Oven LCD display dim and uneven

[sam_sam_sam]

Re: Oven LCD display dim and uneven

Look at the soldering joints on the display pins and if the soldering joints are not shine then remove the solder form each soldering joints and resolder each joint and see if this makes any difference in the display

Also replace all the capacitors on this board as well

[gjkozy]

Re: Oven LCD display dim and uneven

I am having the same problem with control board #3116090102. Going to try the cap route and inspection. After reading through the thread, I hope that I have better luck.

Seens that I have to purchase caps in batch quantities. My cap values match those listed in the thread. Good job on making your problem and approach clear and conconcise. The pictures and list are helpful.

[tester272001]

Re: Oven LCD display dim and uneven

perhaps check the VFD display solder connections to the main board? if you can inspect them wth a magnifying glass. You might see solder joints that are cracked. reflowing the joints with some 60/40 might help if they are losing conductivity.

[electri-calvin]

Re: Oven LCD display dim and uneven

I solve such problems by soldering panel component

Can you elaborate on this???

[electri-calvin]

Re: Oven LCD display dim and uneven

What do you mean you "fixed such problems by soldering panel components"? Did you just re-solder the VFD display ?

[Hafizit]

Re: Oven LCD display dim and uneven

I solve such problems by soldering panel component

[R_J]

Re: Oven LCD display dim and uneven

The displays to wear out, they loose emission similar to a crt in a tv. The display is brighter over the heater wires which makes sense. The display tube should be a 100% vacuum but that can also change over time as a bit of air gets in.
You might try someone that deals in used appliances, you might find a used panel or a similar panel with the same vfd.

[GA Novice]

Re: Oven LCD display dim and uneven

I am ready to throw in the towel. I replaced all the caps and the display remains the same. The attached picture shows the issue, bright in the horizontal center, dim vertically above and below. All the connections appear good. All the cathodes glow red. I was unable to test the actual voltage of the cathodes and anodes while connected to 120v AC as I did not want to touch the wrong part and short it out. Not sure what the issue is other than the display is just worn out. If the entire display was dim, or blank, that would lead to a faulty part. But with it uneven, I am thinking it is getting the proper voltages but the display is just worn out. Any other thoughts appreciated. Thanks.

[R_J]

Re: Oven LCD display dim and uneven

I think you are refering to the heater filaments voltage for the vfd, it is usually about 3 volts ac. The heater pins are usually located at each end of the display.
here is more information https://www.explainthatstuff.com/how...lays-work.html
Regarding post #21 the dark spot is the result of the GETTER See this: https://en.wikipedia.org/wiki/Getter

[petehall347]

Re: Oven LCD display dim and uneven

sorry i do not understand how these work . i do read a lot though out of interest and the AC supply is what lights it up . well thats how i see it .

[GA Novice]

Re: Oven LCD display dim and uneven

AC for the display to light up

The display gets power, but it is dim and uneven. What specifically should I test? (ie, What on the display board should I test with the multimeter?). Sorry for the basic questions. The spark module works so the Power board is likely passing along 120v to the spark module.

[petehall347]

Re: Oven LCD display dim and uneven

AC for the display to light up

[GA Novice]

Re: Oven LCD display dim and uneven

is the AC drive good ?

Not sure, how do I test that? The range works normally, the gas burners light up quickly, and the gas oven is strong. Since its a gas range, it does not use much AC. Thanks.

[petehall347]

Re: Oven LCD display dim and uneven

is the AC drive good ?

[GA Novice]

Re: Oven LCD display dim and uneven

I went ahead and tested the diodes, and all were good. One tested funky in circuit, but after pulling it, it tested good.

I then pulled the three very small caps on the display board (I already changed the caps on the power board) to see if they were good, and I got the following:

- 4.7uf 35v tested 4.87uf with an ESR of 11 ohms
- 0.47uf 50v tested 0.433 with an ESR of 13 ohms
- 10uf 16v tested 11.14uf with an ESR of 9.2 ohms

All three tested within specs, although the 50v is on the low side. I plan on replacing all three in the next week or two but its looking like the problem is not the caps.

I then checked the solder connections, and all looked good except for one of the pins for the horizontal VFD filaments. I re-soldered that pin but the display remained the same.

Aside from changing out the three small caps on the display board noted above, I think the next step is to test actual voltage going into the VFD with the board plugged into AC power. That will identify if the issue is a lack of power getting to the VFD or if the VFD itself is faulty. Thanks for any suggestions.

[GA Novice]

Re: Oven LCD display dim and uneven

I think I figured out the location of the rectifier. There are several diodes near the large caps, named D1, D2, D3, etc. I believe those are the rectifier diodes. Thanks.

[GA Novice]

Re: Oven LCD display dim and uneven

I pulled the board again to get the specs on the caps on the display side. The picture above of the display is not mine, I found that on the internet. The picture in this post is the display side of my board. At first I thought there was a problem due to the dark spot in the upper left of the display, but the picture above has the same spot so I am assuming that is part of the design.

The three caps on the display side are small:

0.47uf 50v 105c (to right of display)
4.7uf 35v 105c (lower right of display)
10uf 16v 105c (bottom left of display board)

A vacuum fluorescent display post I found online had a faulty 1uf 50v capacitor, so I am crossing my fingers the issue is one of these three small capacitors.

All of the connection appear firm, but I will check those when I replace the caps hopefully in the next week or two. As I indicated above, the board is two levels connected with a series of metal pins, and to access the solder side of the boards requires bending those pins 90 degrees to get the boards to lay flat. I am afraid to bend the pins too many times for fear of damaging them or their solder connections.

Another possibility I found on the internet which is above my pay grade is a faulty diode in the rectifier. My knowledge of rectifiers is zero but I assume this board has a rectifier as AC is being converted to DC at some point. Due to my lack of electrical component knowledge, I am unable to identify the rectifier to test it. A few more YouTube videos and I will figure it out.

My plan is:
1. Replace three small caps on display board.
2. Figure out if there is a problem with the rectifier.

3. Test connections and re-solder as necessary the power connections from the display back to the transformer.

Thanks for your thoughts and help. I appreciate it. I will update again in a couple weeks.

[GA Novice]

Re: Oven LCD display dim and uneven

Thanks, I will try these suggestions.

[redwire]

Re: Oven LCD display dim and uneven

My $0.02 I see horizontal stripes, vertically bright and dim bars across the entire VFD.

This points to the VFD filaments which are the six thin horizontal wires across the display, if one wire has low emission then you get a dim stripe. It could be age or a bad connection or weak bias voltage.

I would resolder all VFD filament connections, from the tube back to the other board and transformer. They are low voltage and high current, and the VFD pins are Kovar which tends to make a poor connection with age. Your display is way crooked so it got whacked.

The VFD filament pins are at each corner grouped as three pins. Follow jumpers W33, W32 "FIL" to where they cross over to the power board. They should go to a transformer winding. I would resolder all those connections in the chain.
Beyond this, need to have some idea of the circuit for the VFD bias.

[R_J]

Re: Oven LCD display dim and uneven

I do see a couple small caps (C3) near the display, They may not have anything to do with the display but might be worth checking.