TG16: Total capacitor replacement chart + mods

[Freezer]

Like most people on this forum I love retro video gaming.  But growing up I never knew anyone with a TG16.  So about a year ago I decided to pick one up off eBay.  Given that the system is 20+ years old, I decided to replace all the system capacitors as well as add some nice mods to the system, and I documented the whole process.

Before you can do anything to the TG16, you need to open it up which requires a special tool.  You need what's commonly called "4.5mm security bit" easily found on eBay.  Although the technical name is "4.6 line head screw."  I ordered mine from ifixit.com.  Once the system is open, you'll notice the metal RF shielding is soldered onto the circuit board, both top and bottom.  Removing this isn't too difficult, it just requires a soldering iron, lots of solder wick, and some patience.  After you remove the RF shielding here's what the circuit board looks like, with the 16 electrolytic capacitors marked.


A lot of people "recap" electronics, but not everyone understands why.  The electrolytic capacitor is like a battery in that it holds a small electrical charge for later use, but over time it becomes less efficient.  Several factors cause a cap to go bad; age, exposure to heat, and initial quality are the biggest.  Capacitors are rated in farads, which is a measure of how much electricity the cap can hold.  A good multimeter can measure this value for a cap.  But it turns out, capacitance is not the best measure of a cap, equivalent series resistance (ESR) is.  ESR is a measure of how freely the cap releases the charge stored within - a low ESR is better.  As the cap ages the ESR value rises which eventually will lead to the device no longer functioning.  That's why replacing caps is usually a good idea on older electronics.  Measuring ESR on caps requires a special meter.

Here is a table of all 16 caps in the TG16.  The first column is the location on the circuit board.  The second is the rating of the cap.  The next two columns are the capacitance and ESR of the original caps in the TG16.  And the last two columns are the capacitance and ESR of the new replacement caps.


When you look at this data, you'll notice the existing and new capacitance columns are very close to the actual rating.  This is why you cannot use capacitance as a measure of how good or bad a cap really is.  You'll also notice that in almost every case the ESR of the new cap is half to a third of the old value.  The only exception is the 10uf/16V caps.  I was shocked to see that 20 year old caps had a lower ESR value than a brand new top quality brand cap.  When NEC manufactured the TG16s they must have used an exceptional batch of 10uf/16V caps.  Determining a bad cap using the ESR value is not as easy as "higher than X is a bad cap."  There are charts you use, you have to look up both the capacitance and the voltage to get a range of good ESR values.  Looking at the ESR values from the old caps, they were by no means "bad" caps.  They still had lots of good life in them.  So recapping the system wasn't necessary, but it will definitely increase the longevity of this particular system.  As for replacement caps, I used Panasonic brand FC series capacitors ordered from digikey.com.  These are widely regarded as one of the best caps for this type of work.  If you recap a system with el cheapo caps from Radio Shack, you're not doing yourself a favor.  In the short run the new caps will be better.  But these cheap caps will go bad much quicker than the caps NEC used originally.

In addition to recapping the main system, I also recapped two controllers and a TurboTap.  Each controller as well as the TurboTap contained a single 10uf/35V cap.  As with the main system I measured the capacitance and ESR of both the old and new caps.  I got similar results as before, capacitance was fine both new and old, and the ESR of the new was less than half that of the original.





In the next post I'll cover the mods I did to the system.

[Freezer]

When I first got this TG16 I connected it to my TV using the RF connector on the side.  Clearly time had not been good to this system as the quality of the RF signal was horrible!  I didn't get a picture of the RF signal, but it was very snowy.  Clearly an audio/video mod was in order.  I decided to go with the standard composite video mod you see so many others do, but I did add a little twist of my own.  I didn't like the idea of drilling three holes in the case for the new connectors, so I found a way to mount the connectors without modifying the case.

The first step is to tap the video and audio signals from the back connector.  This picture shows the TG16 rear connector.


From column 1 we want "SNDR" and "SNDL" for right and left audio.  And from column 22 we want "Vid" for the composite video.  Here's a picture with the wires attached.  I soldered onto the bottom side of the board then fed them through the holes to the top side.  The orange and orange/white stripe are for audio, and the green is for the video.  The other wires were for other mods (more details later on).


As for a mounting location, I decided to remove the RF unit and use the existing holes in the side of the TG16.  Removing the RF unit is not easy.  For me to get it off I had to use a good soldering iron, solder wick, a special low temperature solder called ChipQuik, and patience.  Here's what it looks like with the RF unit removed.


Next I took a video connector (digikey part number CP-1403-ND).  I bent the front center pin aft, and I bent one side pin out flat.  Lastly I bent the video pin straight back.  When I was done the connector looked like this.


On the TG16 motherboard, I scraped some of the solder mask off where I removed the RF unit from.


Now I can place the connector onto the motherboard and solder it up.  One leg of the connector goes through the existing hole, plus the two bent pins can be soldered onto where I removed the solder mask on the circuit board.  This gives me 3 solid solder points so I doubt this connector will ever break off.


To mount the audio connector, I first needed to raise the connector up.  If I mounted it flush on the board it did not line up with the existing hole in the side of the case.  I found a hex nut that was just the perfect thickness.  I used epoxy to attach the nut to the board.


Next I used epoxy to attach the stereo audio connector (CP1-3513-ND).  I soldered up the audio and video cables.  For the video cable I soldered a 220uF/16V bi-polar cap inline, and for the audio I soldered a 10uF/16V bi-polar cap inline.  Lastly, I soldered the ground connector onto the motherboard.


When the system is put back together, this is what it looks like from the outside.  I think it has a very clean and professional appearance.


But more importantly, what does the video quality look like?  It's pretty darn sharp, especially compared to the original RF.  This picture doesn't do it justice, I was having a hard time getting good pictures of the TV screen.  But the image is sharp and crisp.

[Freezer]

The next mod I added to the system was a reset switch.  I was shocked to discover the TG16 does not have a reset switch, so I added one.  Adding a reset switch is fairly easy, all you need is the switch and two pieces of wire.  Again, here's the pinout of the back connector of the TG16.


In column 22 is a "/RST" switch.  We need to solder one wire onto this point.  The second wire gets soldered onto any ground potential point in the system.  This can be any of the large copper traces around the edge.  You connect these two wires to your switch - but you can't use any old switch.  You need what's called an "off-mom" switch.  This means the switch is off by default, but momentarily the switch is on while you press it.  But as soon as you let go, the switch goes back to off.  I used Digikey part number 509PB-ND.

Unfortunately mounting the switch required me to drill a small hole in the side of the case.  The switch works as you'd expect, press the switch and the system resets.  Here's a picture of the final product.

[Freezer]

The final mod was a power LED.  Again, I was shocked to discover the TG16 does not have a power light.  I've seen a lot of power light mods on the TG16, but the one I liked the most was one that illuminated the logo from the backside.  Since the logo has color in it, the best would be a white LED mounted behind it.

For this mod we need 1) a power source, 2) the LED, 3) a resistor, and 4) some wires.  Most LEDs take between 2 and 3.5 volts to light up, so we need to find a power source that is at least a volt or two above that.  Fortunately the TG16 has a 5 volt regulator (highlighted below).


I turned the system on and used my multimeter identify the 5V and ground pins.  I then soldered a wire onto each.  Here's a closeup of the voltage regulator after attaching the wires.


Next you need to solder the LED and resistor onto these wires to make one big loop (don't forget about LED polarity).  It is true the LED will run off of 5V without the resistor, so why add the resistor?  If you run an LED off of more volts than it was designed for, the LED will 1) generate more heat, 2) burn out much quicker, and 3) may even shine at a different color.  But what value resistor do we need?

To calculate the resistor value we need 3 pieces of info.  First we need to know the total volts being used to power the LED (let's call it Vt).  Second we need to know the voltage of the LED, usually called the Forward Voltage (let's call it Vf).  And finally we need to know the current in amps of the LED (let's call it I).  Using my multimeter I tested the 5 volt regulator and got a value of 5.03V, so this is my Vt value.  For my LED, I chose Digikey part number 1080-1006-ND.  According to the datasheet on this LED, it has a forward voltage of 3.2 (Vf) and a current of 20 milliamps (I).

Our total voltage is 5.03, but we only want 3.2 for the LED,   So we need to "burn off" 1.83V in the resistor (let's call that Vr).  We only need one formula, V=IR (volts equal amps * resistance).  Vr = I * R.  We know Vr and I, so the formula becomes 1.83 = .02 * R.  When you divide that out you end up with 91.5 ohms.  So you need to use a resistor close to that value.  I used a 91 ohm resistor.

Next solder it all up.  Be sure and cover the exposed LED and resistor leads with heat shrink or electrical tape to prevent shorts.  I then taped the LED onto the top of the metal RF shield around the circuit board.

The final step is to enlarge the hole for the light to illuminate the underside of the logo.  If you use a razor blade you can very easily remove the TG16 logo.  I then used both a Dremel and razor blades to cut a square hole in the case.  Be sure to leave a lip around the opening so you can glue the logo back down.  Here is a picture of the opening.  Notice the LED inside the hole.


The last thing to do is glue the logo back down.  It looks pretty cool when you turn the system on.

[Lost Monkey]

Nice work! - however the reset switch is a little redundant, as there is a nice reset switch built in to the controller.

Thanks for sharing!

[Game-Tech.US]

Is this table messed up? It seems to go wrong on line c136...

[Freezer]

Is this table messed up? It seems to go wrong on line c136...

Thanks for pointing that out.  I corrected the image.

[Lost Monkey]

- Just wanted to commend you on your pictures as well - they are fantastic!

[ProfessorProfessorson]

Lots of great work there. You really went the extra mile, and the info you provided is really nice.

[thesteve]

well done.
another factor in cap replacement is voltage rating and type.
using a higher voltage cap will improve its longevity.
using ceramic, film or tantalum caps can make it infinite.

[Necromancer]

Thanks for sharing your hard work and nice pictures.  I'm too dumb to make heads or tails of 'em, but I love seeing guys dedicated to preserving our beloved Turbobs.

[HercTNT]

Welcome freezer, Great stuff! really liked the lighted logo.

[vestcoat]

Very nice, Freezer. Thanks for sharing (although I shudder at the thought of eventually replacing capacitors in every controller and piece of hardware I own).

[thesteve]

as he pointed out, the caps were still good

[Freezer]

I forgot to mention, even though the caps didn't need replacing in this system, I did it anyway for the sheer enjoyment.  To me I enjoy repairing and modding old systems just as much as playing them.  This was my third video game console; I've previously worked on a Sega Genesis model 1 and model 2.  Up next is a Sega CDX (all-in-one Sega Genesis and Sega CD).