[solved] 16/48 OK Composite, but ZX-HD cannot show

User avatar
BarryN
Posts: 151
Joined: Thu Nov 09, 2017 11:34 pm

Re: [solved] 16/48 OK Composite, but ZX-HD cannot show

Post by BarryN »

Tiger wrote: Fri Oct 08, 2021 11:46 pm The + outside is as driving on the left - typical British ;) As 1024MAK told the ZX power is unstable and reduces under load. A modern 9V regulator is not necessary.
I use a modern 9VDC regulated supply and it causes my Timex Sinclair 1000 to run MUCH cooler as the input voltage to the internal 5V regulator is reduced. The original supply (which stopped working a long time ago) output about 10 1/2 to 11 volts under load. The new supply outputs a constant 9VDC, which is a couple volts lower but still plenty to allow the internal 5V regulator to do it's job but run much cooler.
User avatar
BarryN
Posts: 151
Joined: Thu Nov 09, 2017 11:34 pm

Re: [solved] 16/48 OK Composite, but ZX-HD cannot show

Post by BarryN »

BarryN wrote: Sat Oct 09, 2021 12:04 am
Tiger wrote: Fri Oct 08, 2021 11:46 pm The + outside is as driving on the left - typical British ;) As 1024MAK told the ZX power is unstable and reduces under load. A modern 9V regulator is not necessary.
I use a modern 9VDC regulated supply and it causes my Timex Sinclair 1000 to run MUCH cooler as the input voltage to the internal 5V regulator is reduced. The original supply (which stopped working a long time ago) output about 10 1/2 to 11 volts under load. The new supply outputs a constant 9VDC, which is a couple volts lower but still plenty to allow the internal 5V regulator to do it's job but run much cooler.
Some people replace the 7805 internally with a modern switching regulator module. That will REALLY reduce the heat inside the case if you do that.
User avatar
1024MAK
Posts: 5102
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: [solved] 16/48 OK Composite, but ZX-HD cannot show

Post by 1024MAK »

So…

If the original power supply is working, then it’s fine. It uses a isolated transformer and has a over temperature fuse, so it’s safe. There is no need to replace it unless you want to.

A modern 9V power supply (which will be regulated) will allow the computer to run slightly cooler. But please buy a good brand or buy from a shop or store that you trust. Buying on a well known auction site, or a certain site named like an area of forest in South America does not mean that it’s unsafe, but it is harder to tell the quality of what you are getting. The reason I point this out, is because very cheap units made in China don’t comply with reasonable safety standards.

An alternative to getting a new power supply, if you want the computer to run slightly cooler, is to get some suitable silicon rectifier diodes (well two or three) and wire in series in the power lead to the computer. This will drop the voltage slightly.

Or as said above, you can replace the 7805 voltage regulator with a DC/DC converter / switching regulator like a Recom or Traco Power or similar. These don’t need the heatsink.

There is and never was any kind of standard for the polarity of the barrel type mini DC power jacks. There are still devices and gadgets made today where the outside is + positive.

And occasionally you will find these being used for a low voltage AC transformer output…

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.
User avatar
tridy
Posts: 24
Joined: Wed Oct 06, 2021 6:51 pm
Location: Stockholm, Sweden

Re: [solved] 16/48 OK Composite, but ZX-HD cannot show

Post by tridy »

Thanks! I will continue using the original 12(?)V power supply. It was originally bought/sold in Sweden, and even though it looks like an original but it does not have any Sinclair markings on it. I also ordered a new power supply from byte delight for the toaster that did not have a power supply, so I will have a backup plan just in case.
Post Reply