Denon AVR-2700 no display

[Caleb]

Have this unit in for repair. Initially it went into protect, I found and replaced a 5v reg and a 12v reg and it now powers up and plays music. However the display just barely lights and doesnt display anything. I have 5v to the vcc of the ic that controls the display, -33v on the other feed pin and -24v to the outside rails of the display lcd. I am thinking the ic is bad, however I have not ever run into that before, am I missing something here? All the buttons on the front work, and volume control works as well. schematics for this portion of the circuit attached. I see a pin labeled chip enable, does anyone know what signal this requires?

[budm]

Re: Denon AVR-2700 no display

How about the filament voltage?
Can you upload the service manual so we can look at it?

[stj]

Re: Denon AVR-2700 no display

i'm willing to bet the display drive involves an electrolytic.
i used to see this all the time on VCR's
i cant remember what the cap did, but i used to replace them with a 1uf multi-layer ceramic and they never failed again.

i see an electrolytic in the foto to the left of the display!

[Caleb]

Re: Denon AVR-2700 no display

I tried to upload the service manual. Its over 20 mb, I'll try to get a working link for you. I put it up on ET but it doesnt show up now. Is the filament voltage on the ends of the display? If so -24v. I will swap out that cap when I get home tonight and see if that does the trick. thanks for the ideas.

[jetadm123]

Re: Denon AVR-2700 no display

In your first photo, is that cap directly under the display leaking on the bottom? Or is just the lighting?

[Caleb]

Re: Denon AVR-2700 no display

No its not leaking, its left over dust around the cap, this must have been in a garage as it was filthy inside

[Caleb]

Re: Denon AVR-2700 no display

I put in two new caps just below and to the right of the display, and have same symptoms. Budm sending you a Pm with a link to the SM

[budm]

Re: Denon AVR-2700 no display

OK, I am downloading it from HIFIENGINE.

[budm]

Re: Denon AVR-2700 no display

OK, look at the pin out of the FLD on service manual page 28 (not the PDF page), you will see F1 and F2 for the filament, the power transformer (the two brown wires, on page 55) supplies the filament voltage, see service manual page 53 connector CN025 (not sure about the last digit).
If you look at the darkened room , you can actually see orange glow of very small wires inside the display.

[Caleb]

Re: Denon AVR-2700 no display

F1 and F2 were where I measured -24v, I think that portion is working ok as it does light a little, like its primed and ready but receiving no data to display. I took a picture of it in a dark room attached below

[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.

[Caleb]

Re: Denon AVR-2700 no display


Ok i will check for ac voltages, should have thought of that since those feed wires are coming straight out of the transformer. but it looks like we may be back around to a def ic anyhow

[budm]

Re: Denon AVR-2700 no display

I believe you must be getting the filament voltage, otherwise the display will not glow like that.

[Caleb]

Re: Denon AVR-2700 no display

Any likelihood that one or more of those little transistors next to the ic could cause a fault like this? I guess I will rig up some test points for the cricket and test them out anyway.

[budm]

Re: Denon AVR-2700 no display

From looking at the pictures, the dot matrix display has all the dots glowing? The other section seems nice and bright, I.E. TUNER, DVD indicators.

[stj]

Re: Denon AVR-2700 no display

the driver chip has an interesting pin on it marked VFL - i cant see where it goes but it's an interesting thing to check.

[Caleb]

Re: Denon AVR-2700 no display

While it seems bright in the picture it is not when viewed in normal lighting, and even more so after the tinted plastic cover goes back on. You really have to look carefully to see its on. My next question.. is this going to be a proprietary ic to drive the display or is it a standard display driver

[budm]

Re: Denon AVR-2700 no display

One thing is that you have -33V and -24V which is the difference of about 9V so I am not sure that is enough difference potential between the Cathode and the Anode to give out enough brightness. I will need to look at the spec of the driver to see what it should be. VFD (Vacuum Fluorescent Display) operates in the same way as Vacuum tube , Cathode, Grid, Anode (Plate).

[Caleb]

Re: Denon AVR-2700 no display

I was looking at the vfl and I believe I tested it at -33vdc. when comparing pinouts I noticed a discrepancy between the schematic and the pinout so I pulled the datasheet and the schematic is correct, also noticed the resistor capacitor network to run the clock, will have to test that when I get home.

[jetadm123]

Re: Denon AVR-2700 no display

I took a very quick look at the owner's manual. If you select the setup button on the front panel, it should display a system setting menu that allows you to change panel brightness. May/may not work, since the manual covers several different models.