On Mon, 24 Sep 2012 10:43:12 -0000, "tjeenz" <tjeenz@...> wrote:
I removed u460. (ca3102 from rca). it is broken (20ohm between 1 and 14 in both directions)
also i found a diode connected on the top to pin 12. i couldn't detect pin 12 in the schematics... now start looking for a ca3102
On Mon, 24 Sep 2012 08:50:17 -0000, "tjeenz" <tjeenz@...> wrote:
Voltage U460 pin3 and 9 is -8.6V, R456 is ok.
pin 1 and 8 are 3.5V not 2.2
That fits with pin 1 being 3.5 volts instead of 2.2 volts. The low
resistance between the collector and base is pulling that node up via
the high output of U480C.
Pin 2 and pin 10 at about 0.0 volts while pin 3 is -8.6 volts suggests
that the emitters of U460E and U460B is open as well.
Pin 12 and pin 5 are connected internally to the substrate. The
CA3102 is built on a junction isolated process so the substrate
connects to each transistor via a diode which is reverse biased to
provide isolation.
u460 is unfortunately not on a socket.
When replacing U460, I would cut the collet pins out of an IC socket
and individually install them into the PC board to make a low profile
socket for the new IC.
To access u460 and area, i see i have to remove some components. I will start on that a.s.a.p. but a question: some loose contact in the timebase switch. sometimes it generates only half screen image when i move with that knob. is that the pot-meter in the middle?
From what I remember of the 2213, the timebase switch uses a different
and unreliable design from the other 22xx series oscilloscopes.
Someone else may have suggestions for repairing it.
David Hess