NEWBIE - Composite Mod planned, and related question

[USAJoe]

If so, I assume that I can connect the brown wire to what I thought was the bare wire video feed?

[1024MAK]

I did check for continuity at the yellow end of the diode to pin 16. It has continuity. Is that where I would need to connect video to the ZX8-CCB?

That’s the point that I would recommend you try first, yes.

If so, I assume that I can connect the brown wire to what I thought was the bare wire video feed?

No. The brown wire (video output) goes to the centre pin of the RCA/phono connector inside the modulator.

This is a photo of a U.K./European modulator, but you can see the brown wire connecting to the pin of the RCA/phono connector.

ZX8-CCB inside the modulator

3A292132-E22E-4B00-B707-9FF176CFC992.jpeg (57.94 KiB) Viewed 1899 times

You may have to disconnect any existing component leads from this point. Let me check my modulator, and I’ll get back to you later today.

Mark

[Lardo Boffin]

Heres an issue three install I did recently:

Its on the underside of the board, directly below the modulator.

The brown wire goes round to the modulator output and I disconnect all other wires going into the modulator.

I just desolder the extra black wire that is not used.

Yellow could go directly to pin 16 of the ULA but the pin I use is closer so it looks a bit neater.

Caveat - this is a UK board. I have not done a USA board.

[USAJoe]

Mark, thank you very much for your replies and patience with me. I greatly appreciate the information you have provided. I still plan to try test clip connections first for testing like you did (assuming I can do it without some required soldering).

Lardo, thank you also for sharing the information and photo!

Hopefully my next post in this thread is me expressing success!

Joe

[1024MAK]

Sorry, did not find time to do all the checks on the modulator today that I wanted to do. Hopefully will get to it tomorrow.

However, there is a low resistance connection between the centre pin of the RCA/phono connector and 0V/ground. So it looks like the components that connect to the centre pin need to be disconnected.

Mark

[USAJoe]

No need to apologize to me. I'm in no hurry. Thank you.

I'll have to like at my system to see what you mean. I'm curious as to why the guy in the YouTube video did so many configurations that worked, but never disconnected anything.

Joe

[1024MAK]

Okay, my opinion is that the components connected to the centre pin of the RCA/phono connector in the modulator need disconnecting.

The two different modulators (UM1082 LA2/3 and UM1233 E36) are completely different, using different circuitry.

The UM1233 E36 uses a 47Ω resistor to feed the UHF signal to the RCA/phono connector, so although far from ideal, this is enough that the composite video is not shorted out.

Unfortunately with the UM1082 LA2/3 modulator, it’s an entirely different situation. The components connected to the centre pin of the RCA/phono connector will short out the composite video signal, hence they need disconnecting.

Mark

[USAJoe]

Thank you, Mark. It sounds like I would be better off just abandoning the idea of retaining the RF capability, which I’m okay with doing.

I’ll look at things better in two days. I’ll be spreading my parents ashes in the Pacific tomorrow, then make the long drive home at night. This has been delayed due to COVID.

In practicing my soldering, I’m concerned about the close proximity of the solder pads (wire connecting points) on the ZX8-CCB and ending up with a solder bridge. So much more practice is required. Desoldering practice too!

Joe

[1024MAK]

Desoldering is harder than soldering.

The ZX81/TS1000 boards and modulators use a lead and tin based solder. I don’t know what the ZX8-CCB boards use (likely they use lead free solder for the preassembled components).

You are not supposed to mix lead and lead free solders, as doing so contaminates the solder and creates a third different alloy with undesirable properties.

As I mostly work on old electronics, I only use lead based solder.

And yes, with soldering and desoldering, practice, as in lots, on scrap boards after watching either someone in person or videos of people soldering.

Mark

[USAJoe]

I've been communicating via email with Stewart and zebrasystems.com (U.S. based) who sold me my ZX8-CCB. He provides online technical support, and even is willing to take a phone call at reasonable times of the day.

With his help. I have a final design for installation. I even have a plan for using the RF modulator housing and the existing RCA jack. He also provided some recommendations on removing the RF modulator housing from the PCB, and removing the RF board from the housing.

So have I installed it yet? No. I've run out of time since I have to prepare the house for hosting a combination of three birthdays for a party this coming weekend. Then I leave for Hawaii on Monday for 11 days (I can't really call it a vacation since I'm retired).

So it will have to wait. My brother in-law will help me with the de-soldering and soldering. He's highly skilled at it. I know how to burn my fingers.

Thank you everyone for your help. I'll report back after the completion of the mod project.

Joe