NEWBIE - Composite Mod planned, and related question

[USAJoe]

Well, I'm back from vacation and all of the family obligations.

Before I go into detail, I need to ask if the TS-1000 will boot without the keyboard installed? Keep this in mind for when I ask how to reinstall the keyboard (yes, it's an issue)

Today, I did this:
1) Removed the RF modulator by desoldering it from the main board. Then I did the same to the modulator internals, and cut the three solid wires that were going into the modulator. I left a long piece of the center wire for the RCA jack available for connection from the ZX8-CCB.

2) I soldered the four wires (video out, video in, power, and 0V) to the ZX8-CCB. I'm not using the ground by the video out ground since I did not install a new RCA jack. I had verified several times which wires go where on the ZX8-CCB before soldering, and the sources for the video, power, and ground on the main board. I soldered the video out wire to the center pin on the RCA jack. I checked continuity on all of the connections by touching the solder only, and the RCA center wire. I also inspected for solder bridges.

3) Without the main board reinstalled in the chassis, and without the keyboard connected, I connected the wires coming from the ZX8-CCB to their destinations on the main board using jumper connections and verified continuity for all of the connections.

4) At this point, the RF modulator chassis is not reinstalled on the main board. And nothing is soldered to the main board as of yet.

5) I connected a composite cable from the RCA jack (three different cables tried) and to the composite on the TV (which I use for my Commodore computers).

6) I powered everything on, and I get "no signal" on the TV.

7) I verified power to the computer, and it's fine. I even grounded the modulator chassis since it's not connected to the main board at this point. No difference. I checked continuity from the pins on the ULA to their respective connections on the ZX8-CCB, and they are fine.

Any ideas as to what to check next?

Thank you!

Joe

[TMAOne]

Yes, a ZX81 or Timex-Sinclair 1000 will happily boot to a K cursor with no keyboard attached.

In my experience, some modern TV's do not like the composite signal coming out of a Sinclair. I don't know exactly why. I only know that I have one TV that refuses to acknowledge that any signal is there, and frustratingly displays its default "user friendly" blackened screen instead. Try other TV(s) if you have any available.

[USAJoe]

I can give it a try. The one I use with my Commodore computers is from 2011. I have two other monitor/TV's from 2009 that I'll try out.

Thank you!

Joe

Oh, and here's some pictures from my soldering:

[mikeh_nz]

Maybe some pictures of where you connected it to on the motherboard?

With no power, It sounds like you’ve confirmed continuity between

• pin 16 of the ula and the yellow wire
• 5v (so say pin 40 of the ula) and the red wire
• GND (say pin 34 of the ula) and the black(or blue?) wire
• The outside of the rca connector and GND (say black or blue wire)

And confirmed that there isn’t continuity between red & yellow, red & black, yellow & black, white & black wires

[Edit: Ignore the next question. I see from an earlier picture you posted that R30 is present]
Can you confirm that resistor R30 is present on the board? (Ie the blue resistor south of the ula in the attached picture)

This is how I ended up hooking it up - but there’s many ways to skin a cat…

And with power, carefully confirm that the voltage between

• red and black is about 5v (careful to only touch what you want to measure)
• yellow and black is something like 4.5V

I agree that trying on different tv is a good next step. Namely confirm whether the other Tv appears to be painting a white screen, black screen, or no signal.


Other options

• try a complete readjustment of the zx8-ccb. (Adjustment section of this). Namely R2 fully clockwise to force a white screen output. Then play around with R1 until white picture comes. Then R2 to get the “K” to appear and look good.
• borrow/buy an oscilloscope and connect to the yellow wire to confirm that you’re getting a signal coming in. And then also to the white wire to see what’s going out.

Hope this helps
Mike

[USAJoe]

I did find an issue where the 0V wire did not have continuity between the connection point on the board (bare wire closest to the ULA) and pin 34 of the ULA. So I moved the alligator clip to the pad where the modulator mounts and received continuity there and at the 0V on the ZX8-CCB. I tried booting after that, and got the "no signal" message again.

As I checked for other potential continuity issues, I discovered that where I had the 0V wire connecting to a bare wire (closest to the ULA) from the board before is actually hot. I checked for continuity between pin 40 and each bare wire (middle and closest to the ULA), and it was there. I could have sworn I checked everything multiple times before I made connections. Then I checked the middle bare wire and the bare wire closest to the ULA for continuity back to the voltage regulator, and both are hot.

I made the corrections, and there's no difference. I get the "no signal" message. To top it off, something smells hot.

So now I'm worried that I fried my ZX8-CCB, if not more on the main board.

Here's photos of my configuration. The red connector is connected to the center bare wire. The yellow connector is connected to the yellow side of the diode near the D9 designation.

Stupidity is free. Paying to fix it isn't.

[mikeh_nz]

I believe think the middle bare wire is 5v (USA2)
The bare wire closet to the ula (USA1) is connected to the channel 2/3 switch and depending on the switch gets 0v or 5V

I ended up connecting to the middle wire (USA2) for 5v and connected the yellow wire to UK2 (that I believe is a direct connection to pin 16 on the ula)

Your pictures looked alright to me. I don’t really know about where you’ve connected the yellow. But I assume there is continuity from there to both pin16 on the ula and also uk2 on the board.

It does seem like you did short GND and 5v together via the usa1 wire at one point. (You must of flipped the channel switch at some point)

Maybe double check the connections again and switch on again to see if you get your burning smell.

I’d still try on a different tv. Try the adjustment of r2 & r1 on the board.

I’d carefully measure the voltage between pin 16 and ground. But ideally I’d want to see what pin 16 looks like on an oscilloscope.

I was pretty much in the same situation as you about 3 months ago trying to figure it all out. Here’s my post - you’ll get there!

[USAJoe]

I believe think the middle bare wire is 5v (USA2)
I reconnected the red lead to this wire.

The bare wire closet to the ula (USA1) is connected to the channel 2/3 switch and depending on the switch gets 0v or 5V
I changed the switch to produce 0V and double checked with no continuity to that pin.

I ended up connecting to the middle wire (USA2) for 5v and connected the yellow wire to UK2 (that I believe is a direct connection to pin 16 on the ula)
I connected the yellow wire to UK2 after verifying that it is a direct feed from pin 16 on the ULA.

Your pictures looked alright to me. I don’t really know about where you’ve connected the yellow. But I assume there is continuity from there to both pin16 on the ula and also uk2 on the board.
I had the connector to the yellow end of the diode as recommended by someone else. Yes, it has continuity back to pin 16 of the ULA.

It does seem like you did short GND and 5v together via the usa1 wire at one point. (You must of flipped the channel switch at some point)
Yes, I apparently did.

Maybe double check the connections again and switch on again to see if you get your burning smell.
I did reconnect things correctly this time and tried again. No burning smell. But the ULA was getting very warm (not hot).

I’d still try on a different tv. Try the adjustment of r2 & r1 on the board.
I did try again on a 2007 LCD TV that I forgot I had picked up from a thrift store. Below is the intermittent picture I was getting (sometimes the picture would just be blue - I think due to using the clips). Sometimes it scrolled, sometimes it didn't. I tried adjusting R2 & R1, but it made no difference.

I’d carefully measure the voltage between pin 16 and ground. But ideally I’d want to see what pin 16 looks like on an oscilloscope.
I would love to have a steady enough hand to do take the voltage reading, but I don't trust my hands sometimes. I do have a PC based oscilloscope on my Amazon "Wish List" for upcoming Father's Day / Birthday in June (I was asked not to buy anything soon because I'm hard to buy for). But there will be a learning curve for the oscilloscope as well.
----------------

I do greatly appreciate your time and help. I did order a new ZX8-CCB since they're cheap enough. I'll probably end up buying another TS1000 as well just in case I fried this one.

Joe

[USAJoe]

One more thing. Since I changed the "channel switch" to provide 0V to the bare wire closest to the ULA, I can use that for my 0V in the future with a new ZX8-CCB, correct? And Yes, I will disable the ability for that switch to ever work again.

Joe

[mikeh_nz]

If you hardwired the switch to ground (ie desoldered the switch and joined one of the connections) you could use USA1 as your GND (I’m guessing it’s center pin to left pin - I’m guessing left is GND and right is 5V but I’m not 100% sure)

However, I think it would be easier for you to just solder the black wire to the inside of the modulator case (as it’s grounded when it’s mounted back on the motherboard.)

Or use Fr3 - pretty sure that hole is GND as well

[1024MAK]

ZX81/TS1000 Modulator PCB connections

Fr3 = 0V/GND - black wire to ZX8-CCB
Fr2/USA3 = (video) - Don’t use this signal.
UK2 = video - yellow wire to ZX8-CCB
USA2 = +5V - red wire to ZX8-CCB
Fr/UK1 = +5V
USA1 = to switch - Don’t use this signal. Slide switches are not the most reliable, and how old is this now?

As you have already tried adjusting the ZX8-CCB, it will have to be set up again.

Mark