Every now and again I like to have a move around in my retro room and possibly swap out some systems. Well I decided that to represent the Spectrum, I would get one of my 128K Spectrums connected up. I grabbed one off the shelf and plugged it all in ready to sit down and have a play. Only to find out, this one had become faulty!
When turning it on using the RGB scart cable, the picture was pretty much black. But this wasn’t a dead Spectrum, as if you looked closely you could see that the computer itself was running fine.
It’s not very clear in the picture but in the center of the screen you can just make out the 128k menu.
This then was more of an issue with the video signal, specifically the blanking signal on the scart cable. Just to rule out a bad cable I tested my other toastrack and that displayed fine.
There is sometimes an issue with Spectrums and certain TVs when using the RGB scart cable, and there is a quick mod you can do to increase the blanking voltage which helps in this situation. But I didn’t think that was what was going on here, and I was pretty sure I had already done that mod on this system at some point.
I opened it up and checked the blanking voltage which was at 1.45v. Yeah, there is something not happy here. Another common fault with these machines which would match the issue I was seeing, is the two transistors, TR4 and TR5.
Taking TR4 off the board and giving it a test, confirmed my suspicions.
That doesn’t look much like a transistor to me! So, a quick trip to eBay and a few days waiting for some replacements to arrive.
I did test TR5, and it actually tested OK. But I replaced it anyway to be safe. Sometimes, if you only replace TR4, TR5 can end up damaging the new replacement.
Anyway, we are now back to having a decent voltage on the blanking circuit, and yes, I had already done the blanking mod on this one.
Time to put it back together and give it a test!
All working 😀
Unfortunately, that used up my spare time this evening, so i don’t actually get to sit down and play a game. Slightly, will have to put his adventure on hold until next time.