VHS repair???

pdm4606

Super Member
I have several VHS players and they seem to have a common problem. The problem is that the front information panel is very dim on several and is getting dimmer on others.
Is this a simple fix like a power cap. problem or is the panel failing?

I did have a similar issue on a graphic equalizer several years ago and fixed that by replacing a leaky electrolytic.

Paul
 
I'm going to guess the cheapy VFDs are just wearing out especially in newer models.
 
The displays do age. The hot cathode loses emission just like any vacuum tube.

However, they often use DC-DC converters to generate the high anode voltage, and they fail prematurely due to dried up electrolytic capacitors.
An easy & wothwhile TRY is to replace all electrolytic capacitors around the display drive circuits.
 
Looking at stuff...

The VHS is a Panasonic PV-4651. Not that old.
I checked the circuits around the power supply board and they LOOK ok. I am having trouble getting voltage readings. Need a schematic to do that properly. So many things change in different actions.
I notice one thing. The readout display is around a 1" by 2" assembly at the front. I can see what looks like a smear from a flash or other in one corner of the assembly. Of course it is under the glass and inside and not accesable. I wonder if that is an ambient light sensor and is clouded over giving the sensor a reading of a very dark enviroment making it's display to be Dim??? There is a small button with leads under the clouded section, inside of course.
I will look for a schematic.

Paul
 
at the front. I can see what looks like a smear from a flash or other in one corner of the assembly.

That is the 'getter', an area where they evaporate a reactive metal like barium onto the inside of the glass. Its function is to mop up any stray gas molecules after evacuation of the tube. If the vacuum is lost, the getter oxidises and turns white.

Failing capacitors do not show any visible signs of damage or degradation.
 
I have a Sony LD player that had a dead VFD, it was a bad cap on the display board (someone here at AK tipped me off to that) well worth the time to check out that possibility.
 
Whwn replacing switch modde power supply caps, be sure to replace with the correct type and heat spec.
 
Checked power caps....

On the power supply board and they were all in range. All 8.
Then I found 3 small resistors on the bottom board that have had some heat at one point. Very small resistors. Very close to the display connector.
I un-soldered them and found one way out. I can't find a schematic but I am replacing with an order for an assortment due in a few days.
The questionable cap is color coded to be 10 ohms(I figure it is used to slightly lower the voltage going to the display??).
Checks 94.6 ohms. Hope I figured the color code right.
I can't believe I didn't have anything to replace it with. I would take a chance with a close ohm but it is a job to put the unit back together again if wrong direction. Closest res. I have is well over 100 ohms, not better than what is now in.

Paul
 
Be very sure it IS meant to be 10 ohms and not 100 ohms.

Heat can make the colour bands change colour. Putting in 10 ohms where 100 is needed could burn out the display tube forever.
 
Good luck with the resistor diagnosis. When that doesn't fix it then look further into which bad capacitor is causing it with an ESR meter. It will likely be one on the secondary side of the SMPS with a higher voltage value maybe 35 or 50 V than the others that may be 6.3, 10, 16 ... high ESR failure can read fine with a capacitance meter. Over and out.
 
It works...

I got my shipment of resistors and quickly installed the 10R in place of the suspected blown R.
It worked. My guesstimate was right. The value had changed on the old R and even though it was discolored and burned changing the color code I got the right one.
I may go to a 12R as the brightness of the display is extreme.

Thanks again for all your assistance.

Paul
 
Some photos...

See the photos enclosed.
If anything it will give folks an idea and be able to fix theirs.

Paul
 

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