XL Series Power LED Failures?

[+Larry]

I have several 600/800 XL's that have issues with the power LEDs. A couple don't work at all, and one blinks off-on. Are their any known issues with the LED's or its specific circuitry? I haven't dug into this yet, and thought I'd hopefully collect some info as to the possible causes.

 

Thanks,

Larry

[flashjazzcat]

Sometimes the traces break off the back of the board, or the solder simply fractures. It's also possible for a break in the ribbon cable to cause this issue. Usually resoldering the LED or replacing it with a new one fixes it.

 

Oh: and on the keyboards which use a dual-layer mylar sheet, the LED legs make contact with the traces via (IIRC) two conductive pads. Sometimes the traces on the mylar need touching up on those ones.

Edited June 15, 2015 by flashjazzcat

[bbking67]

Check the keyboard ribbon cable. If everything looks good, try reseating.

[+bob1200xl]

I have noticed that the LEDs on a 1200XL seem prone to failure. Evidently, the tinning on the LED leads is poor, which results in a poor solder joint. A little attention to the solder adhesion and all looks well. Perhaps the other XLs suffer from the same issue.

 

Bob

[flashjazzcat]

The PCB to which they are soldered is also very fragile. I made some modifications to the LED circuit and the traces vaporise with very little encouragement.

[Bryan]

On the 600/800XL's with mylar keyboards, the LEDs are simply touching the conductive paint which oxidizes and turns black with age. Eventually, the contact points won't support the 15-20mA or so they need.

[+Larry]

Thanks, guys! Really informative answers that should help a lot!

 

-Larry

[Bill Lange]

A few months ago, the power LED went out on one of my 600XLs. I removed the LED and put a new one it and still nothing. I then bench tested both LEDs and they both worked fine. The problem seemed to be elsewhere. I took one of the LED and tinned the leads with solder to give it a bigger area to make a connection. I pushed it back down into the LED socket and it seems to be holding up for now.

 

Bill

[Tillek]

Not to be Captain Obvious... But just for the record, did you test them all with separate power supplies? Or did you plug them in to the same one (or two)?

 

I know it sounds stupid, just thought it should be ruled out and didn't see any mention of it in the thread.

[Timothy Kline]

I have a 1200XL that I've verified has fried LEDs. I know nothing of the history of this one, having bought it recently, but I'm surprised that all 3 LEDs look as though there is a broken filament inside them. Someone reversed voltage to the LED board at some point maybe? Continuity was fine across the LED board, and the ribbon cable also checked fine for continuity.

 

I have two questions for the forum:

 

1. What do I need to look for as I shop for replacement LEDs? 5v LEDs, since the 1200XL is 5v-based? Is there additional identification I need to look at for compatibility in the 1200XL?

 

2. Should I bother replacing them (well, the Power LED will need to be, at a minimum) since installing the Ultimate 1MB--from what I've seen here on the forum--will break the functionality of the LEDs. (Before I found that out, I had planned on maybe experimenting with diverse colored LEDs: Red, for Power LED, White, for International, and then a toss-up between between blue, green, or even purple for the remaining LED.)

 

Thank you, in advance!

Tim

[flashjazzcat]

Standard common or garden 5mm LEDs will do: voltage drop is handled on the motherboard. They'll flash pretty patterns with U1MB when software writes to PORTB to bank extended RAM, although you can rewire them if you're feeling adventurous. Mine are power, internal HDD ON/OFF, and HDD activity.

[KLund1]

 

Need to bring back a old thread.

I also have a 1200 with verified dead LED's.

 I can not find 5v 5mm red LED's. 

Anyone know where to get proper replacement?

Thanks

[BillC]

1 hour ago, KLund1 said:

 

Need to bring back a old thread.

I also have a 1200 with verified dead LED's.

 I can not find 5v 5mm red LED's. 

Anyone know where to get proper replacement?

Thanks

The dead LEDs aren't actually rated +5V, resistors are used to limit the voltage/current to the desired value.

The 1200XL schematic shows 220 ohm limiting resistors for all 3 LEDs. These resistors can be changed to

compensate for different LED voltage/current requirements.

 

Edited March 17, 2023 by BillC

[TGB1718]

Generally Red LED's have a forward voltage drop of about 1.8V so if you know

the forward voltage drop, it's easy to calculate the resistor value for a given current.

Depending on how bright you want the LED 10 to 15 mA is sufficient.

 

So subtract the forward voltage from the supply i.e. 5-1.8 = 3.2

using ohms law r=V/I so 5/0.15 = 213 Ohms so 220 Ohms is good enough.

 

If you use different colour LED's, the forward voltage will be higher so the resistor will be lower

[KLund1]

Thanks for the replies!

I pretty much get the notes above.

I rummaged around in the garage and found a stash of NOS red 5MM LEDs (there was label on the baggy). I attached one to the MB power LED leads and it works, but it get very hot. After 3 minutes I can't touch it. I wired up one of the other original 1200 LEDs and it works and is just a tad brighter but is not hot at all after the same 3 minutes.

So I am pretty sure there must be a difference in LED values.

SO what LED's do I need to buy to get proper replacements?

[TGB1718]

Any LED will do, all you need to know is what is the ideal forward current and it's voltage drop, the resistor

can be calculated from that, so it shouldn't get hot

[KLund1]

Thanks,

  I do not know that forward current, voltage drop is, or how to calc, or read a resistor.

I need a little hand holding on this.

[+bob1200xl]

Try Jameco. They have LEDs (LTL307E and 333973) that may work. They also have a bag of 200 LEDs for $7. Probably many will work for you.

 

Bob

 

 

[KLund1]

Thanks Bob1200XL. Those little PCB's are terrible. I already lifted one via, but easy to run a wire.