Search found 5103 matches

by 1024MAK
Wed Jun 10, 2020 11:17 am
Forum: Hardware
Topic: My first ZX80.
Replies: 78
Views: 20757

Re: My first ZX80.

The ZX81 has additional hardware so that it can compute and display (known as SLOW mode on the ZX81). On a ZX81, FAST mode is equivalent to the display system on a ZX80. That is when processing a program, video output is no longer generated (so the screen blanks) until either the program waits for u...
by 1024MAK
Wed Jun 10, 2020 10:55 am
Forum: Hardware
Topic: Help needed with a unstable +2 grey
Replies: 16
Views: 14667

Re: Help needed with a unstable +2 grey

The PAL pin 9 goes to a (19B)... I can't locate (19B) IC7 (PAL) pin 9 is an input, it’s the /WR (also written ‘WRL’) line from the Z80 CPU (IC9) pin 22. This line goes to various other places including the edge connector contact 19 on the component side (which is what 19B could be referring to). Al...
by 1024MAK
Tue Jun 09, 2020 2:22 pm
Forum: Hardware
Topic: lost in modifications 4A
Replies: 11
Views: 12646

Re: lost in modifications 4A

i will recap the whole speccy , and then verify the voltages , as all 22 mfd became +40mfd ............... :?: :?: :?: Unless shown otherwise, a 22uF electrolytic capacitor should be replaced with a 22uF electrolytic capacitor. On a ZX Spectrum board, there is no advantage in fitting larger electro...
by 1024MAK
Tue Jun 09, 2020 10:22 am
Forum: Hardware
Topic: Help needed with a unstable +2 grey
Replies: 16
Views: 14667

Re: Help needed with a unstable +2 grey

Will the machine run BASIC programs? If yes, can you please try this: 10 CLS : BORDER 2 : INPUT “speed”,s 20 FOR y=0 TO 21 30 FOR x=0 TO 31 40 PRINT AT y,x;CHR$ 134 50 PAUSE s 60 PRINT AT y,x;CHR$ 137 70 PAUSE s 80 PRINT AT y,x;CHR$ 32 90 NEXT x 100 NEXT y 110 GO TO 20 When you RUN it, enter a speed...
by 1024MAK
Tue Jun 09, 2020 9:05 am
Forum: Hardware
Topic: Help needed with a unstable +2 grey
Replies: 16
Views: 14667

Re: Help needed with a unstable +2 grey

Please ignore the /M1 report. The diagnostic test was originally designed to run on an external diagnostic board which includes some hardware so that the Z80 /M1 line can be tested. If the diagnostic board is not present, it prints the report you see, telling you that it can’t detect this board. The...
by 1024MAK
Mon Jun 08, 2020 7:08 pm
Forum: Hardware
Topic: Maximal restoration of ZX81
Replies: 22
Views: 6506

Re: Maximal restoration of ZX81

In my experience, the greatest causes of failures of electronic systems in general is the shock of powering on (or due to a rapid power off/on due to a power blip) or due to thermal cycling. And not due to the average temperature reached in a system when operating well within its normal operating sp...
by 1024MAK
Mon Jun 08, 2020 6:16 pm
Forum: Hardware
Topic: Maximal restoration of ZX81
Replies: 22
Views: 6506

Re: Maximal restoration of ZX81

There is lots of useful information on semiconductors and heatsinking here , including the calculations needed to work out the temperatures or heat flow values. However the important points are these: The ULA runs warm because that is due to the way it was designed, so it’s normal. The only ULA chip...
by 1024MAK
Mon Jun 08, 2020 2:39 pm
Forum: Hardware
Topic: Maximal restoration of ZX81
Replies: 22
Views: 6506

Re: Maximal restoration of ZX81

The Byte Attic wrote: Mon Jun 08, 2020 1:54 pm Lots of quotes...
Moggy wrote: Mon Jun 08, 2020 2:06 pm Lots of quotes...
There is no need to keep quoting large amounts of text. Use the “Post Reply” button instead or at least edit the quoted text to a reasonable amount that is relevant.

Otherwise I will have to step in and aggressively edit posts.

Mark
by 1024MAK
Mon Jun 08, 2020 1:49 pm
Forum: Hardware
Topic: Maximal restoration of ZX81
Replies: 22
Views: 6506

Re: Maximal restoration of ZX81

The AT49F001AN datasheet does not specify a data retention figure, but modern EEPROM/flash ROM devices typically have data retention times of 25 years plus if used as a ROM. 1980s EPROMs often were said to have data retention times of 10 years, but some are now still working at 30 to 40 years... Mas...
by 1024MAK
Mon Jun 08, 2020 1:35 pm
Forum: SALES
Topic: Lardo buys another zeddy
Replies: 317
Views: 272522

Re: Lardo buys another zeddy

Ahh, one with a stick on hard key keyboard.

I had a Zeddy with one of those, but the stick on hard key keyboard fell off! :lol:

Mark