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Anyone worked with a TDA4500? Small signal combination IC for monochrome TV


taito

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I've had this project on the go for a few months. I've got a Lemair B&W 13" TV. It has no composite sync in, only and aerial port on back, or RF input. It's a cool little set and I wanted to get it going to make a mini Speed Race Deluxe or mini Sprint 2, just for fun. Or a pong project.

 

lemair.thumb.jpg.753e40b2d9e8769ba6f960b4e18d239d.jpg

 

inside.thumb.jpg.7d59bbca9d4e9f9b74ae7ff0ec73160d.jpg

 

So how do I get a picture I thought? Buy hacking the TDA4500 general purpose IC. I was off to a flying start as pin 16 is picture out, so I lifted the pin from the socket and then soldered in a video signal trace to the pcb (pin 16). I got a bit of a picture but it wouldn't stand still and is all skewed and jumpy, and just not good at all. :o

 

Anyway so obviously I need the sync. I was in a bit of a mad scientist mood, (I built a LR network that delayed the sync but I couldn't get the timing right.)

 

I had a sort of OK picture at one point, (apologies for no photos) but the vertical was out by 90 or 180 degrees, so I got a bit of the picture at the top an a bit below. I figured this had to do with the way the IC does a 90 degree phase shift, I had the signal go through the chip so it generate a sync, but by bypassing the picture signal straight to the chassis, so they were out of phase I guess. Changing value of L and R moved the picutre about a bit but I was obviously out of my deepth. sigh.

 

After looking at it again the other day and trying different things...I'm getting lazy I suppose. Just putting it out there if anyone else has hacked this IC? and would like to share. ;)

 

This is a suggested circuit from the datasheet.

 

1931012677_Screenshotfrom2019-02-14185922.thumb.png.35626476333e193be839763c5c834641.png

 

I'm thinking I can't use i.f. input because that input expects TV signal... wibbly wobbly stuff. I'm hoping just to trick the IC somehow with the right inputs outputs here and there... :)

 

I tried the aerial input to start with, but that was no good? Maybe I needed to match the impedance or something? @Kaizen? You have been busy with B&W's. Do I need a special tv set to start with?

 

UPDATE: I'm hoping to be corrected here, but I don't think it can be done with the IC. If I use a separate sync line and a separate picture line I can create a picture by inserting upstream of the IC, as mentioned, but looking at the circuit above, the timing is depended on the signal going into the IC. It can't just be free running as I'd hoped because how do you line up the H and V sync. This is done, I've found on most arcade chassis with with oscillators that can be interrupted by the sync signal, bringing them into sync, but I can't work out how to do this here. I give up! :lol

 

I suppose I could take the H sync direct from a game PCB and put it at the Horizontal output PIN 27 with a coupling capacitor of about 1uf. and do the same with the V sync, but the circuit seams to be dependent on feedback to and from the IC. So still don't know...

 

Read this on a post...https://www.eevblog.com/forum/projects/retrofitting-av-input-on-an-old-bw-tv/

 

Take an old RF modulator out of a video game console or old VHS, add power to it and feed it to the set. :o

 

Good idea but I think the picture will be like an atari 2600, with all those interference patterns.

Edited by taito
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Your TV has a UHF tuner so I would just go with one of these... I've used it for a Pong cab and it worked fine.

 

https://www.jaycar.com.au/stereo-audio-and-video-rf-modulator/p/LM3880

 

 

(Or one of these if your TV only has a VHF tuner)

https://www.wagneronline.com.au/video-to-rf-modulator-f-connector/wn-archive-2013/new-products/rf5300f-43389/967295/pd/

 

DHlkRkt.jpg

 

Edited by Kaizen
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Hey thanks @Kaizen! That is a great picture!! :) Thanks for the cool demo too!!

 

Jaycar! Who'd have thought! lol.

 

I whipped out the Atari 2600 just to check. That has a modulated signal out. Fashioned a converter because I don't have the back of the TV, and plugged it into VHF socket. Popped in Kung Fu Master. So nice. A "composite in" one of those gadgets is an elegant solution. This TV has both UHF and VHF. Thanks again!! @Kaizen.

 

converter.thumb.jpg.0d0cd3e938a2482041bfe72b01b6c210.jpg

 

kungfumaster.thumb.jpg.ce433e88d6e6639382e1924d3b92ca81.jpg

 

Case closed. :)

Edited by taito
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Jaycar generally quite expensive with their RF modulators.

 

I have one of these a fair bit cheaper.

 

Another option is to check gumtree and facebook marketplace.

 

EDIT: Ok, $40 at Jaycar not too bad.

 

Also, I was thinking you could look at modding the TV to try and inject composite video directly onto the chassis but I figure with a monochrome display you won't see a lot of difference between RF and composite, (I might be wrong, I don't have experience with B&W)

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