Denon DRA-335r

[mwk]

Hi,

I just received a Denon DRA-335r. It is playing perfectly fine, however there are some issues with it.
The first problem is that the display is flickering irregularly. Could this be a problem with the 5v line or is the display dying? I tried to find IC605 (7806), which is responsible for the 5v, but I can't seem to find it anywhere on the board.
According to the schematics it should be near by D604, D605, C644 and the bridge rectifier. However D604, D605 and C644 are not near the bridge rectifier, infact they are on the other side of the board. According to the schematics, these components also appear (?) on the Tuner side, with IC604 (7812). I do measure 5v on D604 but IC604 is running very hot, I can bearly even touch it.

Here is the service manual: http://www.manualslib.com/manual/720679/Denon-Dra-435r.html#product-DRA-335R

The second problem is the remote volume control, I can turn the volume up but I can't turn it down with the remote. All functions on the remote work, except for volume down. I measured IC251 (BA6109) on pin 5 and 6, which are Forward and Reverse for the motor. I do measure voltage on pin 5 when I press volume up on the remote, but I don't measure anything on pin 6 when I press volume down.
The remote does send out IR when pressing volume down..

Where can I start measuring? Any suggestions are welcome! 

[poot36]

If any of the ICs are running so hot that you can not touch them they are either bad or if they are a voltage regulator of some sort there is most likely a short on the output side of them.  The schematic just shows what components are connected to each other not where each component is on the board (unless there is the board tracks (PCB) layout included in the schematic that you downloaded).  Just make sure that you have the correct schematic for the particular model that you are trying to repair and that it is for the right country and region.  There can be quite a lot of differences between the same model sold in another country.  I am going to suspect a semi shorted capacitor attached to the line that powers the display backlight and potentialy powers the other circuits that are having trouble as well.  Just try to find the pare number on the silkscreen on the PCB don't concern yourself with were it is located.  Check the voltages on the chip that is getting hot as well.

[psykok]

Hi,

I had exactly the same kind of issue on my DRA-335R.
After some investigation I foud out that diode nearby the yellow cap was broken.
It was strange because when I check this diode with my dmm everything was ok but in circuit the diode was not working.


After replacing this diode the display and everything was back


Alex

[mzacharias]

I would also check the solder connections at the FL tube. This is a common problem with many makes and models.

[mwk]

OK, I poked around with my multimeter but I didn't find anything abnormal..
Anyway, I ordered replacement diodes and caps attached directly and nearby to the voltage regulator. The voltages coming in and out the regulator looked normal, but I replaced it anyway.
All solder connections look fine as well.

I will post my findings when I have the new parts installed 

[mwk]

I have replaced all diodes near the 5V circuitry and replaced capacitors C644 and C645 (couldn't find replacement for C643), but I still have the problem with the flickering display and no remote volume down.

I've pulled out the volume PCB to see if perhaps the motor driver is causing the problem, however still the same behaviour..

Here is a video of how the display flickers like a candle:

I noticed that when the amp is turned on after a few hours of non-usage the display doesn't flicker at all, but when powered off and back on it starts flickering.. Maybe the filter caps are bad?

[mzacharias]

Noise on -30 volt line, I would think.

[mwk]

I had some time for testing last night and I found out that when I pulled out CN8A (which supplies power to the display), IC604 does not get hot anymore. Input and output on IC604 stays the same with or without CN8A plugged in however.
But how can this be related together? IC604 gets power form the 19V line and the FLV display gets power from the -37.6V line (F F).

As mzacharias said, maybe there is noise on the -37.6V line?


EDIT:
Another thing to notice is that when I press and hold any button on the remote, the display stops flickering. Since the remote and volume up/down IO have RA702 as pull up resistor connected to the microcontroller, I thought maybe that shorted out. So I replaced it, but unfortunately no difference was made.. But this might indicate there still is a problem on the 5V line or VDD line, but maybe only on the logic side since I replaced all caps and diodes and the IC responsible for the 5V and VDD.
Can it be one of the transistors or caps on the logic board? I have no idea where to look, since I can't relate the behaviour of the VFD..

[mwk]

I replaced C701, C703, C704, C706 and C710 which are connected to VDD and GND. Possibly they were semi-shorted, but again no avail...

[mwk]

*Bump

[Shock]

You mentioned a few things.
1. The remote stops the flickering. Does doing the manual controls do the same?
2. It's got a heat or heat over time symptom. So test freeze spray on the overheating components in a logical order after you have worked out #3.
3. Does the symptom come up when the device is power cycled with the remote or powered off manually or after fully removing power to the whole device?
4. Measure the ripple on the power and the frequency of the flickering.