ZX Spectrum display fault - UK Vintage Radio Repair and Restoration Discussion Forum

kickfest · 4th Apr 2015, 4:57 pm

Hi all

Wondering if anyone here has any experience with ZX Spectrum repair, as I've recently picked up a 48k which wouldn't power on. After replacing the voltage regulator it now powers on successfully but it's still quite poorly.

When it powers on, black pixels being to appear randomly at the top of the screen
Video: https://youtu.be/_EsnNRVrpQY

Attempting LOAD "" turns the screen into a random mess of characters (picture attached).

I know which end of a soldering iron to hold, but I'm really quite novice when it comes to these things so if anyone has any suggestions then I'd be really grateful! I have a working Spectrum+ as well if that's any help.

jay_oldstuff · 4th Apr 2015, 7:08 pm

Personally the first thing I would do is try a replacement ULA purely because I've seen smiler symptoms linked to a faulty ULA it could also be a ram fault or a fault in some of the associated glue logic. I can highly recommend watching the videos on YouTube by JoulesperCoulomb he goes through the basic fault finding and repair of the 48k spectrum and his videos are a very good starting point.

Jay

Mad Mal · 24th Jul 2016, 5:21 pm

That's what I suspect. also the transistor and electrolytics associated with voltage on the board. There's not that much room in the Spectrum case. I put mine in a D'kTronics keyboard and when, after a year's worth of faithful service, that transistor failed. I replaced it with a TIP 31... no more power problems. The ULA went through a couple of revisions during production, but all versions were pin for pin compatible. It was changes to the internal mask that helped with heat dissipation in think.

4th Apr 2015, 4:57 pm	#1
kickfest Retired Dormant Member Join Date: Apr 2015 Location: London, UK. Posts: 1	ZX Spectrum display fault Hi all Wondering if anyone here has any experience with ZX Spectrum repair, as I've recently picked up a 48k which wouldn't power on. After replacing the voltage regulator it now powers on successfully but it's still quite poorly. When it powers on, black pixels being to appear randomly at the top of the screen Video: https://youtu.be/_EsnNRVrpQY Attempting LOAD "" turns the screen into a random mess of characters (picture attached). I know which end of a soldering iron to hold, but I'm really quite novice when it comes to these things so if anyone has any suggestions then I'd be really grateful! I have a working Spectrum+ as well if that's any help. Attached Thumbnails

4th Apr 2015, 7:08 pm	#2
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Personally the first thing I would do is try a replacement ULA purely because I've seen smiler symptoms linked to a faulty ULA it could also be a ram fault or a fault in some of the associated glue logic. I can highly recommend watching the videos on YouTube by JoulesperCoulomb he goes through the basic fault finding and repair of the 48k spectrum and his videos are a very good starting point. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

24th Jul 2016, 5:21 pm	#3
Mad Mal Tetrode Join Date: Jul 2016 Location: Spennymoor, County Durham, UK. Posts: 69	Re: ZX Spectrum display fault That's what I suspect. also the transistor and electrolytics associated with voltage on the board. There's not that much room in the Spectrum case. I put mine in a D'kTronics keyboard and when, after a year's worth of faithful service, that transistor failed. I replaced it with a TIP 31... no more power problems. The ULA went through a couple of revisions during production, but all versions were pin for pin compatible. It was changes to the internal mask that helped with heat dissipation in think.