Hitachi B&W portable TV schematic needed model K-2200 - Page 1
Forum section: electronics / projects

author: poot36
author_rank: Frequent Contributor
timestamp: September 12, 2015, 11:46:30 pm
content: I am trying to modify this portable TV to place a ATSC converter box in it. My plan is to take the original tuner out to make space and place the circuit board of the converter box in it. Both the converter box and TV run off 12V so I think it will work. Just need to know where to inject the composite and mono sound signal into the TV.

author: German_EE
author_rank: Super Contributor
timestamp: September 13, 2015, 04:12:02 pm
content: This depends on what signals out there are from your ATSC box. In Europe it's easy because we have SCART connectors and these will give you audio and video out along with mixed sync.However, a warning.Check VERY CAREFULLY that your TV set is not a live chassis, this includes looking carefully at the mains plug and what happens to the TV internal ground when that mains plug is reversed in the wall outlet.You will need to find the following points inside the TV set. As it's a black & white set I'm guessing that the board won't just be a single chip in the middle that does everything, this makes the job easier1) Audio amplifier. Trace the connection from the loudspeaker back on the PCB and you will eventually find either a pair of small power transistors or (more likely) an audio power amplifier. The datasheet for the chip will give you the input pin, feed your audio in here via a 100n mains rated capacitor.If your ATSC box has composite video out then2) Find the output of the video detector. This is after the IF strip and at the point where the signal splits into two, video and audio. In theory this signal should be DC coupled from your ATSC box but see the warning above regarding the live chassis.If your ATSC box has separate red, green and blue outputs then2a) Combine the three color signals using three 75 ohm resistors then feed into the TV after the video detector. See the above warning about the live chassis.3) If you have separate red, green and blue outputs then you may also have a sync signal, this signal should be DC coupled tgo the output of the sync separator circuit in the TV. See the above warning about the live chassis. If you DON'T have a separate sync connection then the convention is to sync on the green or the blue signal, you will need to check both lines with a scope to see if the sync pulses are present.If your ATSC box has S-Video Out then you're on your own as I have never worked with this connector.Check VERY CAREFULLY that your TV set is not a live chassis, this includes looking carefully at the mains plug and what happens to the TV internal ground when that mains plug is reversed in the wall outlet.

author: poot36
author_rank: Frequent Contributor
timestamp: September 13, 2015, 06:55:47 pm
content: The TV is a portable one with digitally controlled tuning (black bar appears as a tuning indicator on the screen). The TV runs off 12V through a transformer pack or a optional battery pack that I do not have. How would I determine if it was a hot chassis in this case? The ATSC tuner outputs composite video (yellow plug) along with stereo audio through the wight and red RCA jacks that I will have to combine for the mono speaker. I can take pictures of the TV and chassis if necessary.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 07:01:41 pm
content: 12V with separate PSU is not a worry, only if it was powered direct from the AC line, where most sets are live chassis to save cost.

author: poot36
author_rank: Frequent Contributor
timestamp: September 13, 2015, 07:25:05 pm
content: Here is some low res pics of the TV.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 14, 2015, 04:45:19 am
content: Could you find a composite LCD that fits? That would give you color and plenty of room for other stuff.

author: poot36
author_rank: Frequent Contributor
timestamp: September 14, 2015, 05:07:47 am
content: I probably could but what is the fun in that? I already have the parts (TV was under $5 at a garage sale, ATSC tuner box around $7 or so) pretty sure the LCD would cost more than that. It would also give me an excuse to try and use the what I think is a rotary encoder for the TVs electronic tuning as a input for the channel up down controls on the ATSC tuner box. I have no clue how to get the PCB out of the TV currently so I was hoping someone had the service manual that would tell me how to do that safely. This is a Canadian made (or maybe just assembled) TV as far as I can tell. I have tried emailing Hitachi for the user or service manual and I did not get a response. Got any ideas?

author: poot36
author_rank: Frequent Contributor
timestamp: September 27, 2015, 11:11:09 pm
content: Well I managed to get the whole thing apart with out damaging anything. Here are some higher resolution pictures before I totally took it apart. On the back of the tuner the outputs are labeled (from top to bottom as shown in the pics) as follows VTU, BU, AGC-U, BM, TP, Bl, IF, GND, VT-V, BH, AGC-V. There are only 2 ICs that I can see in the TV, IC301 (MSM4011RS) and IC401 (HA11229). Got any idea where the video signal would be accessible?

author: poot36
author_rank: Frequent Contributor
timestamp: September 27, 2015, 11:12:41 pm
content: Here is some more pics.

author: Gyro
author_rank: Super Contributor
timestamp: September 28, 2015, 08:46:28 am
content: Unusual looking TV, the front looks more like a piece of test gear!

author: Delta
author_rank: Super Contributor
timestamp: September 28, 2015, 12:22:53 pm
content: See if you can find a datasheet for the tuner. If not, probe it! 😀