Since the last couple of reviews I haven’t really done much updating here, although there has been plenty going on. I’ll start with the venerable ZX Spectrum stuff I have to report. In a box of Spectrum stuff I received last year were two Spectrum 48k + which are now both working but weren’t before, additionally there were two very sorry looking boards, one an issue 2 and one an issue 4S. Visiting the Spectrum4Ever Facebook page regularly and seeing people repairing Speccys gave me a taste for giving it a bit more of a go so I dived in. Here are the two boards, Issue 2 on the right was the one we decided to repair..
So first things first I used the Initial Tests video by JoulesPerColoumbe
on YouTube to determine the first steps to repair. One of the first things on old computers and equipment is always to replace the capacitors so I ordered some from Ebay, you can find complete kits of caps to save time hunting for the individual ones so I did that. Once the capacitors were all new, I did the tests and found that mostly all of the power circuit was screwed, probably due to the damaged coil you can see in the picture. So that was TR4, TR5, (ZTX transistors) and the 5v (7805) regulator and that coil to be replaced before any power was applied. While the soldering iron was hot I also added a cable to carry the video signal, as the RF modulator was missing, linking it to the points on the board where composite mods are usually taken from. Now the board looks like this
Going back to the initial tests, they were much more like the readings in the Youtube video. The board was now ready for power to be applied, on plugging in there was a loud buzzing but that is normal, voltages were close to the expected ranges (+5v, -5v, and +12v) so on with the next step which is to plug it into a composite TV input. There was a picture (good sign) but it was only a green border and black inside with red flecks (not so good). This brings me to one of my recent purchases, a Retroleum supplied SD Card adapter
and also diagnostics board which was perfect for this project. I tested it on one of my other working Speccys first, and it reported that it had an upper memory fault, and even tells me which IC would need replacing, excellent more repairs to do. On plugging it into my newly repaired board I managed to get a picture while it did its testing and told me lower ram chip IC10 was faulty (that would explain the display because apparently lower ram is where the display is stored) and also an upper ram chip IC17 is duff.
Having tried unsuccessfully to remove some ram ICs from the other board, I bit the bullet and ordered some from http://www.bytedelight.com/
so the wait is on.