One of my Proton 320's has a problem I have not encountered before. The light sensor allows the clock display to be bright in light, but dims it completely (as in you can't see anything!) in darkness.

Assuming (possibly incorrectly) that it is the sensor, I'd like to find a replacement, but don't even know what the proper terminology is for it. I'm almost certain I have seen this item in one my catalogs over the years, but (of course) don't remember which one.

I realize I could take one of these parts off a donor unit, but 1) I don't even know if that is the source of the problem and 2) would prefer to get a new part, if possible.

thanks for any help you can offer!

UPDATE: I have searched and found the part is called a light dependent resistor or LDR. The specific one used is a VT-82L you can see the datasheet here: http://www.datasheetarchive.com/VT82L-d ... datasheets

Everywhere I have searched so far I only find VT800 series listed and it seems (I have no technical background) that the VT-82L has a specific value, which I assume has to do with the extent of the brightness and dimming it does.

Anyway - if anyone can find where I can buy these, please let me know!

If ya dont get an answer here , , please dont think the forum is snobby , , It's just that although we may have a few people up on modern TVs here , the greatest majority are into antiques , and they are a whole different world from modern TV sets ...

If a modern TV tech pops up , Great ! ... If not , you may try over at "Videokarma" , they actually have a subforum for modern flat panel TVs , so may be able to help you wether your Proton is CRT or flat panel ....

Good Luck .......

(that is , of course , if we are talkin about a TV here ??? ,,,,,, I hear "proton" and automatically think of "TV" ...... Am I correct in my guess ?)

It is a great sounding clock radio. That is why I thought this might be an appropriate forum.. Thanks for your response!

Ah , cool , a high end Clock radio , , got it .....

I know Proton makes nice stuff , I know of one of their TVs still going strong that;s been in use close to 20 years as a daily viewer , and that's why I thought TV ..... Well , if you dont turn up anything here , Videokarma has a sister site called Audiokarma that may just be the place . They deal more in the "Audiophile" stuff .....

Yes, the Proton 320 is a clock radio from 1983, almost an antique, and discussed on this forum in the past. It has a vacuum fluorescent display for the clock, mine is too bright in a dark room and I have to cover it so I can sleep.
Your photocell varies from 1.9K in light to 100K in dark, so try a small 100K pot in parallel so you can dial in a value that gives you the brightness you need, then measure the pot and replace it with a small resistor of the same value.
The usual question we get is how to replace the dead pilot lamps, powered from 12 volts DC. I used two green LEDs all in series with a 470 ohm resistor.
Don

Thanks Don - I'm very familiar with the dead pilot lamp issue, but have always used a bulb. I don't really understand what "in series" is, or what "trying a small 100k pot in parallel" means. I also have meters, but don't know how to get measure a pot. What I'm saying is, I can solder, but other than that, I need step by step instructins to do things like the ones you have suggested.

If you, or anyone else on this forum wants to coach me on this, that would be great. If not, I would certainly understand. In the past I've generally done this off-list, either in email correspondence or over the phone.

In any event, thank you for your advice!!

Michael

Michael, At first I figured this was a non-starter, then I realized you can get a pair of mini-clip jumper wires and clip the ends to the two leads of the photocell. If your meter has clip leads, you can use them, unplug them from the meter. Now you can easily try various resistors by clipping or wrapping their leads to the other ends of the two jumper wires. Try anything from 100K ohms down to 5K ohms. Turn off the room lights and see how bright the display is. When you find the brightness you like, unplug the radio and solder that resistor to the two leads of the photocell. Look for a small resistor that will fit easily, 1/4 watt or 1/2 watt)

(The case has gray plastic dial cover, so it won't be as bright when you assemble it later. Remember to clean the inside of the dial cover with a damp soft cloth and wipe the display, it will get rid of the haze)

Don

Thanks Don - So leave the photocell soldered to the board and clip a wire to each "stem" then connect the other end of the wire to various values of resistors?

Assuming I am understanding you correctly, the photocell has foam tubes on each stem (I assume this is insulation), but I will try to get enough contact to try this. Once I have found a resistor of a suitable size and value, then what? Solder it between the two stems of the photocell? On top of the circuit board, or underneath?

(I tried to send you a pm, as this has become a conversation between the two of us, but for some reason it did not work. If you wish to pm me, we can continue the discussion that way, or I can send you my email address).

many thanks for your patience regarding my lack of knowledge about these things,

Michael

Michael, the PM section of the forum is broken now. You can remove the insulation with a razor or box cutter or exacto knife. Solder the resistor across the leads of the photocell wherever you can fit them. Maybe you can spread the leads a bit on top to get room, or put one resistor lead higher on one photocell lead and the other resistor closer to the board, so the solder joints don't hit. Fold the resistor lead around the photocell lead like a letter J hook, then squeeze it with a pliers so it stays in place, then give it a Quick spot of solder so you don't damage the cell.
Don

Sounds good - mini-clip jumper wires and a bunch of resistors varying in value from 5k to 100K. Once I have those and some time, I will give it a shot. Thanks so much for all your patience and help!

Proton 320s all pretty much have that problem by now, although most of them don't go completely dark, in the dark. The usual problem is just that it dims too much and the digits are unevenly lit. And the recommended fix is indeed what works. You'll have to experiment with different resistors, but then just solder them across the photocell on the back side of the circuit board. It's a small space but just be careful and use a low-wattage soldering iron.

For the dial lights, I use grain-of-wheat lamps from Radioshack - perfect fit for that space and the way they are mounted.

Thanks Jeff! I have several of these radios and definitely have found that a common problem, but I've only had them dim unevenly, which I don't consider a problem.

What value grain-of-wheat lamp from Radio Shack do you use? I guess I will go to Radio Shack for the resistors, since I have no clue which one will work and things are returnable if unused. Any particular assortment of values you recommend?

thanks again!

Michael

It's been over a year since I did the last one and frankly I can't remember the value of bulb, but if I remember correctly it's six volt, or maybe nine. Clip the old bulb out and with the radio on, measure the voltage. Then take the old one to Radioshack and you'll find the perfect size. I use Duco cement to just glue them into the little trough.

While at Radioshack, you can buy a small pack of assorted 1/4 watt resistors for just a few dollars.

The power to the lamps is 12 volts DC, uses 12 volt lamps.
Don

thank you Don!

Since you are going to Radio Shack, you can get this miniature 100K ohm pot instead of the bag of resistors. Just connect to the center leg and one end, turn it to get the desired brightness in a dark room, and leave it in the set, it is very small. You can then change the setting in the future.
http://www.radioshack.com/product/index ... Id=2062302
Don

great idea! connect as in solder the center leg to one lead and one end to the other lead from the photocell?

thanks again!

Yes, it will probably be easier to use two short pieces of thin wire to make the connections, and if you can solder the wires to the back of the board, you will avoid the chance of melting the photocell.
Don

Thanks. I understand!

Hi Don - it worked like a charm! The feet of the pot were spaced perfectly to match where the two leads from the photocell came through the bottom of the board. I did not use wires. There was enough room to accomodate the pot when the board was screwed back into place.

Thanks for all your help!