My old neighbour years ago was having a garage clear out. He knew I was into electronics and stuff and said he was throwing out an old black and white portable TV. It was a “Maxim Tv Radio Model Mx11-06” and looked ‘interesting’

Supplies

Step 1:

Works off a bunch of C cell batteries or a 12V supply. It was cute, and the radio worked surprisingly well. The issue of course is like most of these sorts of TVs there was only a UHF antenna connection, no other video inputs. That limits its use massively, since analogue TV has not been broadcast for years. There are many old computers knocking around that do still output a UHF signal that this could pick up, however.

Tests of this using my Oric and ZX81 worked… But the picture quality was terrible. REALLY terrible. In this set, there are no presets for the tuning, it is all manual. In fact, that works quite well for old computers are they are always a little different between machines. In and around channel 36… Despite all the fiddling, however, the picture was never good enough to use.

That got to me to wonder how easy it would be to convert this little thing to a composite video input? Despite the age and the lack of colour, it was actually one of the later devices on the market. The component count is greatly reduced over older devices. By this time, a lot of the electronics had become integrated, resulting in fewer components and some larger ICs.

Step 2: The Main IC

Opening up the case revealed a highly integrated component called the CD5151CP

Step 3: Chip Pinout

It is not easy to find details about this chip, but I have compiled some stuff, from Chinese and Greek documentation.

Step 4: Detailed Pin Description

Here is a table showing the pinout functions

Step 5: The Important Pin

On the underside of the board you can see the soldered pins.

Pin 5 is marked with a black marker pen. That is ‘Video Output’ and is the pin of interest here. The IC takes in the Intermediate Frequency Video input (pin 28 and 1) from the UHV/VHF tuner. Processes this and outputs the sync signals to drive the scan coils. It also handles signal gain and amplification. The video signal is then pushed out of pin 5

Step 6: Test Equipment

I find the following bit of kit really useful when testing video/TV equipment.

It is a battery operated video game that outputs composite video and RCA audio. Very useful. It can be used to quickly and safely push composite video signals into equipment to test them. Being battery operated, it is bell behaved. At the time of testing it was actually misbehaving badly as I didn’t realize that the batteries were failing.

Step 7: Initial Test

Hooking this up and attaching video shield on the games’ machine to ground on the power input, then the video signal to a probe I was able to change the screen output.

A horrible signal, but there it obviously something there! RESULT!

Step 8: Improved Signal

Some surgery is required to cut the output of the IC so that is no longer pushes the UHF signal into the circuit.

You can see the solder blob that was from the factory. I suspect this was there for a future expansion of this device to take an external signal. On the right is the removed solder from pin 5. It came away really easily.

The yellow cable is now the video input signal that was used for testing. So with that in place, the picture looks much better.