Denon AVR-2700 no display

[Caleb]

Re: Denon AVR-2700 no display

Everything in the rc network tests fine, I think Im left with the conclusion that the driver ic is bad. Will have to see if I can find a parts machine for a donor.

[R_J]

Re: Denon AVR-2700 no display

That 9 volt difference between the -33 and the filament (-24) is created by zener diode D104 HZS9B.

[Longbow]

Re: Denon AVR-2700 no display

If possible, zoom into the FL display area of the schematic. You need to draw a simplified diagram of how an FL works. It is a vacuum tube.

The filaments still have not been tested. They are usually around 3 volts, and can be either AC or DC. The filaments are not referenced to ground, they are referenced to the -33 volts, or in your case perhaps to -24 volts. In other words, you will see a large negative voltage on the filament pins of the FL (extreme outside pins) referenced to ground. That would be your "cathode" voltage. But to measure for filament voltage you have to measure directly between F1 and F2. Also be sure to check for filament continuity (with the power off and one filament connection open).

The segments of the FL are multiplexed by the IC. A segment will light up when its pins are held low (zero volts) and will turn off when the voltage is -33v. For a lighted segment, current will flow from the -33 volt filament to the zero volt segment (plate). A random check of the segment driver pins on the IC should show Zero to -33v. multiplexing pulses.

Typical failures include the diode and capacitor in the filament supply if it is d.c. Or, the -33v supply capacitors which are the most sensitive to power spikes. Sometimes the -33 volts comes from a miniature switching supply near the display.

Note that all FL displays slowly get dimmer with age. If you have the full segment voltages present and the display seems correct, but is just very dim, it is possible that it is simply worn out.

[R_J]

Re: Denon AVR-2700 no display

This display gets its 3 volts ac directly from the main power transformer, easily measured with a meter, don't you wish you had a scope

[budm]

Re: Denon AVR-2700 no display

The filament ( which is Cathode) voltage is around 3VAC or so, you can measure it right at the two brown wires from the transformer, it must be getting filament voltage otherwise you will not see the display on the screen. It looks like the segments are not driven properly by the IC.

He must be getting the filament other wise there will be no display at all due to no electron emission from the Cathode.

[Caleb]

Re: Denon AVR-2700 no display

RJ I have a few scopes , and yes I had tested this as noted in the above posts. I gave this back to the owner as he didnt want to out another 60$ for a parts unit, it plays music just fine it just is a royal pain to navigate to the correct input and or station. Many thanks to all of you who helped with the diagnosis.

[bcstedt]

Re: Denon AVR-2700 no display

I'm having a similar problem with a Denon AVR-587. Since the symptoms and system are very similar should I post details here or in a new thread?

AVR-587 (2006)
Sanyo LC75721E display driver

AVR-2700 (1999?)
Sanyo LC75711NE display driver