Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Cenoura54
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Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Mon Apr 16, 2018 1:32 am

My ZX Spectrum +2 (Grey UK) was working but the connector of the PSU wasn't the correct size for the power jack.
After picking um 2 PSU's I tried one and notice no power led or video. After that I cheked the PSU's and was one with the wrong poles for the Spectrum.
I changed the voltage regulator and the Spectrum started working I can load games, I ear the sound of the loading the sound of the keyboard but I have no image unfortunetly. I tested the reset on the CPU and I can see in the multimeter when I press the reset and when It goes down and start loading again.
Long story short work everything but composite video.

PS: I dont tried RGB I'm just trying to make composite work first.

McKlaud
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by McKlaud » Mon Apr 16, 2018 7:30 am

Have a look and measure a supplying voltage to TEA200 chip. The PAL encoder requires 12V supply (pin 11 on it).
Claudius
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Cenoura54
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Mon Apr 16, 2018 2:25 pm

I'm just getting 6.5v on pin 11 mesuring from the power jack to the encoder.
I'm using a 9V power brick should I use a 12v one? If yes what is the far I can go with Amp's?

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1024MAK
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by 1024MAK » Mon Apr 16, 2018 7:49 pm

It's likely that TR8 (ZTX213) and TR9 (ZTX650, or ZTX651 or ZTX653) have been damaged.

I suggest replacing TR9 first.

If you test across C41 connections (or between D20 cathode (K) and 0V/GND) when the internal DC/DC circuit is working correctly, your meter should show about +12V even if the input supply to the machine is only +9V.

The schematic is here

Mark

Cenoura54
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Mon Apr 16, 2018 8:35 pm

1024MAK wrote:
Mon Apr 16, 2018 7:49 pm
It's likely that TR8 (ZTX213) and TR9 (ZTX650, or ZTX651 or ZTX653) have been damaged.

I suggest replacing TR9 first.

If you test across C41 connections (or between D20 cathode (K) and 0V/GND) when the internal DC/DC circuit is working correctly, your meter should show about +12V even if the input supply to the machine is only +9V.

The schematic is here

Mark
My suply is showing 10.8V max on the power conector and 8V max on the video chip pin 11. I already changed the ZTX650 with a BC548 I think It should work It's a all porpuse NPN. I use this one because I doesnt have any close NPN around or I can't find one in the maybe 20 types I have. TR8 don't try it yet.

PS: The TR3 is making short in one leg. Maybe is this one.

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1024MAK
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by 1024MAK » Tue Apr 17, 2018 12:26 am

TR9 has to be a fast switching power transistor. I'm not sure a BC548 will work (the BC548 and similar transistors are for audio frequency low power amplifier applications). Certainly a BC548 will not last long in the 16k and 48k models (although in these there is a higher load on the +12V supply).

I'll try to find the list of equivalents for the ZTX650, ZTX651, ZTX 653. I'll post the link once I have found it.

The DC/DC converter formed by TR8, TR9 and associated components takes the unregulated and nominal '+9V' input (which can be anywhere between +7.5V and +12V) and converts it to a regulated +12V, -12V and a -5V supply. It is also worthwhile renewing any electrolytic capacitors in this circuit as well.

TR3 is supposed to have it's base and collector connected according to the schematic (link). I've not checked this on an actual board, as I'm not had a problem with TR3 before.

Mark

Cenoura54
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Tue Apr 17, 2018 12:55 am

1024MAK wrote:
Tue Apr 17, 2018 12:26 am
TR9 has to be a fast switching power transistor. I'm not sure a BC548 will work (the BC548 and similar transistors are for audio frequency low power amplifier applications). Certainly a BC548 will not last long in the 16k and 48k models (although in these there is a higher load on the +12V supply).

I'll try to find the list of equivalents for the ZTX650, ZTX651, ZTX 653. I'll post the link once I have found it.

The DC/DC converter formed by TR8, TR9 and associated components takes the unregulated and nominal '+9V' input (which can be anywhere between +7.5V and +12V) and converts it to a regulated +12V and a -5V supply. It is also worthwhile renewing any electrolytic capacitors in this circuit as well.

TR3 is supposed to have it's base and collector connected according to the schematic (link). I've not checked this on an actual board, as I'm not had a problem with TR3 before.

Mark
TR3 was good I tested it out of the board and give the 700's in both outer legs. But the ZTX650 was 1 outer leg shorted. If I can do it wit diodes I dont mind do it. because its all working but no video unfortunetly.
Thanks a lot if you can find it. I found some equivalent for ztx650 but I have none of them.

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1024MAK
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by 1024MAK » Tue Apr 17, 2018 2:35 am

Note, the +12V and -5V are also on the edge-connector.

If you have a regulated 12V supply, you could always feed it in via either the edge-connector, or via D20 cathode connection. Of course, check, test and double check the polarity ;) You still need a nominal +9V on the power jack input for the 7805 voltage regulator etc.

Mark

Cenoura54
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Tue Apr 17, 2018 4:50 am

1024MAK wrote:
Tue Apr 17, 2018 2:35 am
Note, the +12V and -5V are also on the edge-connector.

If you have a regulated 12V supply, you could always feed it in via either the edge-connector, or via D20 cathode connection. Of course, check, test and double check the polarity ;) You still need a nominal +9V on the power jack input for the 7805 voltage regulator etc.

Mark
Thanks I will give it a try tomorrow. I will try a 9v 2.5A to see If Iget any diference in voltage. I'm using a 9V 1200mA and unpluged give me 14.5v but pluged I just get 10.8v at the ZX connector. Could be lack of amperage maybe. The amperage increase and the voltage draw. Maybe thats why I'm not even getting 12v at pin 11.

Cenoura54
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Re: Sinclair 128k ZX Spectrum +2 Grey UK no video after inverted polarity

Post by Cenoura54 » Tue Apr 17, 2018 1:55 pm

I manage to get the 12v to pin 11 but still no signal. I think the spectrum it's oficially dead. :(

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