Re: New member and owner of a dead 2225


phillip.lyne.barrett
 

Thanks, David, Tom, Tom and Glen.

I've seen those videos. Dave's tear down is really good though my wife makes me wear headphones for any of his videos - she's a non-fan. I kind of get her point...

After following the circuits on the schematic, I think the 38V/67.5V feeds are probably OK because there doesn't seem to be anything particularly sensitive there. Two 100n 50V ceramics are worth looking at, one on the X-Axis Amp and one in the vertical output amp. Everything else feeds though resistors. Though the lowest is 330 so bears looking at a bit more.


It looks like Q912 is not blown, at least a resistance check across the collector and base sees a cap charging up - probably C909 though the 2.2K resistor on the base. Not sure how to determine if either TL594 is dead. I've got the datasheet but haven't looked yet. Will probably order a few just in case, they're cheap.


On the caps, I've found what look like decent replacements - reasonably low ESR, same or better tolerance and all are 105C. However, not a single lead pitch matches. I can make them fit by bending the leads in an L to make them fit the original pitch. I assume that there is no issue with that. So, not worried except for C900 - the big 2200 uF 80V on the mains input board. The only matches are snap-in caps with fat, stiff, stubby leads and the wrong terminal pitch. (10mm vs a measured 12mm on the one that's there now). I guess I can make a little adapter but it will be a bit ugly. If I was industrious, I'd 3D print a foot for it to keep it from moving around - though it will probably be hot glued instead.


Another question. There are at least 9 10 uF axial electrolytics in various places. I should replace them as well? I'm not wild about removing the attenuator/timebase board, though it's probably easier than it looks.


Once I get my ESR meter (due this Friday), I'll hopefully find a smoking gun.


Anyway, again, thanks for all the help. I really do appreciate all your efforts.


Phil

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