On Nov 10, 3:20*pm, Franc Zabkar wrote:
On Mon, 10 Nov 2008 09:01:26 -0800 (PST),
" put
finger to keyboard and composed:
This set came in from a local school, dead. As with many others of
these I've repaired over the years I found cracked solder on almost
all of the terminals of the STK 730-020. In the past I've found that
many times simply soldering it up fixes the set. If that doesn't work
then usually replacing the STK does it. I tried soldering first and
the set would still not power up. It did click though when the power
cord *was plugged in. This seemed strange. It does not click when the
power button is pressed though. I looked for obvious things first and
then removed the STK. I have no schematic of the set but I did have 3
new STK's. I compared resistance readings between several pins on the
removed chip with my new one and noted some significant differences.
This suggested that the STK was bad so I replaced it. The new STK did
the same thing so I removed it and compared it to a second new one. My
fist new one seems to now have a discrepancy when compared to a second
unused part, suggesting that it is now very likely damaged as well. I
don't want to chance burning up any more STk's, (if thats what I've
done), *I only have one left. Does anyone have any tips on this set? A
schematic would also be really helpful too if someone has one. Thanks
very much. Lenny.
The datasheet for the STK730-020 ...
http://www.datasheetarchive.com/pdf-...ts-29/DSA-5774...
... has a simple application circuit. Perhaps that will help.
IME with similar designs, common problems are the capacitor between
pins 1 and 3, the startup resistor at pin 4, and maybe the zener
diode. Also make sure the back-EMF diode for the internal MOSFET has
not gone O/C. It may help to know which pins are showing a
discrepancy.
Have you replaced the line stage with a dummy load?
- Franc Zabkar
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Thanks for the link Frank. I'll check those things. Lenny.