Beware STK4278L lot# E422

It was impossible to converge, kinda wish I hadn't tried.

It's not clipping, the DC controls move the raster evenly over the whole screen, nor is there any significant DC offset. I believe the problem is an insufficient slew rate (high frequency response), so some may be better than others. Some may converge but I'd rather have an in spec part.

This happened in a Sony EXR series projection, they and similar Sonys are the only sets I've ever seen these ICs in, if there are others the ICs might work, but I dont see how. It's obvious they're not going to work in these. So don't touch those dials and don't bother troubleshooting the waveform generator.

Last time this happened to me it was nowhere near as severe and with a scant ½" of extra overscan the set looked good. This one would've needed over a full inch, I can't do that.

I thought it worth mentioning because there are alot of these sets around and most have strong CRTs. What's more, I don't think these sets get more than ½ a dozen different problems, H tuning cap/Hout and H regulator, the occasional flyback, diodes in the SMPS/2SC4582. The only really bad thing I've found is those %&*#$ SRS modules and the set is good enough I think to use an external sound system. I've only seen one bad CRT in them ever. When they first came out I thought they were a bitch to work on, but more recent designs have caused be to do an about face.

JURB

Maybe counterfeits? Who are you buying them from?

Mark Z.

They came from a local supplier because we wanted them fast. We have had problems with some of their parts, but not all.

I don't suppose their going to reveal their sources, but if anyone on this NG runs into some E422s that could point the way.

In a way I have trouble understanding counterfeit ICs, somebody goes to all the trouble to make the series of masks, get everything and the process going and has a run of ICs that meet all the JANTX specs except slew rate ? I just don't think this likely, but that doesn't mean it's impossible.

I think it's more likely that the actual manufacturer nade them, found them under spec and sold them for scrap, then the scrapper, using some testing equipment tests them, but can't do it under actual operating conditions, deems the IC good and then sells it.

To have this crappy slew rate or the wierd distortion in these ICs which actually do work I'll bet the substrate is good, and I'll lay money on that they bought or produced some crappy PNP output devices. Whenever I ever saw this happen it was on the left side of the screen. In silicon, PNP devices are harder to produce, I don't remember the reason right now but I think it has to do with the dopants. The opposite was true of germanium devices.

Yes indeed the ouptputs are semi-discreet in these ICs, once you get one that's really stuck to the heatsink and the cover pops off as you hammer it off of there you'll see what I mean.

If I were to make really counterfeit ICs there would be nothing in there. I would sell IC packages without a chip inside, if someone really wanted to make a bunch of money fast why go through all the bullshit. Billy Joe told Bobby Sue to go on take the money and run. Doing this along with the hierachy of distributors etc., one could make a nice piece of change before TSHTF and be gone. The difference is that these things work, almost.

A whole different possibility is that the real manufacturers are deliberately polluting the market. I wouldn't put it past them, not after seeing their products.

JURB

Jurb is right, the STK is easy to break open and everything is potted in clear soft silicone, and the amp dies on crunk of copper cubes covered with either clear silicone or black hard potting.

Not that hard to reverse engineer by probing and taking apart a bunch and seperate hybrid board in pieces to get precise measurements on certain printed on resistor strips.

Same with older switching STR ICs (metal baseplate) like used in Zenith chassis.

Still, I still really think the design of package is very poor thermal-wise. When one bolts down a STK IC (two screws), the IC bows, middle part gets thick layer of silicone heatsink compound plus the plate is aluminum instead of copper. I'm talking about STK 730's, STK

Sigh.

Cheers, Wizard

We used to buy generic STK's from Andrews Electronics. Some of them were so poorly made the legs fell off right there in the parts bag.

The transistors I bought from them were "2SC3182 - 2SA1265" and "2SC3281 -

All were counterfeits in SK bags but with "Toshiba" printed on the parts. Only thing is, Toshiba had discontinued them long ago. When the parts failed under even a light load, we busted them open. The interior finish quality was inferior, and the semiconductor dies were only 2.5mm instead of 5mm which the originals were.

Nowadays we only buy semi's from the original manufacturer or B & D Enterprises, who is a distributor for Sanken, etc and whom we trust.

Mark Z.

Mark D. Zacharias wrote: rd

I had the same problem with semis (power devices) from Tritronics. Pure garbage. I buy most of my semis in the original packages direct from Panasonic, Sony, Toshiba, Hitachi, Mitsubishi, etc. They do cost a lot more, but NOTHING is more expensive than a re-check. When I repair something, I don't ever want to see it again, at least not for the same problem....

I also buy semis from Electronica in Denver. I talked to the owner who swears he buys directly from the OEMs. In three years dealing with them, I haven't had one failure. I heard from others that B&D electronics also has good devices, but I have no experience with them.

John

B & D are great people, and the product is first-rate. I'll keep Electronica in mind.

Mark Z.