mod plan: power LED for Duo-R

[wilykat]

PC Engine, Coregrafx, Turbografx-16 all have one thing in common: no LED at all.  CD system has drive LED but that is all.  I wanted a power on indicator.  There were 2 ways of doing it.


Easy way: adding a second LED alongside existing LED wired to 5v and ground. The only drawback is it'd mix color with drive LED.  You could change drive LED and color coordinate with a second LED to get a nice pleasing one color for drive, second color for other. But I wanted blue for power on with no drive and red for drive.  Since there's no way to combine blue with something to get solid red, the easy plan won't work.

Harder way: second LED is switched electronically so it comes on when the drive LED is not on.  I found a quick schematic that seemed to do the trick:


and my finished LED assembly:

I opted for dead bug style, with only 4 parts it wasn't worth wasting a PCB.  The LED anode and cathode lined up with collector and emitter of the transistor. Anode/collector led connected to a 1k resistor (which with 5v makes for a nice blue light that won't melt eyes like some cheap electronis LED can), emitter ad cathode side are connected to ground. The blue wire with 10k resistor inline is to go somewhere.

I'll post update when I finish, verify my idea works, and get video.

PS I did check the drive LED when I was fixing bad RAM issue (different thread) and saw the cathode is connected to ground and anode is connected to a 470 ohms resistor to a transistor, one leg to 5v and other leg probably to an IC chip for drive activity. I plan to tap onto that transistor pin.  The layout is probably the same on RX (since it's only 1 letter printing on console and a 6-button controller instead of 2 button controller as pack in) but it would likely be different on black Duo.

[wilykat]

And it works! I would have been done sooner but the bad storm chased me away for a while.

[wilykat]

oops video would help:

[bozo55]

That's pretty awesome.  It came out looking really professional.

[wilykat]

Update: https://i.imgur.com/s0FmnFD.jpg for the motherboard picture with the wiring.

Red and black are for 5v and ground. The bulge in the red heatshrink contains a 1k resistor to limit LED current and to prevent short through transistor.  The blue LED with another resistor inside heat shrink goes to R401, the side toward the front of the console.  The traces that goes to LED are: from other side of LED to anode, and the other trace that goes under the resistor is ground for cathode.  Transistor Q106 controls the LED but turning on when the CD drive is running.

Ignore the yellow wire, it was to fix a bad trace to the 128k memory chip causing SCD games to load with corrupted graphics.

The transistor I used is a generic NPN whoce collector and emitter leads are on the outside and lined up perfectly with LED leads. The middle lead is the  base.  If you used different transistor, check the pinout, for idiotic reason no one followed any rule about transistor lead arraingement so every model may be different.  Why couldn't they make all transistor have collector one side, base middle, and emitter other side?

[blueraven]

wily,

Goddamn.

This is an amazing thread, and I have to commend you for such a simple hack that updates the system and makes it more interactive during gameplay, or in my case, reminds my dumb ass to turn the system off because the Power LED is staring me in the face 

...I have been reading this thread over for the last week and have kept it open in my taskbar... I realized that I had all of the parts to make this happen, so I started to construct a prototype based on your two posts... and the picture.



The transisitor I had was very small, and on the blue wire, mirroring your blue wire, I constructed the lead, but instead of a 10K resistor, I used an 8.7K, because it was the closest Ohm rating that I had to your construction. I then lined up the two sides of the LED according to your specifications on both the electrical diagram, and added a ground wire (brown), and a power wire (orange) with another resistor (this time 2.7 or 4.3k, because it was the lowest resistance I had) running from the other side of the LED's positive leg.



This shows transistor #3  , I ended up using a total of 4 because the legs were so tiny, they would bend off or snap after being re-soldered so many times. The first three were a learning experience, to say the least, and I didn't have a nifty bezel like you posted in the previous photo.

...3 breaks, 4 hours of searching, one set of "helping hands", a headlamp, and a shot of Jim Beam later:



Here's hoping it works!! I will be installing it tomorrow after I finish the region mod...

And I will undoubtedly have a few questions!

Great thread! And thank you!!

[wilykat]

You're welcome!  Sometimes it's something very simple that is also very useful.  I am surprised no one thought of adding power LED that goes off when drive LED comes on.  LED, cheap transistors, and couple resistors have been around far longer than PC Engine has and this design is pretty simple and well known.

[blueraven]

Wily,

Yes, its an awesome design, and quite simple! A quick question...

Where does the blue wire go on a PC Engine Duo? There is a P401 on the PCE duo, but it doesn't look anything like R401 on the the Duo-R, so instead of just soldering it to a random place, I'm waiting to get a hot glue gun to secure the apparatus, and figure out where it goes.

I assume that this is the place where the CD signal comes from, that regulates the switching between the two LED's.

Any ideas? Thanks!

[wilykat]

Assuming cathode of the original LED is tied to ground, follow where anode trace goes. It should go to a resistor for current limiting, then to transistor where the CD system uses to switch LED on when it's running CD.

I tapped in the spot between that transistor and resistor.  I don't have a black Duo and I don't have a very high resolution of the mainboard (both side) to follow trace and suggest spot to tap for switching signal.

[NightWolve]

oops video would help:

I like it, nice work!