Search found 124 matches

by 1024MAK
Thu Jun 21, 2018 6:37 pm
Forum: Hardware
Topic: ZX Vega+ Discussion
Replies: 59
Views: 1636

Re: ZX Vega+ Discussion

If you are going to judge Clive Sinclair and Alan Sugar, keep in mind that both of them were not exactly known for quality products before they got into the computer business. And keep in mind why the ZX80, ZX81 and the ZX Spectrum were successful, it was being able to come up with a design that was...
by 1024MAK
Wed Jun 20, 2018 6:53 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

First off, ZX Spectrums with a 7805 voltage regulator should only be run with the heatsink fitted. Check that the nut and bolt that hold the heatsink to the 7805 voltage regulator (and to the PCB) are tight. If the 7805 voltage regulator overheats, it will reduce the output voltages. As the DC/DC co...
by 1024MAK
Tue Jun 19, 2018 10:12 am
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

Although not as common as the NEC D780C-1 CPU (a Z80 clone), Sinclair did use Zilog Z80A CPU's in both ZX81's and ZX Spectrum's. And going by the date codes and wave soldered joints, these are the original chips that were fitted.

@rps do you have any expansions? If yes, please list them.

Mark
by 1024MAK
Mon Jun 18, 2018 1:31 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

Ok, so you think lower ram possibly. Does this mean you can rule out upper ram? Or could it still be upper ram? Also, if I was to get parts to make repairs and see where I get with it. Is there ways to test a chip when you remove it from the board? Thanks RPS At this stage, it looks like the ROM, t...
by 1024MAK
Mon Jun 18, 2018 1:23 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

By connecting +5V to pin 5 on IC23, you are overriding the signal from elsewhere in the circuit.This point was deliberately chosen, as the existing signal comes via a resistor (R70) which limits the current flow so that the logic gate that feeds resistor R70 is not damaged. Pin 5 is an input to a lo...
by 1024MAK
Sun Jun 17, 2018 10:40 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

Ast A. Moore wrote:
Sun Jun 17, 2018 7:02 pm
rps wrote:
Sun Jun 17, 2018 6:40 pm
Do you know what number pin the +5v is on the IC23? Can’t find a pin diagram that shows it.
Pin 8 is VDD, pin 16 is ground: http://pdf1.alldatasheet.com/datasheet- ... 4164B.html
Okay, how much beer have you drunk? :lol:

Mark
by 1024MAK
Sun Jun 17, 2018 10:39 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

Hi, Do you know what number pin the +5v is on the IC23? Can’t find a pin diagram that shows it. On IC23 (a 74LS32, quad 2-input OR gates), pin 14 is Vcc (+5V). 0V/GND is on pin 7. I should point out that the method given in the earlier post about how to disable the 'upper' RAM only applies to issue...
by 1024MAK
Sun Jun 17, 2018 2:28 pm
Forum: Hardware
Topic: Blank screen issue...
Replies: 58
Views: 611

Re: Blank screen issue...

The 'lower' RAM are 4116 DRAM (16k bits each) chips which run warm, with some running warmer than others. Sometimes when they fail, they may get hotter. But only if the supply can supply the extra power. Otherwise the switching transistor for the +12V and -5V dies. The 'upper' RAM are 32k bits each ...
by 1024MAK
Fri Jun 15, 2018 11:09 pm
Forum: Hardware
Topic: What floppy disk drive system do you own AND use?
Replies: 9
Views: 170

Re: What floppy disk drive system do you own AND use?

Actually none :) By the way, by Beta 128 you mean Tr-Dos, right? Yes, except that TR-DOS is a, well, DOS —a disk operating system, whereas Beta (128) Disk is the name of the actual interface. Granted, the two were developed by the same company to work in tandem so are essentially synonymous in many...
by 1024MAK
Fri Jun 15, 2018 11:06 pm
Forum: Hardware
Topic: What floppy disk drive system do you own AND use?
Replies: 9
Views: 170

Re: What floppy disk drive system do you own AND use?

Guesser wrote:
Fri Jun 15, 2018 2:52 pm
Hmm, what if you use both 3" and 3.5" drives on a +3, would you vote for both?
"You may select up to 3 options"...
So yes, vote for both if you use both...

Mark