Red Lines on VFD - DVD Player Stopped Working

[paul_g_787]

OK, voltages as follows.

0VAC / 3.6V DC between the two 3.5V AC pins
STBY is at 5.87V DC and 2.12V AC

I am confused by these two... 


-24V is at -24.5V 
5v-ST is at 4.95V 

+5V is now at 5.0V DC 
+12V is at +12.6V DC
-12V is now at -12.5V!! DC

No AC measurements to be seen on these DC rails.   

I reckon it is time to connect it back up and see what happens.?

[james_s]

3.6V DC on the 3.5V AC suggests that the earlier hypothesis is correct, that the AC filament voltage is developed by the microcontroller or some other circuit switching a H-bridge. For some reason that is not happening so the output is just stuck at DC. You might see if you can find the microcontroller and check for voltage at that, I would expect it to run from 3.3V although it may be 5V. Check the reset pin if you can locate it and also the clock. The tricky thing about servicing stuff like this is you generally don't have a schematic so there is a lot of guessing involved.

[paul_g_787]

OK so I connected the board up to the player and when you power on the device the 3.6DC Voltage goes away and a 3.6V AC voltage appears..

When you put the player in standby mode this reverts.

So I would guess that the main board tells the power supply to start switching?   

Regardless, good news!! The player powers up, the disc spins and the VFD is un-harmed and working great 

I am going to pop the lid back on an connect to the TV and see if I get a picture.

[paul_g_787]

Some very good news! It is working just fine 

The VFD does appear to be a little brighter than I remember. But all appears to be well.

I will pop it open again in a few months and perhaps change those other slightly high ESR capacitors.

I have certainly learned a bit more about switch mode supplies from this and also about how VFDs work.

[Gyro]

Well that was a rather better than expected result! 

The amount of wiring might be a little excessive (it's very modular) but it looks pretty well constructed. I can't help noticing that large heavy slotted ferrite on the wide ribbon going to the front panel. It is glued to the PSU output ribbon very close to the srbp material PCB, it's just possible that it might have encouraged a cracked trace. It's been working for a very long time since it was shipped though.

I guess keep and eye on it and enjoy meantime.

[paul_g_787]

The ribbon with the ferrite on it is going to the SD / CF card reader / USB port on the front panel.

No cracked traces as far as I can tell.