Sony HCD DZ280 PSU

[michel74]

Hello everyone,

I'm having an issue with PSU;
When I had it in hands the resistor fuse FR929 (1Ohm) was dead. IC921 (MR4020 - Switching reg.) was dead too.
I replaced both; when plugging the AC cord, nothing goes wrong. When switching On the equipment, the display shows something for few sec, and FR 929 blows again. Not sure if IC921 was still ok, so I replaced both again (...)

Now, when I plug the AC cord, ... FR929 blows directly.

When I measure resistance between pin 3 and 7 (Gnd and Vin) of IC921 I have less than 1 Ohm ... So, I changed it again (IC921) but still this low resistance

Both D921 and C921 are Ok

I'm a bit (completely ?) lost.
Thx in advance

[momaka]

Re: Sony HCD DZ280 PSU

Check C924 and D946 for short-circuit and R916 for open-circuit or higher than normal resistance. Probably best to remove D946 from the circuit to get accurate readings. Also check R922 (0.18 Ohms) for open-circuit.
lastly, if you have an ESR + capacitance meter, check the small electrolytic cap C912 or just plain-replace it... though this being a Sony PSU, I imagine it's a Rubycon, Nichicon, United Chemicon, or some other OK Japanese brand and may not be bad. But nevertheless, this is the "startup" cap and can sometimes cause a lot of issues.
C926 should be checked as well. Also Zener Diodes ZD901, ZD902, & ZD904 for short-circuit, along with D902. Q922 too, if you can.

To prevent further blow up of FR929 and the IC while testing, build yourself a "dim bulb tester" with an incandescent bulb. Details here:
https://www.badcaps.net/forum/showpo...4&postcount=70

^ Start with 40W bulb, but go up to 60-100 Watts if PSU "hickups" (we will get to that part later only if it happens.) I know incandescent bulbs are not sold in the EU anymore, but you can still find 40W ones for appliance / baking oven... and in such case, with lack of higher power bulbs, 2x 40W bulbs in parallel will get you the equivalent of an 80W bulb.

Anyways, check the components above and let us know what you find.

[michel74]

Re: Sony HCD DZ280 PSU

Thanks momaka, so I went around looking for some bulbs and ... hard to find. I will to the test tonight
...
Most of the tests you ask to performed above were already done, but I re-checked the component.
C912 was showing 40uF instead of 47uF, but I replaced it for the other tests, everything is ok.

I wanted to make some continuity check around IC921, but because of the very low value of R922 (0.18Ohm) the tester always bips between pins 3 and 5; and between pins 7(Vin) and 9 (Drain), I have a very low resistance (0.5 ohms) <= I don't know if its normal ...
Thx

[michel74]

A short update ...

After having burn some other fuse resistors and other power IC module, I finally managed to "build" (assemble ?) this "dim bulb tester" as suggested by momaka.. and it definitely helped !
After replacing the fuse and the IC (I think I burned 6 of then ...), when the PSU was powered on, I had no specific issue; but when plugging the main board to it, the bulb was ... blinking. This was a good sign to say that a cap was going mad somewhere;
When I was testing the DC value at the main cap, I was having the 320 Volts ! So I never thought about testing it while PSU was connected to the main board; when I tested it, I only had ... 218 Volts. I had a quick look in the old PSU I was keeping for parts, removed the 330uF/400V cap, tested it (it measured ... 1 to 50 uF varying) so I replace it and ... it worked !
This main cap was the issue, and I never thought it was, because when looking at it ... it looked perfect. No damage, no domed, or swollen top.

Well, just a simple message to say that, without this bulb, I wouldn't have found it before ... month (well, before getting to the point that the last component to change is this nice looking cap)

Thanks again

[sam_sam_sam]

I use an incandescent light bulb when I have switching power supply that is having issues or I do not know what the history of it is
Yes an incandescent light bulb is definitely your friend for troubleshooting a lot of things that are blowing fuses or tripping breakers and if an incandescent light bulb does not have the wattage you need you can even use a heater element instead I personally have not done this yet but I am going to build a jig for one out of toaster oven I just have not needed one so far but if I had one built I would be using right now because I repairing quite a few switching power supply that I have a post about on this forum

One note just because a capacitor is not swollen or leaking dose not mean that it good it might have a very high ESR reading I am a little different than members on this forum when I test a capacitor with a ESR meter and it's reading is close to double what a new one reads I just replace it especially if it is lower than 100uf but that is just me partly because I have the lower UF capacitors in my part bin anyway and generally they are not that expensive when you buy 100 of them at a time up to 47uf any higher value than that I will only buy 10 or 20 of them at a time depending on how much they are and how many you have to buy for a price break on each one

One other note if you are going to repair switching power supply you really should consider buying a ESR meter for troubleshooting them