Download TS850 power problem

Temporary loss of power at the TS 850
The Kenwood TS 850 which we use to drive the 432MHz transverter suddenly lost,
after many years of reliable function, during the July- contest the power- output at the
“Transverter- output” jack.
Here a short description how I was able to solve this problem.
Looking at the diagram, and making some measurements I recognized extremly
voltage fluktuations at the testpoint Nr 3 on the large RF- Board.
Abbildung 1: testpoint 3 at the RF- Board
Checking the power- output with the spectrum- analyser I discovered the same
rhythm like the voltage fluktuations at testpoint 3.
Spending some time to study the diagram and to search for the fault at last I
recognized that the Multivibrator at the DC- DC (X59-100-00) board interrupted his
function from time to time.
After desoldering the coupling capacitor for the Delon voltage doubler at pin 5 and 4
from the PCB I checked the function from the generator again with an oscilloskope.
At pin 5 from the DC-DC board I got a correct signal without any abnormalities.
Connecting the voltage- doubler with C625 to pin 5 suddenly the problems started.
Loading the output- pin Nr. 1 with a 1KOhm resistor aggravated the problem.
The next step was to desolder both diodes which are together in a common case, at
the left picture marked with C3.
As I had not such a device in my stock, I replaced it by two 1N4148 Diodes which I
soldered directly at pin 6,4,2 on the main board (left picture)
After this I got -6V constant level at the pin1 from the DC- DC- board.
The correct level at testpoint 3 from the RF- board is -2,2V in receiving and +2,7V in
transmit- mode.
The right picture shows the 28MHz signal at the transverter- port.
Observing the level for a long time, I could not recognize any changement.
It is not easy to find the DC-DC- board.
If You open the cover from the TS 850, you will find it hidden under the cables at the
right end from this picture.
If anyone has similar problems, I think it could be a good idea to check this
possibillity at the first time.
Michael, DB6NT reported me that one from his TS 850s also had such problems
some time ago, for solving the problem he changed all semiconductors from the DCDC board!
73s
DL6NAA