C-70: mistake around zeners near T211/T212 ?

[david winter]

Hello,

I am repairing a nice C-70 pre.
Between T211 ant T212 (symetrical sub-power), are two 27V zener diodes (D126 / D127).
The glue used to stick the two 220/35 capacitors corroded both zeners and one had a broken leg. No reference is visible on them, so I took the schematic and realized that it shows a ground connection between both zeners (which is obvious to me) yet the common point between both diodes is NOT grounded on my circuit board.
Which is wrong ? How could the later have not altered the operation ? Thanks.

 

[avionic]

The junction between the two is not grounded like the schematic shows. Two series wired 27 v zeners from the base of TR211 to the base of TR212 .

 

[egellings]

They look like emitter follower buffered zeners. That'll go.

 

[david winter]

avionic: thanks ! I wasn't sure but somehow thought that the mistake had more chances to be on the schematic than the pcb itself.
Will continue restoring this pre later. Just scored a nice Kenwood KA-7100 to do.

 

[Skywatcher]

Hello,

I am repairing a nice C-70 pre.
Between T211 ant T212 (symetrical sub-power), are two 27V zener diodes (D126 / D127).
The glue used to stick the two 220/35 capacitors corroded both zeners and one had a broken leg. No reference is visible on them, so I took the schematic and realized that it shows a ground connection between both zeners (which is obvious to me) yet the common point between both diodes is NOT grounded on my circuit board.
Which is wrong ? How could the later have not altered the operation ? Thanks.

A general rule is, if it worked that way since new, what is on the board is correct.
And the original schematics never match and reflect any in-production changes. They can't change what has already been printed.

 

[avionic]

Tons of mistakes in the publish documents.