Can you identify a replacement Zener Diode

[kaplang]

The Zener Diode is from a Sansui Eight Driver board Sansui part # 0310830. I need a replacement but I don't know the value. Any help would be appreciated.

 

[33&athird]

Are you sure that's a zener? the schematic diagram on the unit is a standard diode, not a Zener symbol...

I wish I could help more, but I gotta point out, that's one weird lookin' diode:yes:...out of curiousity, what warranted a replacement?, I haven't heard much about diodes failing, but I assume something went wrong:scratch2:

 

[kaplang]

The service manual calls it a Zener. It tests as open both directions.

 

[ecluser]

ZB1 crosses to a ECG5079A, a 20V, 1W zener diode, in my vintage ECG master replacement guide. I didn't downloaded the schematic to see if it makes sense.

 

[kaplang]

Thanks ecluser

If you had the data sheet for an ECG5079A. How would you determine if it makes sense? How can you know the value of the ZB1?

 

[33&athird]

The service manual calls it a Zener. It tests as open both directions.

well, yeah...uh, "Theres your problem"

Glad to see someone has information in getting a new one, As i'm not familar with zeners much, and Sansui even less so. One funky diode, neat looking though, I may have seen one like it a while back. I can only assume that modern replacements will probably look more standard.

 

[EchoWars]

A 20V zener does not make sense. The zener sets up a stable voltage when is then tapped with a trimpot to set the current in the input differential pair. According to the scat, the voltage at the tap is only 2.04V. A 20V zener would make this a damn touchy adjustment, unless I'm looking at this from the wrong angle.

Seems the part number (ZB-1-8) may be providing a clue. I'd suggest that it may be an 8V 500mW zener. The supplied voltage at the B3 bubble is a regulated 46.5V. If the zener was 8V, then the max current in the zener is about 4mA, so a 1/2W zener would be fine.

If one side is functional, it would be a great help to power it up and simply measure the voltage on the cathode of the zener. Mystery solved.

 

[ecluser]

If VR802 is a 3 kOhms pot, R 810 a 10 kOhms resistor and there is 46.5 V at point 8P, it doesn't make sense to put a 20 V zener at ZD801. The maximum voltage between VR802 and R810 would be 10.7V in the absence of the zener. If you measure a voltage lower than 20 V without zener, there is no justification to put a 20 V zener there, and a 8.2V would be more appropriate.

By the way, ZB-1-8 crosses to a ECG5072A, a 8.2V, 1W zener

But if VR802 is a 30 kOhms pot, it does make sense to use a 20V zener.

From this schematic, I am more inclined to think it is a 8.2V zener.

 

[EchoWars]

1W? Seems like the zener would be operating on a pretty soggy part of the knee. But then, it's a Sansui.

 

[ecluser]

If we consider the voltage divider VR802 and R810, the current in the zener is only 1.1mA, so a 1/2 W zener is more than enough for this application.

 

[kaplang]

A voltage reading on the cathode of the good driver board shows 7.5 v :scratch2:

 

[ecluser]

It is within 10% of the nominal voltage of a 8.2V zener. Considering the very low current in the diode, it is not abnormal to have this low voltage.