NEWBIE - Composite Mod planned, and related question

[USAJoe]

Yes. Mine is like that. Here's a photo of the board.



Is there a resistor on my modulator that I should modify per your recommendation? I can't tell since mine doesn't look similar.

I ordered some of the clips you had in one of your previous photos. Thanks for sharing that! Those are much easier and cleaner to attach than "alligator" clips.

My ZX8-CCB board should arrive in a few days. That's fine with me. I'll be busy, I'm going to a Commodore Computer event this weekend in Burbank, CA. I call it the "Old Guys using Old Commodore Computers" event. This will be my first time attending.

The acquisition of the Sinclair 1000 is the most recent addition to my "Classic Computers" collection. I have a Commodore VIC-20, Commodore 64, Commodore 128, two Commodore 1541 floppy drives, a Commodore 1571 floppy drive, a Commodore CN2 Cassette unit, Commodore 1902 color monitor, a newly developed external SD storage device for the Commodore units, Apple IIe with Duodisk floppy unit, a single Apple floppy drive, a Apple monochrome (green) monitor, a complete Apple IIc system with a small Apple monochrome monitor, Microsoft Softcard, Applicard, several newly developed disk storage and control devices for the Apple IIe, and finally.. my Radio Shack TRS80 PC-2 with printer/cassette interface. I had to replace the gears on the printer part of the unit. Lots of time at home due to the COVID pandemic gave me the opportunity to start my collection and expand my hobby and learning activities.

Joe

[Paul]

No the US Version seems to be connected by a capacitor already. So US Versions can have the Video directly to the middle pin of the RF out without modifications.

[1024MAK]

The acquisition of the Sinclair 1000 is the most recent addition to my "Classic Computers" collection. I have a Commodore VIC-20, Commodore 64, Commodore 128, two Commodore 1541 floppy drives, a Commodore 1571 floppy drive, a Commodore CN2 Cassette unit, Commodore 1902 color monitor, a newly developed external SD storage device for the Commodore units, Apple IIe with Duodisk floppy unit, a single Apple floppy drive, a Apple monochrome (green) monitor, a complete Apple IIc system with a small Apple monochrome monitor, Microsoft Softcard, Applicard, several newly developed disk storage and control devices for the Apple IIe, and finally.. my Radio Shack TRS80 PC-2 with printer/cassette interface. I had to replace the gears on the printer part of the unit. Lots of time at home due to the COVID pandemic gave me the opportunity to start my collection and expand my hobby and learning activities.

Apple II, IIc, IIe and related computers are not particularly common in the U.K., I don’t know about elsewhere in Europe. Commodore computers, that’s another matter. They did well in the U.K. and in various other European countries. I myself have a couple of 64C machines (the later version) plus a breadbox version. I also have Commodore 128. And one working 1541 floppy drive. I think I have three datacassettes (they sometimes turn upon a bundle of other items that are not Commodore related).

Back to your TS1000 board. The circuitry should be the same as on the board that I showed a photo of, but obviously the components are arranged differently. The connections to the modulator should be the same.

Mark

[1024MAK]

No the US Version seems to be connected by a capacitor already. So US Versions can have the Video directly to the middle pin of the RF out without modifications.

In the UM1082 LA2/3 VHF modulator on my TS1000 board, the centre pin of the phono/RCA connector is linked to the PCB by a tinned copper wire. In addition, there is a coil and a ceramic capacitor wired in parallel with the other end being soldered to the corner of the metal case (which is 0V/ground), I can’t tell if the coil is wound on a former or if it’s actually a resistor that it is wound on. At least not with taking it apart. If I had to guess, I would say that it looks more like a resistor than a former, as I can just about see what looks like a band.

Mark

[USAJoe]

So I received my ZX8-CCB in the mail. Yes, I'm still learning on how to improve my soldering skills as well. Now that I have the board, I've gone back to view the YouTube video I have previously mentioned in this thread where the person in the video connects the ZX8-CCB to his Sinclair 1000 while maintaining the original RF output option as well.What I did notice is that he never uses the second ground connection near the brown wire connection point on the ZX8-CCB. He uses only the one that is close to where the video and power connections on the ZX8-CCB board are made. That puzzles me.

Meanwhile, I used my multimeter to confirm ground, power and video (at least I think it's video). To check the ground continuity, I touched the ground middle leg on the regulator (NEC 7805) and touched the housing for the modulator (as is done in the video I mentioned). Continuity was good. For the power continuity test. I touched the output leg (the one furthest from the modulator) of the regulator and the center bare wire leading from the board into the modulator. Continuity was good there was well. I did touch the other wires in this test to verify that there was only one option for it being power. For the video continuity test, and this is a source for one of my questions, I touched the RCA plug and the bare wire (closest to the ULA chip) that leads into the modulator. This too also tested good for continuity.

I've attached a photo of a proposed final connection of the ZX8-CCB wires to the Sinclair 1000. The black wire is connected to the ground leg on the regulator (I'm thinking I can use the modulator housing as well, but not sure), the red wire is connected to the bare wire that has been identified as power, the yellow wire in connected to what appears to be the video (not 100% sure if this is video in), and the brown wire connects directly to the RCA connector. As you may have noticed, I have no idea what the third bare wire (the one to the left of the red connection) is used for. I've tried to find other photos of a board that is identical to mine, but I have not been successful. So it remains a mystery to me.

Here's my questions:
(1) Am I correct in the identification of the bare wire that the yellow test lead is connected to as being the "video in" connection?
(2) Do I need to use the second ground (the one by the brown wire connection point on the ZX8-CCB)? If so, where do I connect it?
(3) Does anyone know what the unidentified third bare wire into the modulator is used for?
(4) Based on what you have read in this post, and seeing my attached photo, do my proposed connections look correct and complete (not using second ground)?

Thank you!

Joe

[USAJoe]

I don't see the attachments, so let me try it again.

[1024MAK]

Here's my questions:
(1) Am I correct in the identification of the bare wire that the yellow test lead is connected to as being the "video in" connection?

I don’t think so. What you need is the video output from the ULA. This is on pin 16. You will need to follow the PCB tracks (traces) to find a suitable point to connect it if using the clips.
You could try on the modulator connection. Does yours have the same part number as the one I posted a photo of earlier in the topic? If yes, use the wire I labelled as video input.

(2) Do I need to use the second ground (the one by the brown wire connection point on the ZX8-CCB)? If so, where do I connect it?

No. You don’t have to use both ground wires. The second one was provided for use when a separate RCA/phono socket is being used.

If not using it, tape up the end and secure it so that it can’t flap around and touch any other conductors or components.

(3) Does anyone know what the unidentified third bare wire into the modulator is used for?

It’s a switched input (either +5V/VCC or 0V/ground) to tell the modulator which TV channel to output on. But keep in mind that you may have mixed this up with the video input wire. But I can’t tell for certain, as I don’t have that PCB version.

Mark

[USAJoe]

Thank you for the prompt reply!

The cover for the modulator on my board shows "UM 1082 LA2/3". Yours is the same other than the smaller number below and the source country (mine says Philippines) . In one photo, you have my unknown care wire labeled as video. But it doesn't say input.

I traced pin 16 to a solder joint shown in the attached photo (green circle next to the yellow clip). I verified it several times with a continuity test. Does this sound odd to you?

Joe

[1024MAK]

The four digit number is the date code when it was manufactured. For example 8151 decodes as the year 1981, 51st week of the year.
The type number is the same as the one in my photo.

I cannot answer your question about pin 16 going to the solder joint you marked, as I don’t have the same board as yours. I would expect the circuitry to be similar if not the same.

Right next to your green circle is diode D9, it’s the yellow coloured component with a black ring at one end. Test ULA pin 16 to the lead of D9 that is at the opposite end to the black ring. That is the lead nearest the Mic socket.

Mark

[USAJoe]

Thank you for that information.

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?

Joe