Need cap replacementt advice Chang CD288H / HE

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

Glad to hear it is working again and cool repair.
The caps angled like that should also definitely allow more air to pass through the heatsink next to them - which is good. I've personally had to install caps slightly-angled like that before as well due to being too tall and not fitting in the monitor case.

So yeah, it should be okay for another 5-10 years, at least. Don't know about more than 10 years, though. The CCFLs will likely loose their brightness quite a bit by then if used on a daily business basis or 24/7 operation.

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

Well, the United Chemi-con caps arrived 2 weeks ago, and I finally got around to installing them, the TV fired right up and works great.

I wanted to post these images of my repositioning of the capacitors away from the sources of heat to defeat the auto-croak, intentionally roast the capacitors to death design. I used blue RTV silicone (rated to 400° F) on the capacitor leads to avoid any chance of the leads shorting out. I decided not to install a fan, it shouldn't need it.

This TV ran for 2 1/2 years before it started to croak. I suspect that the job security seeking circuit board designers have only put one auto-croak "feature" on the board, and so I suspect that this TV will last 10 or 15 years now before it ever has another problem, unless a bulb goes bad.

Hopefully this will help someone else out in the future. I want to thank all who offered advice and participated in this thread, I really appreciate it.


Parts used are United Chemi-con 1000UF 20% 16V RADIAL and United Chemi-con 220UF 20% 35V RADIAL and United Chemi-con 1000UF 20% 35V RADIAL .

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

Don't think so, that discoloration usually appears at temps above like 120 °C.

It depends on the PCB composition, actually. In my experience, the cheaper FR-2 phenolic boards tend to darken even at temperatures as low as 70C, provided the heat source is present for a long time. With the higher-grade PCBs, it usually takes 80C-90C and a very very long time for the board to darken even a slight bit.

This PSU does appear to use a slightly-higher grade PCB, so that heat under the caps could as well be from the minimum load resistors. If that's the case, you just get a load resistor with the same value and mount it somewhere else further away from the caps.

[Behemot]

Re: Need cap replacementt advice Chang CD288H / HE

Minimum load resistors, burning power.

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

This is an image of an identical board. See the red rectangle. The 4 surface mount devices are all resistors, between and underneath the 2 capacitors, where the board is browned.

[Behemot]

Re: Need cap replacementt advice Chang CD288H / HE

Don't think so, that discoloration usually appears at temps above like 120 °C. Crappy electrolytic caps would blast long ago at that temp. It may be some residue if they've been leaking. Or there is some semiconductor on the solder side?

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

Ah okay.
Seems like you know what you're up against with the fan cleaning and noise. In that case, I'll leave you to it. Just wanted to make sure someone clueless ins't trying this and then complaining the "fix" didn't last.

I hear that. Only a maglev fan should be used, a ball or sleeve bearing in a small fan won't last very long. And it will require cleaning from time to time. I appreciate your input.

Wouldn't at least some part of the board roasting be due to the original failure of the capacitors. Once they start losing capacity and ESR, don't they start heating up more when doing the same work?

No doubt. A good point.

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

Ah okay.
Seems like you know what you're up against with the fan cleaning and noise. In that case, I'll leave you to it. Just wanted to make sure someone clueless ins't trying this and then complaining the "fix" didn't last.

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

That particular fan above is a 5V-rated fan, so it might not be too happy on 12V. Or at the very least, it will be extremely loud and probably won't last long. Possibly even with 5V it might be too loud. Those appear to be laptop fans, so running them all the time is not recommended.

Oops, my bad, I must have gotten distracted. I meant the 5V on the TV power supply.

The noise I don't mind, I'm used to it. I have a 6 inch 12V maglev running at 7.5 volts blowing down warm air from the ceiling and it is still loud... a po' boy ceiling fan, the ceiling is too low here for an actual ceiling fan.

But I've been running it for 7 years now, just have to clean it every so often. I've also been running 2 other maglev laptop fans only slightly larger than those laptop fans for almost as long. You underestimate the longevity of magnetically levitated bearing fans. You just have to clean them once every 2 years or so to get the dust buildup out of the blades and housing.

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

I also found that I have 2 of these tiny maglevs laying around. Pulls only .06A, so I should be able to wire one right into the 12V of the TV power supply and cool off that area of the board.

That particular fan above is a 5V-rated fan, so it might not be too happy on 12V. Or at the very least, it will be extremely loud and probably won't last long. Possibly even with 5V it might be too loud. Those appear to be laptop fans, so running them all the time is not recommended.

[rugger]

Re: Need cap replacementt advice Chang CD288H / HE

Wouldn't at least some part of the board roasting be due to the original failure of the capacitors. Once they start losing capacity and ESR, don't they start heating up more when doing the same work?

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

KYB is 5mm shorter http://www.digikey.com/product-searc...350ELL102MK20S

I appreciate the info, but I already ordered. I found that there is easily enough room to bend them over so they orient horizontally instead of vertically. I also found that I have 2 of these tiny maglevs laying around. Pulls only .06A, so I should be able to wire one right into the 12V of the TV power supply and cool off that area of the board.

[Behemot]

Re: Need cap replacementt advice Chang CD288H / HE

KYB is 5mm shorter http://www.digikey.com/product-searc...350ELL102MK20S

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

I decided to use 1000uF 35V and 220uF 35V and 1000uF 16V. All United Chemi-Con instead of Panasonic.

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

If you have the space, then go for it. I would also advise you run it on 5V, because on 12V it might be very loud (at least most Pentium 3 -era fans are)

Excellent advice. The lower RPMs should keep the dust buildup to a minimum too.

Well, why not just solder the copper bus bars to the thickest areas of the PCB and without putting any caps on them? Then, the copper bus bars will simply serve as a heatsink and nothing else.

This might also be a good idea, but I have to see if there is enough clearance on the solder side of the board. When mounted, there is only a small clearance to the metal back of the display panel.

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

Going with installing a fan is a good idea, I will probably install a Pentium 3 class CPU heatsink fan along the edge of the board.

If you have the space, then go for it. I would also advise you run it on 5V, because on 12V it might be very loud (at least most Pentium 3 -era fans are)

I wonder if running two copper bus bars out past the edge of the board (on top of the board under the caps) and installing 2 more 1000uF 35V caps on this bus, so all four are in parallel, would work to reduce the heat generation? There is enough space to do it, and the copper would also act as a heat sink.

Well, why not just solder the copper bus bars to the thickest areas of the PCB and without putting any caps on them? Then, the copper bus bars will simply serve as a heatsink and nothing else.

I've done something similar with 14 AWG solid wire - just soldered a long piece on the tabs of several TO-252 MOSFETs to act as a heatsink. And it worked well.

[nfadel]

Re: Need cap replacementt advice Chang CD288H / HE

Here is the video I took the image from. A bit higher resolution and you can full screen it.

These are some generic images of the PC220P power supply board in case you recognize it.

Going with installing a fan is a good idea, I will probably install a Pentium 3 class CPU heatsink fan along the edge of the board.

The two 1000uF 35V caps go on top of the browned area, and they are in parallel in the circuit. I wonder if running two copper bus bars out past the edge of the board (on top of the board under the caps) and installing 2 more 1000uF 35V caps on this bus, so all four are in parallel, would work to reduce the heat generation? There is enough space to do it, and the copper would also act as a heat sink.

[stj]

Re: Need cap replacementt advice Chang CD288H / HE

leaky diode cooking the caps maybe.

[Behemot]

Re: Need cap replacementt advice Chang CD288H / HE

In these displays, bad caps are often the cause of overheating (excessive switching). You change the caps, may stick a small passive in there too, and everything is good.

But discoloration directly under caps is strange, what's going on there?

[momaka]

Re: Need cap replacementt advice Chang CD288H / HE

I've never encountered any problems moving them off the board, but I've always avoided routing the wires near inductors.

Sometimes you have to consider the unknown values introduced by heat roasting though, too. A carbonized board eventually equals a short circuit. My current power supply board:

If you have problems with heat, you don't simply move the caps away to keep them from roasting. Instead, a better solution would be to remove as much as the heat as possible. One way to do that in a power supply is to use bigger rectifiers with lower Vf drop... or forget about rectifiers (diodes) altogether, and use a synchronous rectification design with MOSFETs.

Better yet, to keep things simple, just install a low-RPM fan or put more holes in the case to allow for more air to come in and go out. Even a tiny bit of air movement can create a dramatic drop in temperature sometimes.