TS1000 with no image :_(

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Erm
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Re: TS1000 with no image :_(

Post by Erm »

I thought they were odd resistors when I first saw them too!

Is there continuity between the solder side and the corroded leg? It can't hurt changing them but I don't think they tend to fail that often.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
stroebeljc
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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)
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
With the ULA taken out, have you verified that the impedance at pin 35 of the ULA is 18kOhm?
John
bola_dor
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Re: TS1000 with no image :_(

Post by bola_dor »

stroebeljc wrote: Wed May 06, 2020 12:21 am With the ULA taken out, have you verified that the impedance at pin 35 of the ULA is 18kOhm?
Well .. not.. I know ULA is OK as I checked it with other known ULA and this ULA in the other board works fine..
I changed those capacitors but remains the same..
What would indicate ULA's pin 35 impedance?
Thanks
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
bola_dor
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Re: TS1000 with no image :_(

Post by bola_dor »

Erm wrote: Tue May 05, 2020 12:28 pm I thought they were odd resistors when I first saw them too!

Is there continuity between the solder side and the corroded leg? It can't hurt changing them but I don't think they tend to fail that often.
I've already desoldered an changed them.. so I don't know :roll:
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
stroebeljc
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Re: TS1000 with no image :_(

Post by stroebeljc »

bola_dor wrote: Wed May 06, 2020 6:51 am
stroebeljc wrote: Wed May 06, 2020 12:21 am With the ULA taken out, have you verified that the impedance at pin 35 of the ULA is 18kOhm?
Well .. not.. I know ULA is OK as I checked it with other known ULA and this ULA in the other board works fine..
I changed those capacitors but remains the same..
What would indicate ULA's pin 35 impedance?
Thanks
I mean the impedance between board ground and the ULA socket pin 35 with the ULA removed, not the impedance of the ULA itself.
John
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1024MAK
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Re: TS1000 with no image :_(

Post by 1024MAK »

Maybe this helps... capacitor code code chart showing axial capacitor coding.

You can still get axial ceramic capacitors, but most don’t use a colour code.

The black stuff on the leads may be tarnish, as back then some components had some silver in the plating on the leads. Underneath, the copper conductor may be okay.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
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bola_dor
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Re: TS1000 with no image :_(

Post by bola_dor »

1024MAK wrote: Wed May 06, 2020 5:22 pm Maybe this helps... capacitor code code chart showing axial capacitor coding.

You can still get axial ceramic capacitors, but most don’t use a colour code.

The black stuff on the leads may be tarnish, as back then some components had some silver in the plating on the leads. Underneath, the copper conductor may be okay.

Mark
Thanks.. I've already replaced both with corresponding 100pF and 47pF ceramic disk ones. I preserved the originals in case they are good and want to keep the original look.. I have an identical other board and none of these axial caps have black leads..
Anyway machine is still not working. ULA pin 14 is to low .. and no video. I think the resonator may not be good. Unfortunately I don have, while the quarantine persists, access to an oscilloscope..
Do you think that to desolder the one in the working board and resolder it here just to make diagnosis is to risky? I am talking about the resonator..
to get a new one at my country is not easy and buying it is really difficult as our @#$%% government has blocked PayPal payments.. (yes in XXI century)...
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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1024MAK
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Re: TS1000 with no image :_(

Post by 1024MAK »

So, let me recap... (point out if I get anything wrong)
  • The ULA works in another board,
  • A static voltage test shows that TR2 and associated components appear to be okay,
  • C6 has been replaced with a new capacitor.
Now, the ULA should produce the CPU clock signal regardless of anything else, as long as it has power and it’s own 6.5MHz oscillator (based on the resonator) works.

Before getting to swapping the resonator, I think it’s wise to check / test these items (if you have already done any of this, just say):
  • Is there power to the ULA? Test across pin 40 (+5V) and pin 34 (0V/GND)? Please test on the pins of the chip.
  • Is the ULA socket good? No damaged, bent or distorted contacts, and none which have lost their springiness?
  • Have you checked and tested for dry joints and broken/cracked PCB tracks?
  • Does R4 test okay?
  • Only two out of the three pins are used on the resonator, are the PCB tracks okay for the two in use pins, and is the third pin free of any short circuits?
I’ve never tried, but a 6.5MHz crystal may work in place of a 6.5MHz resonator.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: TS1000 with no image :_(

Post by 1024MAK »

Another thing to try, is to add an extra 1kΩ resistor.

Here are two photos showing where the factory has added the extra resistor:
63C4024A-EA0B-4748-8337-E2D951B9319B.jpeg
82CAEB0E-2B14-493E-A003-1A4479662BAB.jpeg
This extra 1kΩ resistor is wired from the junction of C6 / X1 (the resonator) and 0V/GND. I don’t know why it is fitted to some boards and not others.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
bola_dor
Posts: 398
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Re: TS1000 with no image :_(

Post by bola_dor »

1024MAK wrote: Thu May 07, 2020 1:07 am So, let me recap... (point out if I get anything wrong)
  • The ULA works in another board.
Checked
[*]A static voltage test shows that TR2 and associated components appear to be okay,
Checked
[*]C6 has been replaced with a new capacitor.
[/list]
Checked, also C7
Now, the ULA should produce the CPU clock signal regardless of anything else, as long as it has power and it’s own 6.5MHz oscillator (based on the resonator) works.

Before getting to swapping the resonator, I think it’s wise to check / test these items (if you have already done any of this, just say):
  • Is there power to the ULA? Test across pin 40 (+5V) and pin 34 (0V/GND)? Please test on the pins of the chip.
Checked
[*]Is the ULA socket good? No damaged, bent or distorted contacts, and none which have lost their springiness?
Checked
[*]Have you checked and tested for dry joints and broken/cracked PCB tracks?
Checked as far as I can see
[*]Does R4 test okay?
Checked 19.4 Kohm but I think is OK
[*]Only two out of the three pins are used on the resonator, are the PCB tracks okay for the two in use pins, and is the third pin free of any short circuits?
[/list]
Checked,
20200506_213427.jpg
20200506_215932.jpg
mine has the three leads soldered

I’ve never tried, but a 6.5MHz crystal may work in place of a 6.5MHz resonator.

Mark
Thanks a lot!
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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