Blank screen issue...

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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Ast A. Moore
Rick Dangerous
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Re: Blank screen issue...

Post by Ast A. Moore »

rps wrote: Fri Jun 22, 2018 8:48 am Ok, just checked the chip with the heat sync definately in and it is 40c after 2 min, 45c after another minute and then after 5 min it is settling between 40 and 45c. Does that seem correct?
Perfectly fine. Proceed with the other tests.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
rps
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Re: Blank screen issue...

Post by rps »

awesome. Will run that by my friend as he has the equipment. I’ll get back to you.

Thanks
RPS
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1024MAK
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Re: Blank screen issue...

Post by 1024MAK »

The easiest way to measure the current going to a ZX Spectrum is to buy either an extension lead and cut into it, or buy an cable with an inline switch (remove switch cover, put meter across the connections of the switch).

In both cases you need cables that have a mini barrel plug and line socket, the dimensions of the plug/socket being 5.5mm outside diameter, 2.1mm inside pin diameter.

Search online for "2.1mm power cable switch"
Or "2.1mm power cable"

Mark
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1024MAK
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Re: Blank screen issue...

Post by 1024MAK »

By far the easiest and quickest way to diagnose a RAM fault, is to get the CPU to tell you. There are a number of ways of getting a test program (with runs from ROM, and which does not need any working RAM) to work.

One is to remove the existing ROM chip, maybe modify the PCB ROM configuration jumpers, and fit an EPROM (only practical if you can program/'burn' an EPROM and the existing ROM is in a socket).

Two is to use an expansion device that can take external ROMs (EPROMs, EEPROMs, Flash ROM).

Phil at Retroleum makes a wonderful device that can hold a test ROM image, and has lots of other useful functions. Have a look at his blog entry for his SMART Card device.

It's currently out of stock in his shop (link). He can supply it with a test ROM program ready to use (email him to ask for this).

There are many other devices/interfaces/expansions that can use cartridges (that can hold a test ROM) or which can hold a ROM chip or ROM image directly.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
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