Realistic SCR-8 VU Meter Replacement

[cmaitner]

Greetings, just picked up a very nice SCR-8 but I noticed a couple of the VU meter lights not as bright as the others. Is that something that I can fix? I have another VU meter board that works well but I'm kind of scared to try and replace it. Does anyone know if I can replace the meter board easily?

Thanks for the help,

Christian

 

[cmaitner]

It looks like I can take out the other VU meter from my junk SCR-8 boombox pretty easily, except I don't want to re-solder the wires to the board. So, maybe I can cut the 4 wires and just splice them with connectors? I think it could work... does anyone know a better option?

 

[Superduper]

No, resolder them, it's the right way to do it and if you don't know how to solder, this will be a good time to learn it. Furthermore, the leds that aren't as bright as the others is probably simply a matter of dropping resistors that have drifted in value.

 

[cmaitner]

No, resolder them, it's the right way to do it and if you don't know how to solder, this will be a good time to learn it. Furthermore, the leds that aren't as bright as the others is probably simply a matter of dropping resistors that have drifted in value.

Thanks Supeduper! how would I "drop resistors that have drifted in value"? Not sure what that means.. thanks

 

[Superduper]

LEDs are low current devices and typically require that they be run in series with a "dropping" resistor, which is basically a resistor who's value is carefully selected to pass a safe current level (based on specifications of the led, and the desired brightness level). The term "dropping" just means that it's purpose is to drop the current being passed. Over time, resistors can increase in value and this may cause drop in led intensity. Usually, they are a row of resistors that all look identical (10 leds will have 10 resistors). If you can locate the row of resistors, and they all look the same (same color bands), test them with a digital multimeter to see what they read. If you find one reading significantly higher in value than the others, it's probably bad. Replace it and the led brightness should all match again.

 

[cmaitner]

LEDs are low current devices and typically require that they be run in series with a "dropping" resistor, which is basically a resistor who's value is carefully selected to pass a safe current level (based on specifications of the led, and the desired brightness level). The term "dropping" just means that it's purpose is to drop the current being passed. Over time, resistors can increase in value and this may cause drop in led intensity. Usually, they are a row of resistors that all look identical (10 leds will have 10 resistors). If you can locate the row of resistors, and they all look the same (same color bands), test them with a digital multimeter to see what they read. If you find one reading significantly higher in value than the others, it's probably bad. Replace it and the led brightness should all match again.

 

[cmaitner]

Great thanks!

 

[Tinman]

I'm not sure but it doesn't look like there's a resistor for each LED.
Is it possible that the LEDs have just dulled over time?
Op, I'd solder the other board in if those are fully working.
It'll be extremely easy with just four wires.

 

[Superduper]

Ok in your case, since you have an extra meter module, that would definitely be easier.

As for whether an LED can dull over time, maybe, I usually just see them burn out entirely. Or it's also possible that one bulb burned out & someone replaced just that one LED. If that's the case, it's entirely possible that one will illuminate with a different intensity since LEDs specs all over the place with respect to mcd ratings, so it's very difficult to get an exact match which is why it's typically recommended to replace all in an array at the same time unless it's just something for a stereo indicator.

 

[cmaitner]

Great! Thanks guys! Looks like its only two LEDS of the total 24... the Left #1 and Left #4 are somewhat dimmer than all the others. I suspect most people wouldn't notice it but I would like to get the VU meters perfect at some point, that's just me. I may just wait to repair after I have enjoyed using the boombox for a while, as it's still in pristine condition now. I also noticed my backup sound meter board does look better overall as far as equal brightness of the LEDS, so I may just install the replacement board sometime down the road.. it's only 4 wires so I probably will just solder the 4 wires to the new board. It's also tough to open the SCR-8 because the cassette door doesn't come off easily and often breaks. But I feel like it would be fairly easy overall so thanks for that...

 

[Tinman]

I know they can be tough but if you put even pressure on the door (remove the clear plastic first) they shouldn't break.
You want the plastic "hooks" to hit at the same time when it slides up.
Most people man handle it and do it crookedly (is that a word?) which is why they break.
Maybe even a squirt of silicone on each hook might help them slide easier.
Nice you have a backup board for future use.

 

[cmaitner]

yes good to hear, it's just frustrating because I see old beat up SCR-8's that have perfect LED lights and mine is fully restored and pristine but lights aren't perfect..lol