Sharing a build and install

[kdorff]

You can close this. I just wanted to share.

I ordered the PCB from your repo and installed it in my TS1000 (US version of ZX81). See https://imgur.com/gallery/2F53GVl

My thoughts, but no need to change anything.

• The position of the input/output pins nearly conflicts with the RCA jack (in the only orientation I could install the PCB). But it did work. Yay!
• I had trouble soldering the PCB to the can - getting the can to take solder. I realized LATER I needed to sand the can. I just soldered a ground wire to the bottom and brought that up (and then later sanded and soldered it to the insider of the can). My 22AWG solid core wire was a very tight fit to bring a ground from the bottom :)
• The video looks great!

My only suggestion MIGHT be to add a pin for ground, in case you don't want to solder it at the bottom to the can. But I should have realized to sand the inside of the can and it would have probably soldered just fine. And I should have used a fatter tip, maybe.

[0ddjob]

Yep, I came across the same issue with the RCA jack last night in my TS1000! In the ZX81 the RCA jack is at the other end of the modulator can so I believe this is what it was designed for.

For soldering the ground to the can you could also try using some flux paste - this helps the solder adhere to the can.

Unfortunately I need to troubleshoot mine a bit more - the modulator can is somehow ending up at around 4.5V rather than ground ... but it's good to hear some someone that it does actually work!

2022-08-15 09 29 07

Brett.

[kdorff]

I'm betting you bridged the legs on one of the transistors. Thanks for the flux paste recommendation. I have it and need to use it more.

[0ddjob]

Ah huh, thanks, will have a proper look ... the legs are quite close together, aren't they! ;) Your suggestion about an additional ground pin is good - the original strip board design has this, and this is also how I wire up the simple emitter-follower buffer I've been using before trying this out. Of course, space is already at a premium on this board. Brett.

[0ddjob]

Still not working. Made up a 2nd board - no go. I've found that there's two similar designs - the main difference being transistor - BC337 in this one and 2N2222 in the other.

[kdorff]

I've built this circuit and used it in two TS1000's. One that had a back porch (I omitted the 555) and one didn't. It worked great for both.

Check your components and solder joints is all I can think. I first ran it outside of the can, running a ground wire to a bottom pad for testing. Make sure to take the video signal from pin 16 directly or use UK2 next to the RF can (but I wouldn't use USA3).

If you have a microscope, use that to check the solder joints on the transistor. This was initially my problem.

There was, from the original RF circuitry, a coil (?) and a capacitor soldered to the RCA Jack. I removed those before doing any testing.

I found the schematic in this pdf to be helpful.