Zener diodes on 475?


Simon
 

I have found, a couple of short circuited zoner diodes on my 475. They are gold plated and fit into sockets on the triggrer Z axis board, both anodes to ground. They are marked GE 0386, but I don’t know their value. I am wondering if they might be tunnel diodes, although they are marked zeners on the board but I cannot find them on the 475 or 475A schematics. Does anyone have any idea what they might be?
SImon.


Mlynch001
 

Simon,

Those are indeed Tunnel diodes for the trigger circuit.

--
Michael Lynch
Dardanelle, AR


Simon
 

I have discovered that they are tunnel diodes (152-0386-00) and cannot be tested with a multimeter. I am wondering where I can find a circuit diagram that marks them. There are also many discrepancies between my board and the 475 or 475A schematics I have. Maybe there were modifications.
Simon


Simon
 

The trigger circuit seems to be working properly. My problem si a lack of Z axis signal to turn on and off the trace.in sync with the time base.The time base is running and I have X deflection, but no trace as the DC restore circuit cannot function without a Z axis signal.
Simon


Dave Voorhis
 

Per the usual online service manual for the 475, the four tunnel diodes are designated CR556, CR566, CR776 and CR786.

The first two appear on the A8 Trigger Generator and Sweep Logic circuit board (fig 7-12) at locations 7C & 7D.
The second two appear on the A8 Trigger Generator and Sweep Logic circuit board (fig 7-13) at location 7B.

CR556, arming TD, is on the 'A' Trigger Generator schematic 5, to the middle right.
CR566, firing TD, is on the 'A' Trigger Generator schematic 5, to the lower right.

CR776, arming TD, is on the 'B' Trigger Generator schematic 6, to the middle right.
CR786, firing TD, is on the 'B' Trigger Generator schematic 6, to the lower right.

I have found discrepancies between the schematics and my 475 too. For example, the schematic shows the intensity control as a single-gang pot. Mine is a dual-gang pot. The front gang has the part number and circuit matching the schematic. The rear gang is part of the HV regulator circuit, which doesn’t match the schematic.

On 12 Sep 2021, at 17:32, Simon <tenareze32@gmail.com> wrote:

I have discovered that they are tunnel diodes (152-0386-00) and cannot be tested with a multimeter. I am wondering where I can find a circuit diagram that marks them. There are also many discrepancies between my board and the 475 or 475A schematics I have. Maybe there were modifications.
Simon