TS1000 with no image :_(

[bola_dor]

Hi, I have e this really good Sahpe TS1000 iss3.. .in fact it is an argentinian assembled and rebranded as CZ1000.. I think the only differences are the "CZERWENY CZ1000" sticker covering the original Timex Sinclair TZ1000 .. the sticker is missing anyway. And that they are 50Hz video output..
Thing is it has no video output at all.. video is not moded.. I tried two different TV set wit manual air antena setup using the original cable that I have from another Zeddy... I can see some change in the noise signal when I turn it on but I can't get even a white screen..
I've changed the 7850 as it was giving almost 0V and the input tension dropped below 4v using an original CZ500 PSU.. (14.5v unloaded ) ..
Now I check +5.4 v that replicates over all 4 ICs VCC..
Z80 and ULA were ruled out as I exchanged them with the ones of a good working another CZ1000 .. and counter checked them with the working machine..
Also tried with known working rampack (so Z80, ULA and ram are OK...
One thing I've noticed is that the heat sink of the new 7805 regulator is extremely hot.. you can't even touch it.. but tension seems to be OK (well input only drops to about 12v).. perhaps there is something shorting?
I don't leave it on for much time just in case.
I am aware that the RF modulator may not be working but the idea is to keep it original.. as the board, case, keyboard are in really good shape (only rubber feet are missing) .. and I like to see the bars when loading
What should I test?
I don't have an oscilloscope, I may get access to one.. but need to know what to look for..
Is there a simple and easily reversible video mod to do just to make the diagnostic process easier?
Thanks!!!

[Lardo Boffin]

I bought a ZX8-CCB from Sell My Retro and put it in a small project box along with an RF socket and three flying leads (to connect to the ULA pins). That works well.

[bola_dor]

I bought a ZX8-CCB from Sell My Retro and put it in a small project box along with an RF socket and three flying leads (to connect to the ULA pins). That works well.

I see... good Idea thank you..
I think it can be clamped to the RF leads and GND elsewere..

[Lardo Boffin]

I bought a ZX8-CCB from Sell My Retro and put it in a small project box along with an RF socket and three flying leads (to connect to the ULA pins). That works well.

I see... good Idea thank you..
I think it can be clamped to the RF leads and GND elsewere..

Yes you can do that - I use this quite a lot so wanted to box it to avoid clumsiness issues!

[bola_dor]

Yes you can do that - I use this quite a lot so wanted to box it to avoid clumsiness issues!

So. What do you think may be wrong with mine? I hope is not the rom
Thanks

[bola_dor]

Waaa
I had no luck at all with the video mod output.. no video signal..
I will re check ULA and Z80 with my other known working machine. Just in case. But only leaving something to be wrong at ROM or at the board itself.. wich I don't know how to test or work around so I am asking for help now.. please..
Thanks

[bola_dor]

Well.. resuming
I rechecked Z80 and ULA and they are are good.
All 4 ICs have good VCC and GND..
I tested video output directly from ULA pin 16 using a transistor/resistor mod and have no signal ..(I counter checked it with a good working identical machine and the same LCD TV) ..
I don't visually find anything wrong at the board..
When I received it 7805 was not working..
I changed it and have good 5.4 v output but I think heatsink is getting too hot.. really hot
Now I am stuck..
Have in mind that this being an argentinian version is 50Hz (PAL-N).

[1024MAK]

My test set-up is shown in this post. Also if you don’t want to buy a ZX8-CCB, have a look at the link in my signature below.

Mark

[1024MAK]

5.4V on the +5V rail is a bit high. The +5V rail should be +/-5%, so between 4.75V and 5.25V.

Can you visually inspect the 0V/GND tracks between the +9V input socket and the 7805 voltage regulator. Also (with the power off) test the resistance between the centre pin of the 7805 and the 0V/GND connection on the +9V input socket. It should be zero ohms. The heatsinks on the 7805 do run very hot, is this one running hotter than on your other ZX81/TS1000/etc computers? And is the 7805 and the heatsink well connected thermally, including a thin smear of heatsink compound/silicone/heatsink grease (plus many other names.... )?

Using a digital multimeter, what voltage do you get on ULA pin 16?

Do you own a logic probe? If no, are you up to building a simple one from three 2N3904 NPN (or indeed any reasonable NPN signal) transistors, some resistors and a green and a red LED?

Mark

[bola_dor]

My test set-up is shown in this post. Also if you don’t want to buy a ZX8-CCB, have a look at the link in my signature below.

Mark

I did something cheaper with the transistor/resistor mod.. I've got a badly brighter image with my working CZ but is good enough for the diagnosis.. you can see the crocodiles leads in a previous picture..
I have one of your buffer amplifier working inside the modulator of that working computer.
Good image BTW !.

5.4V on the +5V rail is a bit high. The +5V rail should be +/-5%, so between 4.75V and 5.25V.

Can you visually inspect the 0V/GND tracks between the +9V input socket and the 7805 voltage regulator. Also (with the power off) test the resistance between the centre pin of the 7805 and the 0V/GND connection on the +9V input socket. It should be zero ohms. The heatsinks on the 7805 do run very hot, is this one running hotter than on your other ZX81/TS1000/etc computers? And is the 7805 and the heatsink well connected thermally, including a thin smear of heatsink compound/silicone/heatsink grease (plus many other names.... )?

Using a digital multimeter, what voltage do you get on ULA pin 16?

Do you own a logic probe? If no, are you up to building a simple one from three 2N3904 NPN (or indeed any reasonable NPN signal) transistors, some resistors and a green and a red LED?

Mark

Visually I only see some brownish substance smeared over the soldering of the channel switch near the 7805.. may be flux? Related to the high temperature?

Of these the center point and the one near the regulator are soldered together and has continuitywith the 5v 8705 output lead.. is this normal ?

Resistance between plug GND and 7805 center pin is O ohm ..
Heat sink is tighten.. I doesn't have any grease but is getting hot so there is heat transfer.. now I have it open I'll add some just in case.. I don't think they used any 35years ago

ULA pin 16 is 3.10v

I don't have a logic probe .. electronics shops are closed at my town due to COVID-19 quarantine
But I may guet one borrowed during the week..