ZX +128 12v rail issues

bola_dor
Posts: 399
Joined: Wed Oct 02, 2019 5:32 am

Re: ZX +128 12v rail issues

Post by bola_dor »

1024MAK wrote: Fri Mar 10, 2023 1:32 pm I can’t remember how power hungry the TEA2000 is. But it’s not going to be too much for a boost converter run off the +5V rail.

The alternative arrangement would be to link the +9V and +12V rails again (and remove any of the existing components that would not like this) and use a 12V regulated PSU. The downside being (1) the 7805 and heatsink would get hotter and (2) it will only work correctly with a 12V regulated PSU.

Mark
I guess that's how it was working, luckily it never got a too high voltage from a non regulated PSU.
I case I decided to keep struggling for the original design what would be thebnext step? I,ve changed all electrolytics involved but the 4.7uF one (5v are really smooth at tr5 emiter) both transistor changed with the replacements I can get here..
Change diodes? Can I use common rectifier ones like 4007? or should I use signal ones like 1n4148?
What can I check at tr4 and Tr5?
And how do I check the coil? I can't replace it easily unless for a (really) dead 48k board I can use as a Donor...
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: ZX +128 12v rail issues

Post by 1024MAK »

Bit busy at the moment. If I don’t reply within three hours, quote my post to remind me.

Oh, the diodes need to be fast types, 1N400X are far too slow.

Mark
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1024MAK
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Re: ZX +128 12v rail issues

Post by 1024MAK »

Right, not going to get back to this tonight, sorry.
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
bola_dor
Posts: 399
Joined: Wed Oct 02, 2019 5:32 am

Re: ZX +128 12v rail issues

Post by bola_dor »

1024MAK wrote: Fri Mar 10, 2023 10:23 pm Right, not going to get back to this tonight, sorry.
Don't worry I had a busy weekend too..
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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