US Power Supply for ZX Spectrum

[+BoatofCar]

I recently received a ZX Spectrum, and am trying to figure out how to power the thing. The guy that sent it to me cut the leads from the original power supply, and I tried cutting the end off a 9V 800mA wall wart I had lying around and attaching them, positive to positive, negative to negative. When I powered it on, the picture on the monitor flashed a few times and then went black. Then I tried a normal 9V 500mA Radio Shack power supply I had, and it caused the Speccy to hum, but no picture at all appeared.

 

For the picture, I believe from looking inside the machine that the composite mod has already been performed, and I'm running that through a GBS8200 board into a VGA monitor. So it's not as if there aren't enough variables going on

 

Any help is much appreciated!

[carlsson]

It should be 9V DC, centre polarity negative (same as Genesis, Famicom, Jaguar etc). The humming sounds like you swapped the polarity the wrong way. I did this once, and it lead to the Spectrum not working anymore. With a bit of luck, you just zapped the 7805 voltage resistor, but you may have suffered more damage than so.

 

By the way, does the GBS-8200 accept a composite signal? Well, I suppose you could feed it either as red, green or blue but then you would want to split it so you can feed it as sync at the same time.

Edited September 5, 2016 by carlsson

[+BoatofCar]

Well, I hope I didn't do too much damage. Why did they not add an LED on the Spectrum or something to be able to test it without a monitor? The GBS-8200 might be the culprit too, I use it for connecting an A500 to an LCD, but not through the composite input.

[carlsson]

I read that you might be able to use the Y input on the YPbPr to get an image on the GBS:

https://ianstedman.wordpress.com/gbs-82xx-experiments/

 

Unfortunately a LED won't tell the entire truth. Many C64 owners have found it lits, but won't boot so the LED would need to be connected in such way it turns on after the ROM boot-up sequence has passed.

 

A few links on wrong polarity and what you might need to do to fix it.

http://comp.sys.sinclair.narkive.com/GqImfscQ/zx-spectrum-and-wrong-power-supply-polarity

https://www.tablix.org/~avian/blog/archives/2007/06/another_zx_spectrum_s_near_death_experience/

http://users.tpg.com.au/users/romsey/

[+BoatofCar]

Situation is resolved. Even though the Y input on the YPbPr part of the GBS gave me an image on my Apple II, it was no dice on the Speccy. I ran it through a 1702 and it worked like a charm, albeit in PAL black and white mode. I used the original adapter configuration I mentioned in the OP and it fired right up. Thanks for your help in causing me to investigate the GBS, it turned out to be the culprit.

[carlsson]

Phew! That saved you from hours of "fun".