Sony STR DE-425 centre channel malfunction

I would be looking for a bad trace, or bad solder connections on the board. It is a lesser of a chance that the output IC is bad. Pressing on the board to make the unit work is an indication more of bad solders more so, than bad components!

It is possible however, to have a part that is mechanicaly defective inside, and when pressing on it, makes it work temporarily. This type of event is very rare, and is less than 1% of the time.

As for the output IC, I have not bought these for a while, but I would think it may still be available from Sony. It is advisable with Sony products to use origional parts only, if you want to have long term reliablity from them. When doing service work, I make it a habbit to use origional parts to avoid having returns on my work.

Jerry G. ======

Does it also work if you press on it with something insulated like a screwdriver handle? If so, it's probably a cracked solder connection. Check carefully around hot spots on the board for bad soldering. If it's the conductivity of your skin that's fixing it, I would look for an open resistor in the area you're touching.

Andy Cuffe

snipped-for-privacy@psu.edu

The STK350-230 is a driver IC, not an output. They are available from Sony and from generic suppliers like MCM.

Mark Z.

I was actually looking for bad soldering when touching the board. I noticed that sometimes you cannot see it (before I start touching it I use a bright light and a magnifying glass to visually check all connection in that area) the solder crack is so thin that only by moving the terminals you'll get a result. So when I noticed the change I thought that I found it but very soon I got disappointed: I don't need to apply any pressure (ok... let's say "significant" because if there's no pressure at all there's no contact) to make it work. I tend to believe that is more the skin resistance "short-circuiting" something than bad soldering. More precisely: if I connect the voltmeter (digital) on the 200V scale between the negative pin of C553 and (any end of) JW118 it measures 46V, the speaker's cone goes a few millimeters up (DC voltage on the speaker goes from 0.05 to 2.5V)) but the amplifier works properly. This doesn't look good to me, the amplifier should work well with zero DC voltage across the speaker. I replaced the capacitor (100uF/10V) and there's no change. This capacitor connects pin# 2 of the IC to the "+". I measured the voltages around Q553 and Q445 and everything looks balanced (when I don't have the voltmeter connected as mentioned above, when I connect it the voltage goes unbalanced on the two transistors). I couldn't find any open resistor in that area.. as much as I could verify, without the schematic I'm like a blind man walking down the street with a white stick in my hand. After a couple more tests I noticed that if I use a different voltmeter (a more expensive one) the amplifier works just a little better, not as well as with the cheap voltmeter.... First conclusion: Sony likes cheap staff. I'm inclined to think that the IC has some internal problem and must be replaced. What do you think?

...sm

"Andy Cuffe" wrote in message news: snipped-for-privacy@4ax.com...

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At least try resoldering the driver IC's. This is a pretty common problem.

I went to look at the PDF service manual, but it doesn't include the schematic. Bummer.

Mark Z.

Already did. And not only the driver but other things I thought may be wrong around it. Nothing changed. Then I decided... don't tell anyone! - I connected a 1Mohm resistor between that capacitor and the link, the thing works fine now. For how long it'll work... I wouldn't do this for a client but this is my own thing I'm talking about so what the heck. Not prepared to buy a new one yet. Also noticed that the driver for front channels is operating red hot, installed a little heatsink on it. Thanks guys for all your help!

...sm