting to show suspiciously increased capacitance, IIRC. So eventually I did the recap and this was the result:

Delta DPS-300AB-15B REV-01F - recapped v1 (1).jpg

Delta DPS-300AB-15B REV-01F - recapped v1 (2).jpg

To understand what is going on, here is a cap diagram of the output capacitors:

As you can see, I still didn’t do a 100% full recap (left the 2nd 5VSB cap and 2nd 12V rail caps with the original Taicon ones, as Taicon doesn’t seem to fail very often in Delta PSUs.) The 1st -12V rail filter cap was replaced with a recycled Taicon (from another Delta??) The 12V rail also received an “interesting” treatment: the Ltec LZG 680 uF cap was replaced with a Rubycon ZL 1200 uF cap and the CapXon GL 1500 uF cap was replaced with an Ltec LZP 2200 uF cap. Both of these were recycled parts (the Ltec I think I pulled from the 12V rail on one of the HiPro 300W units a few pages back.) But apart from these, the rest of the PSU received good caps. The 3.3V rail received 2x new Rubycon ZLH 6.3V, 2200 uF. The 5V received 1x Panasonic FC 16V, 2200 uF, 12.5 mm cap (recycled part from Vcore on a Foxconn motherboard, so best not used on higher voltages) and also a new Rubycon YXJ 10V, 2200 uF part. As for the “critical” cap on the 5VSB circuit, I don’t actually remember what I used as a replacement there or if I replaced it at all. It was a Taicon PW and measured good ESR and capacitance. So I might have left it for when I get more 25V, 100 uF caps, as I don’t have any ATM.

After giving the PSU a recap, there was still one thing I wasn’t too keen about – the discoloration / PCB darkening around diode D951 on the primary side next to the 5VSB transformer. This darkening has been there ever since I took the pictures of this PSU back in 2014. In this case, D951 is the rectifying diode for the primary side auxiliary rail, which provides power to both the 5VSB feedback circuitry on the primary side and also power to the PWM controller on the primary. Like with the DPS-300KP PSU I showed, this diode is just a standard 1N4002 (not 1N4001 as I noted in the 300KP post – that’s a mistake.) I’m not sure why Delta insists on using a regular diode here (not even fast-recovery type!), though when I tried changing it in the Delta 300KP PSU, the 5VSB lost regulation and started oscillating wildly. Of course, I wanted to see if the Delta DPS-300ab-15b would do the same thing, so I tried it again – I replaced diode D951 (originally 1N4002) with an FR153 diode. What’s interesting is that the 300ab-15b did not have any problems with this change and the 5VSB circuit continued to work normally. However, even my new diode there was still running a bit too hot (though not as much as before.) Therefore, I removed it again, soldered a piece of used copper braid to the Cathode lead, and then soldered it back in the circuit. You can actually see that modification in the first recap picture I posted above (on the left side.) After doing this, the diode seemed to run a bit cooler as the copper braid was doing its job of sinking heat away from it.

And speaking of the 5VSB circuit, I drew the schematic of that so I could get a better idea of what’s going on. Here it is:

Delta Electronics, [PCB] DPS-300AP-15b 5VSB circuit schematic.jpg

One interesting note for the DPS-300ab-15b 5VSB circuit is that it looks very similar on the primary side (despite me arranging the components on the schematic in a slightly different order) to that of the HEC Orion HP585D PSU I posted a while back. That said, both of these 5VSB circuits are quite power-hungry and easily waste 3-4 Watts without a load. (Well, that hot diode in the 300ab-15b has to take its power from somewhere. )

Finally, I replaced the STTH1602ct fast recovery rectifier on the 12V rail with an MBR20100CT that came from the KDMPower MIPC MI-X8775CD PSU that I repaired not too long ago. That PSU can’t really provide much power anyways, so it was a bit of waste to have 2x 20 Amp Schottky rectifiers on its 12V rail, while the Delta DPS-300ab-15b was just chugging barely along with a single 16 Amp FR rectifier. You can see the “new” 12V rectifier in the Delta PSU in the 2nd recap picture above. This did actually improve the 12V rail cross-load regulation by about 0.2 to 0.3V and brought it much closer to 12V under load. So I think that was a good change.

And that’s all I really have for this Delta PSU. Now cast your votes when you think I will have to open it again to change that 2200 uF Ltec LZP cap on the 12V rail.
Attached Images
File Type: jpg Delta DPS-300AB-15B REV-01F cap diagram.jpg (219.6 KB, 240 views)

Last edited by momaka; 05-17-2021 at 07:38 PM..
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