TS1000 with no image :_(

Discussions about Sinclair ZX80 and ZX81 Hardware
bola_dor
Posts: 138
Joined: Wed Oct 02, 2019 5:32 am

Re: TS1000 with no image :_(

Post by bola_dor »

Did the static test.
Without the ULA, Z80 pin 6 is high at 5.4v
With the wire from ULA socket pin 14 to pin 40, Z80 pin 6 is low at 0.13v..
So Tr2 is good.. :D
I wonder why ULA pin 14 gave me such a low tension..?
May be tomorrow I can get access to an oscilloscope..
What should I look for?
Perhaps the picture helps someone in the future..
Just for the curiosity, why does it has to be a solid core wire?
Thanks again!!
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20200326_012330.jpg

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Paul
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Joined: Thu May 27, 2010 8:15 am
Location: Germanys west end

Re: TS1000 with no image :_(

Post by Paul »

bola_dor wrote:
Thu Mar 26, 2020 5:35 am
Just for the curiosity, why does it has to be a solid core wire?
Because multi Filament wires don't go into the holes of a Socket.
And if you put solder on them they might already be too thick to fit into.
And even more critical: These tinned wires tend to break off where the Solder stops making it near to impossible to get the rest out of the socket.
Kind regards
Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

bola_dor
Posts: 138
Joined: Wed Oct 02, 2019 5:32 am

Re: TS1000 with no image :_(

Post by bola_dor »

It's been a while since last post but now with some free time it looks Like I found something.
Just to remember.:
Issue 3 Timex Sinclair boars with no cursor.
RAM, ULA, Z80, CLK inv circuit and TR2 Checked OK.
ULA pin 14 has a low 0.1v so went back to ULA pin 35 in direction to the resonator and found this Yellowish resistor with a black substance to its leads.. I can't measure any current thru it.. (open circuit)
20200504_000615.jpg
I couldn't find an issue 3 board layout but it looks like marked as C6 ( :?: ) in issue 1 that is a 100uF capacitor.. but this doesn't looks like one. I ve seen several boards pictures on the net and It looks like there are many variations in components in this board region..
Anyway.. can any one confirm me the value of this resistor if it is one??
And
How can I check if the resonator is OK?
Thanks

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Erm
Posts: 154
Joined: Thu Jun 20, 2019 7:07 pm

Re: TS1000 with no image :_(

Post by Erm »

It's a capacitor. The black stuff doesn't look encouraging though, but it may still be ok. Does your multimeter have capacitance test mode? Replace it with a modern ceramic one if you have one.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

stroebeljc
Posts: 31
Joined: Thu Apr 23, 2020 6:02 am

Re: TS1000 with no image :_(

Post by stroebeljc »

bola_dor wrote:
Mon May 04, 2020 7:26 am
It's been a while since last post but now with some free time it looks Like I found something.
Just to remember.:
Issue 3 Timex Sinclair boars with no cursor.
RAM, ULA, Z80, CLK inv circuit and TR2 Checked OK.
ULA pin 14 has a low 0.1v so went back to ULA pin 35 in direction to the resonator and found this Yellowish resistor with a black substance to its leads.. I can't measure any current thru it.. (open circuit)20200504_000615.jpg
I couldn't find an issue 3 board layout but it looks like marked as C6 ( :?: ) in issue 1 that is a 100uF capacitor.. but this doesn't looks like one. I ve seen several boards pictures on the net and It looks like there are many variations in components in this board region..
Anyway.. can any one confirm me the value of this resistor if it is one??
And
How can I check if the resonator is OK?
Thanks
It looks to me like a 10.1Ohm resistor in a 100pF capacitor socket. This cap happens to be the connection between the 6.5MHz crystal and the ULA input, so you don't have a clock in the system. This should be replaced by a 100pF cap. Here is the schematic:
ZX81 Schematic portion
ZX81 Schematic portion
John

bola_dor
Posts: 138
Joined: Wed Oct 02, 2019 5:32 am

Re: TS1000 with no image :_(

Post by bola_dor »

It looks to me like a 10.1Ohm resistor in a 100pF capacitor socket. This cap happens to be the connection between the 6.5MHz crystal and the ULA input, so you don't have a clock in the system. This should be replaced by a 100pF cap. Here is the schematic:
schema_ZX81_Fr_zoom.jpg
I've learned now that some caps looks like that.. https://en.m.wikipedia.org/wiki/Electro ... or-coding my other ISSUE 3 TIMEX /Portugal board is exactly like this,
So it's a 100pF capacitor..
Should one of this do the work?
capacitor-ceramico-100pf-101-.jpg
capacitor-ceramico-100pf-101-.jpg (4.12 KiB) Viewed 300 times
Thanks

stroebeljc
Posts: 31
Joined: Thu Apr 23, 2020 6:02 am

Re: TS1000 with no image :_(

Post by stroebeljc »

bola_dor wrote:
Mon May 04, 2020 10:13 pm
I've learned now that some caps looks like that.. https://en.m.wikipedia.org/wiki/Electro ... or-coding my other ISSUE 3 TIMEX /Portugal board is exactly like this,
So it's a 100pF capacitor..
Should one of this do the work?capacitor-ceramico-100pf-101-.jpg
Thanks
Yes (hope the crystal is still okay). If you did find a scope, you can verify an appropriate clock signal by probing pin 6 on the Z80.
John

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Erm
Posts: 154
Joined: Thu Jun 20, 2019 7:07 pm

Re: TS1000 with no image :_(

Post by Erm »

bola_dor wrote:
Mon May 04, 2020 10:13 pm

Should one of this do the work?capacitor-ceramico-100pf-101-.jpg
Thanks
Yes, but whether that sorts your problem is another matter!
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

stroebeljc
Posts: 31
Joined: Thu Apr 23, 2020 6:02 am

Re: TS1000 with no image :_(

Post by stroebeljc »

Erm wrote:
Mon May 04, 2020 11:39 am
It's a capacitor. The black stuff doesn't look encouraging though, but it may still be ok. Does your multimeter have capacitance test mode? Replace it with a modern ceramic one if you have one.
Erm, I stand corrected. I just checked my ZX81 and it has the same component. I've never seen a cap that looked to resistor-y. In any case, if you measure the impedance across this cap it should be off the scale, maybe not right away, but after a few seconds with the probes in place. If it is low, you know the cap is bad. I just measured mine on my working board.
John

bola_dor
Posts: 138
Joined: Wed Oct 02, 2019 5:32 am

Re: TS1000 with no image :_(

Post by bola_dor »

stroebeljc wrote:
Tue May 05, 2020 12:59 am
Erm wrote:
Mon May 04, 2020 11:39 am
It's a capacitor. The black stuff doesn't look encouraging though, but it may still be ok. Does your multimeter have capacitance test mode? Replace it with a modern ceramic one if you have one.
Erm, I stand corrected. I just checked my ZX81 and it has the same component. I've never seen a cap that looked to resistor-y. In any case, if you measure the impedance across this cap it should be off the scale, maybe not right away, but after a few seconds with the probes in place. If it is low, you know the cap is bad. I just measured mine on my working board.
There are several of these Yellowish resistor like capacitors in my board.. and other two of them have black legs.. but I don't have any spares now.. I am going to check is I am just Lucky now with C6 replaced with a new ceramic one..
I don't have an oscilloscope nor a logic probe by now but Z80 pin 6 measured near 5v. So it were not pulsing or pulsing too high... ULA 14 were to low.. so I went Into the resonator.. an found that black legs..
received_694502611361502.jpeg
received_230828371574940.jpeg

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