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Old 09-12-2018, 03:04 PM   #1
GA Novice
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Default Oven LCD display dim and uneven

I have an 18 year old Frigidaire range (combo oven and cooktop). The display (part number 316080102, no longer in production) is dim and uneven. It looks worse than in the picture. The red letters in the upper right of the display are particularly dim, this is where the temperature is displayed. I opened up the control panel and the caps do not have obvious tell tale signs of failure. There are 4 caps - 100uf 50v, two 470uf 16v and 3300uf 16v. Do you think the caps are bad (and if so which one), or is this a sign the LCD display is bad? Thanks for your thoughts. Pictures below.
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File Type: jpg IMG_4079[1].jpg (391.0 KB, 31 views)
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File Type: jpg IMG_4077[1].jpg (446.2 KB, 12 views)
File Type: jpg IMG_4070[1].jpg (341.6 KB, 10 views)
File Type: jpg IMG_4071[1].jpg (372.8 KB, 12 views)
File Type: jpg IMG_4073[1].jpg (344.1 KB, 9 views)
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Old 09-12-2018, 03:13 PM   #2
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Default Re: Oven LCD display dim and uneven

I would suspect the 50 volt caps would be for the display voltage which shouild be around 25-30 volts dc. or it could be the 3300 which is likely the main filter cap. Without a cap/esr meter to check them, I would just replace all of them, if that does'nt fix it it could be just the age of the display itself

Last edited by R_J; 09-12-2018 at 03:16 PM..
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Old 09-12-2018, 07:14 PM   #3
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Default Re: Oven LCD display dim and uneven

Yeah, the cap date codes are from the year 2000, it's a safe bet that they starting to dry out, especially being next to that transformer and most likely operating 24/7. They look like Elna caps, which are a good brand, although any caps can fail when their time is up.

The display looks like a VFD (vacuum fluorescent display) rather than LCD or LED. They can also go dim over the years, although I had seen 1980s car dashboards where the VFD is still in good condition, as well as VCRs and stereo equipment of similar vintage.
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Old 09-12-2018, 07:55 PM   #4
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Default Re: Oven LCD display dim and uneven

Thanks for the comments. I am going to change the caps and see if that does it. Also, I realized this is in the wrong forum, it should be in the Other Wierd Devices, if a mod could move this there, thanks.
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Old 09-23-2018, 01:26 PM   #5
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Default Re: Oven LCD display dim and uneven

I changed the caps and no dice, display is still uneven. Looks like the VFD is worn out. The old caps all tested good except the ESR was a little higher than the ESR of the new caps.
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Old 09-23-2018, 02:04 PM   #6
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Default Re: Oven LCD display dim and uneven

Are there any caps on the display board itself? It may use a small dc-dc converter circuit elsewere.
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Old 09-24-2018, 11:07 AM   #7
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Default Re: Oven LCD display dim and uneven

The board has two levels. The bottom level has the caps, the top level has the display. The two boards are connected by a series of metal wires on one side. The solder side of the boards was difficult to access, I had to slowly pry the boards apart (bending the metal wires) to access the solder holes for the caps. Picture attached showing the inside of the two boards and the new caps installed. I didn't focus on the top level when I had it out. I found a picture of the top level on the internet and it is attached. It does not look like there are any big caps on the front, just two very small ones. Do you think those small ones could be the issue?

The attached picture has a very clear image of the display (not my actual display). The part of my display that is the weakest is the oven temp in the upper right corner. Looking at the picture, it looks like the oven temp is in 3 separate cells. So it must be the horizontal aspect of the display that is faulty. In a picture in my original post, the BAKE light is still ok, which is in the bottom of one of the cells of the oven temp. So I think the issue is the part of the VFD display that is horizontal. Time to do some VFD research.

I will add that this oven is hardly used. So although it is close to 20 years old, the oven temp is rarely illuminated. The clock is always on, and appears to be brighter than the oven temp, even though the clock has been illuminated for close to 20 years.

Thanks for any suggestions you may have.
Attached Images
File Type: jpg IMG_4185[1].jpg (573.5 KB, 13 views)
File Type: jpg IMG_4188[1].jpg (583.6 KB, 16 views)
File Type: jpg front oven control.jpg (184.5 KB, 20 views)

Last edited by GA Novice; 09-24-2018 at 11:17 AM.. Reason: added detail
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Old 09-24-2018, 11:44 AM   #8
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Default 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.
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Old 09-24-2018, 01:46 PM   #9
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Default 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.
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Old 09-24-2018, 06:38 PM   #10
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Default Re: Oven LCD display dim and uneven

Thanks, I will try these suggestions.
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Old 09-29-2018, 02:48 PM   #11
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Default 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.
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Old 09-30-2018, 08:02 AM   #12
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Default 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.
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Old 09-30-2018, 07:07 PM   #13
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Default 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.
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Old 09-30-2018, 07:43 PM   #14
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Default Re: Oven LCD display dim and uneven

is the AC drive good ?
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Old 09-30-2018, 07:45 PM   #15
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Default Re: Oven LCD display dim and uneven

Quote:
Originally Posted by petehall347 View Post
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.
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Old 09-30-2018, 08:00 PM   #16
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Default Re: Oven LCD display dim and uneven

AC for the display to light up
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Old 09-30-2018, 08:11 PM   #17
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Default Re: Oven LCD display dim and uneven

Quote:
Originally Posted by petehall347 View Post
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.
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Old 10-02-2018, 05:58 PM   #18
petehall347
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Default 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 .
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Old 10-02-2018, 06:20 PM   #19
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Default 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

Last edited by R_J; 10-02-2018 at 06:24 PM..
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Old 10-15-2018, 11:52 AM   #20
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Default 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.
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