Kenwood TS-2000 Backlight LED Retrofit - Page 1
Forum section: electronics / rf-microwave

author: xrunner
author_rank: Super Contributor
timestamp: October 01, 2018, 10:30:10 pm
content: This has been done before, but I'm going to document it here on this forum with some additional pics. My friend has two Kenwood TS-2000s and they both have back light problems. I'm replacing the bulbs with LEDs on both of them.I removed the radio top and bottom covers, all knobs on the front, the nut holding the friction assembly of the knob, four side screws that hold the front panel on, and unclipped the plastic tabs and removed the plastic front. Also remove two connectors and a white ribbon cable to get the front electronics assembly off. Then take off the four screws holding the display board and remove the white ribbon cable going to that.The original backlights are 5.5v bulbs - six total, with three pairs, each pair wired in series - see attached schematic snippet. The lamps are driven by a dimming circuit with four levels. Obviously if one lamp fails in each pair that pair will not light at all. This radio had no lights working. I unsoldered all the bulbs and found that five of the six were bad.Tomorrow I need to remove three 5.6 ohm SMD resistors and replace with 150 ohm 0.25 W resistors for the proper current drive to the LEDs. The 3mm LEDs are on order and will be here shortly. The person is slightly colorblind and we looked at some different colors of LEDs lit up, but in the end he decided to go with something that matched the original looking color (as I see it) which is an amber/yellowish tint even though it doesn't look like that to him, in case he ever wants to sell them.That's it for today.

author: Wirehead
author_rank: Regular Contributor
timestamp: October 02, 2018, 05:05:54 am
content: Wow, didn't knew they used bulbs. For a product released in 2000; that's old-school..

author: German_EE
author_rank: Super Contributor
timestamp: October 02, 2018, 10:49:40 am
content: Whilst you have the rig open please check for bad electrolytic capacitors. If you find even one you will have the owner's eternal gratitude as they make a horrible mess when they die that eats PCB traces.

author: xrunner
author_rank: Super Contributor
timestamp: October 02, 2018, 02:00:47 pm
content: Quote from: German_EE on October 02, 2018, 10:49:40 amYep, will inspect the whole rig. The ref. osc is off also (15.6 MHz). Currentl this results in an error of about 1.2kHz on 2m and over 120 Hz on 20m. That doesn't seem like much but for his friends who have very new transceivers with accurate references it's enough on HF for them to tell him he's off frequency. He wants that to stop.Quote from: Wirehead on October 02, 2018, 05:05:54 amSeems like they could have used LEDs all around the display since LEDs are used all over the rest of the front panel for status indications. I can't explain why they did it. Maybe the lead designer of that board was old school.So I did get the smd resistors removed and the 150 ohm 1/4 W resistors installed this morning. Now waiting on the mail lady.Note: Some of these steps/pics may seem simple and obvious to experienced readers but are here for anyone out there who is not confident they want to attempt this and are not sure what these mods look like from step to step, so hopefully will make it clearer to them.

author: xrunner
author_rank: Super Contributor
timestamp: October 02, 2018, 11:21:14 pm
content: Mail came - did a quick test with two LEDs wired up off the PCB and just poked in the holes. Looks pretty good so will proceed on ...

author: xrunner
author_rank: Super Contributor
timestamp: October 03, 2018, 01:59:04 pm
content: Couple of pics showing the LEDs before and after installation.I got all the parts installed and it looks gorgeous, but I do not like the resistor values (150 ohms) that were suggested by other sites regarding this mod. While on and with Max brightness level selected by the menu (which allows 9.5 V to the current limiting resistor) I'm getting (by calculation) 36 mA thru the LEDs (both LEDs together are dropping 4.1V). According to my calculations I need resistors of ~270 ohms for a 20 mA max current, so I'm going to swap out the resistors and re-test.

author: German_EE
author_rank: Super Contributor
timestamp: October 03, 2018, 06:21:00 pm
content: Next time run some sandpaper over the LEDs before you put them in, it helps prevent hotspots as an LED is more of a point source than a bulb

author: xrunner
author_rank: Super Contributor
timestamp: October 03, 2018, 10:54:11 pm
content: Quote from: German_EE on October 03, 2018, 06:21:00 pmYea I know about that trick because I do a lot of modelling (model railroad). These are already diffuse and I tried positioning them a little in and out, and a little sanding but it didn't make a real difference. It's really not that bad at all. It's funny but looking at it with a camera makes the LED area appear way more bright than it does to the eye. It's about the same in real life as many pictures of the original lighting you can find in pics of this rig - you can see the areas where the lamps were. But with the cover on it's really a nice look.I did get to the cal. I included two pics that indicate where to find the ref. osc. on the bottom of the radio - follow the pointer. Before we were off by ~+1.1 kHz on the 2m band, and now off by ~+16 Hz

author: Wirehead
author_rank: Regular Contributor
timestamp: October 04, 2018, 06:50:33 am
content: Quote from: xrunner on October 03, 2018, 10:54:11 pmYou could stick some vellum paper in front of the LED as well. Marantz used to do that for their receivers/amplifiers tuning scale. Layer for more diffuse effect/softer light.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: October 04, 2018, 09:12:40 am
content: Thanks for the report!So, thinking about to change to leds on my TS2000x; I guess, I'd take smd leds, since they have wider aperture angle than the classical 5mm leds

author: xrunner
author_rank: Super Contributor
timestamp: October 04, 2018, 12:26:05 pm
content: Quote from: HB9EVI on October 04, 2018, 09:12:40 amBest thing is to experiment if you so desire. The original lamps go into holes drilled into the plastic. Pull the board off and make a test assembly with your LED. Solder the wires to it and power it. Stick it into the hole and see how it looks. Try different kinds until you are satisfied. The LEDs I used were 3mm diffused lens. I've got the front cover back on this one and it looks really good. It's not that big a deal, but satisfy yourself as you wish.I think white LEDs would have been a good choice too. Oh yea, just remember to check the voltage drop for the particular color you choose. The supply to each pair of LEDs is ~9.5V so you might want to calculate the required resistor to use. The recommended resistor in other examples of this mod out there is 150 ohms, but for the max voltage from the dimming circuit that is too low a value. I had to up it to 270 ohms. The dimming circuit has five steps including 0v.I checked the power on all bands on this one and it looks good, so I think I'll button it up and tell the owner it's done. Then he can bring me his other one and I'll do it all over again.

author: xrunner
author_rank: Super Contributor
timestamp: October 06, 2018, 11:59:19 am
content: Just a follow up pic. I had removed the keypads and washed the front faceplate in warm soapy water, cleaned the keypads with a spray cleaner, put all the knobs in an ultrasonic cleaner, and restored the rubber of the tuning knob.Next week he's bringing me his other TS-2000. I'm going to set them on top of each other and take comparison pics since the other one still has the original bulbs, then do the same thing to the other one.