Quote:
Originally Posted by
norm1968 
I'm a recent new owner of one these boxes, the Hisense HDTV tuner, and it looks to me by the trend of quite a few posts here that the Hisense box suffers from the "Bad Caps" plague. Read about what I'm talking about on Wikipedia, the article titled: Capacitor plague.
On that Wikipedia page they also have a picture showing what a typical internal "power supply" looks like. Power supplies can be external boxes on the power cord outside the box (typical of laptop PCs) or they can be on printed circuit boards inside, as the Hisense box has.
My PC purchased in 2003 had bad caps, and I replaced them all myself successfully and got the mother board (and PC) to work again. I might suggest there are web sites (some are mentioned in the Wikipedia article) that will sell you a set of replacement caps relatively cheap. As I recall, I purchaed about 8 for my PC resurrection project for about $12.
My advice would be when replacing caps, use the same capacitance value and voltage as the originals. Although there's nothing wrong with going to a higher voltage, they would be more expensive, and it's probably not necessary. It's very unlikely the originals failed due to improper specs, and more likely they were defective due to the "Capacitor Plague".
-Norm
There may have been an extra bad batch, but my years of experience say it is more than that. I worked TV in late 70's. This was the period of transition to mostly solid state, but occaisonally I'd see one of those early 50's round picture tube sets. Going back to that time frame, you might say every component on them was discrete. Tons of parts. And power was derived from a transformer that weighed maybe thirty pounds and had multiple windings for each required voltage. The beauty of the transformer was that it made the system very tolerant of surges, spikes, and lightening strikes, as long as it was not a direct strike. The reason for these old sets still existing, mostly RCA, was they built them like a Gulfstream, more than they had to be to meet minimums.
Through time most manufacturers have adopted a close to minimum approach to hold cost down and maybe a bit of GE philosophy, the father of planned obsolescence.
And as we moved into the solid state and integrated circuits, there were many design weaknesses. One of the major ones was they did not design in a way to overcome the replacement of the costly power transformer. Silicon just can not take those huge spikes that transformers and vacuum tubes could then. Today we have surge suppressors to help.
But capacitors, they have cut them to the minimum because of cost. You have not lived until you have your face inside a set and one of those electrolytics explodes. A medium sized one sounds like a shotgun. And that can is filled with foil that can spread confetti into your face.
An example of how close they are cutting the tolerance, look at the caps on the board of this unit. You will find two caps of equal value but one is rated 16V and the other is 10V. It would be my guess they came down the same assembly line but when tested at the end, the 10V was weaker than the 16 for the voltage test. They both would have been within capacitance spec, so they sold the 10V at a slightly lower price, maybe $15 per 100. Design engineers pick from ready made components when possible because they are cheaper than special order and if they have orders to pick price or end quality, they go with the cheaper part when possible. We, having to buy retail, will likely pay a bit more than the 15 cent difference, maybe 60 cent. So I ask, for a bit more money, do you want that extra margin of reliability the company did not put in?
It is likely you will not see a significant increase in price for any of the capacitors on this board by doubling the voltage spec, unless it ends up being an un-common value.
If we were looking at say a 4700MF at 1000V and chose to go to a 1600V, then I'd expect to pay a few more dollars. I think the biggest cap I saw was 68MF at 450V. 68MF, not the voltage, sounds uncommon to me and you might pay a bit more for it. Unless you happen to find one of those bag of parts for a few dollars. They quite often have a few common capacitors and then some of those un-common ones because of overstock.
I hesitate to say it would be OK to increase the capacitance to a more common cap of 100MF without knowing the circuitry it is used in, but do not hesitate to increase voltage, especially at the front of the board circuit-wise. That is where power is fed in and you are susceptable to anything on the line.
BTW, lightening suppressors, surge suppressors, and UPS are not 100%. All have a reaction time before clamping and in those few nano seconds it may be too late. Isolation transformers are stil one of the best means of protection, but costly.
