Search found 24 matches

by Erm
Sat Aug 24, 2019 8:08 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

I got my super-duper de-soldering solution and was able to remove the 8 lower RAM chips. Lifted 3 traces but was able to sort those in a neat fashion. Now it all looks good. What sort of screen should I be getting with no lower RAM installed? With empty sockets it's exactly the same as before with t...
by Erm
Sat Aug 24, 2019 1:02 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

I really feel I've learnt something here, about the various voltages on the Spectrum board and where they come from etc.
by Erm
Fri Aug 23, 2019 4:53 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

Well that's even more encouraging then. I may well do the DC-DC mod, but first I'll wait for the new RAM and see how/if it works with that. Thanks for now.
by Erm
Fri Aug 23, 2019 3:07 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

Right, well a little progress, although the screen output is unchanged. I changed C46, R55 is spot on. I changed C74 as a lead fell off. I also changed C61 and D11 (I currently don't have new diodes but stole one from a parts ZX81 - one of the keyboard connector diodes which have the same value writ...
by Erm
Thu Aug 22, 2019 9:26 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

Thanks so much for your time and expertise here, it's not the first time you've helped me with words of wisdom. I think I've done this right: On the input side of the regulator it measures 11.3v. The 12v leg on the RAMs are about 12.3v. Voltage measured on the anode side of D11 is -1.6v. Voltage mea...
by Erm
Wed Aug 21, 2019 7:57 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

Certainly, here it is.
Spectrum48kPCBRight.jpg
by Erm
Wed Aug 21, 2019 2:54 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

On the 4116 chips the +5v and +12v was fine, but the -5v showed a small (0.4+) voltage on all of them.

My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter.
by Erm
Tue Aug 20, 2019 11:01 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

I also ordered the Retroleum SmartCard, perhaps that will help with one or the other.
by Erm
Tue Aug 20, 2019 8:05 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Re: Spectrum 48k Boot pattern

Thanks for the replies. The border isn't white, it seems to be mostly red, but I do remember it being yellow or black too on various re-power-ups, but never white. I de-soldered (I'm ok at desoldering) the Z80, popped a socket on and put a known good Z80 on it - same thing, so put the old one back a...
by Erm
Mon Aug 19, 2019 10:14 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 334

Spectrum 48k Boot pattern

I know this is predominantly ZX81 here, but I'm currently not a member of a Spectrum forum and perhaps someone here can assist. This is what happens to my Spectrum 48k (issue 3b board) when I turn it on (sometimes the border can also be black or yellow, as well as red, shown): https://youtu.be/abHhp...