Dear all,

I have spent several hours (nights) studying the existing posts about miscellaneous display problems regarding the Penta. Yet none has provided the solution. I have a pair of Beolab Penta MkII's, acquired from their first owner (superb overall condition!) One of the displays is working, although fairly dim, the other one is out. So far I have tried the following to fix the problem

- Cables: Powerlink MkII, all pins connected and checked ok

- Also tried to connect the cables vice versa and into different sockets and sources

- Audio/video switch set properly

- Dismantled the display units out of their sockets and swapped them vice versa (both units function properly in one speaker)

- Dismantled the amplifier and checked the Powerlink (Datalink) connection between amplifier and speaker

Still no luck. Does anyone have anymore ideas to get the display fixed?

Kind Regards!

Good straightforward troubleshooting there. The only test remaining would be to swap the amplifiers between speakers, but that may be a lot of unnecessary work...

Unfortunately we only have Mk.I schematics on site, so I won't go too far into details as they might not apply to Mk.II - but from your tests, it seems your other speaker isn't delivering power to the display. It is just about the only thing the displays have to do with the amp, other connections go pretty much straight through it to the Powerlink and Speakerlink sockets.

In Mk.I, there would be 10VAC between pins 2 and 3 in the connector behind the display window. This comes straight from a dedicated winding on the standby transformer (not even a fuse in between) so the most likely problem would be a bad connection. Probably inside the amp if the wiring inside the speaker is OK as you say.

On the other hand, these standby transformers are known to sometimes go bad in the latest active speakers as well. I guess it could be a blown secondary winding there - the whole transformer (or the standby fuse) can't be kaput as then the amp wouldn't even turn on.

Okay,

So far I have narrowed the problem down to the display circuit board(s) of the speaker. Are there any typical issues on the circuit boards to check? The connectors between the boards are intact, the LDR functions properly when measured and there is no visible damage on the circuit board traces.

Anykind of help on how to proceed would be appreciated. Does anyone have a service manual for the MkII or III Penta?

When I was cleaning my Beolab Pentas (Mk I) I remember taking the display board out and the big cap in the display board running hot. Someone (I think Martin) mentioned that those caps are (too) getting bad and should be replaced. If some of those caps would be (partly) shorted that might cause you trouble?

Thank you Ville!

Replacing the caps worked, although they were not shorted. Now both displays work! The brightness of the displays is good as long as the display covers are not mounted. For some reason the covers are so dark that, when mounted, the displays are far too dim. Does anyone know the function of the potentiometer on the circuit board? Could it possibly be an adjustment for display brightness?

(now we do have Mk.II schematics on site - have they been recently added or did I just overlook them?)

That trimmer seems to be for adjusting the display contrast (or rather, viewing angle) of the LCD module. It won't make the backlight any brighter, but if the display seems to be brighter when looking either below or above the horizontal level, you could try adjusting it.

Apparently the backlight brightness is controlled by the LDR circuit. Try covering it and shining a flashlight on it - it the display doesn't react in any way there might be a problem with the control.

kammeri:

Replacing the caps worked, although they were not shorted. Now both displays work! 

Great work.

(Wow - perhaps my first component-level suggestion that has actually worked! )

tournedos:

(now we do have Mk.II schematics on site - have they been recently added or did I just overlook them?)

That trimmer seems to be for adjusting the display contrast (or rather, viewing angle) of the LCD module. It won't make the backlight any brighter, but if the display seems to be brighter when looking either below or above the horizontal level, you could try adjusting it.

Apparently the backlight brightness is controlled by the LDR circuit. Try covering it and shining a flashlight on it - it the display doesn't react in any way there might be a problem with the control.

That is correct, the MKII Pentas have automatic brightness control. The LDR's (or PTR's?) work without any problem though.The stupidity about them is their location as they are located behind the displays and are facing downwards. The ambient light is then measured through the front cloth but it tends to work - somewhat.

I just got informed that there has (probably) been a recall by B&O on the MKII Pentas to exchange the actual display cover for a brighter one. Unfortunately this must have taken place some 20 years ago. Tough luck [:'(] I will try to contact the former importer to verify whether this is true or not.