Trying to fix my ZxSpectrum+

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
Hyuma
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma » Tue Jul 09, 2019 10:06 am

With multimeter in continuity mode i got:

ZTX 651 values:
670, 671, 1, 1

ZTX 751 values:
670, 668, 1497, 1
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Hyuma
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma » Tue Jul 09, 2019 10:27 am

I power on without ram for some seconds and the screen is bit better then before. THERE IS STILL LIFE! :D :lol:

Now with new ZTX 651 and 7651 (without new RAMS)
After some seconds I pressed the reset button and this is result:




this was before:

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Ast A. Moore
Dynamite Dan
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Re: Trying to fix my ZxSpectrum+

Post by Ast A. Moore » Tue Jul 09, 2019 10:38 am

Looks like the CPU can fetch and execute the first few instructions, including a jump, from the ROM, which is great news.
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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.

Hyuma
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Joined: Sat May 18, 2019 6:43 am

Re: Trying to fix my ZxSpectrum+

Post by Hyuma » Tue Jul 09, 2019 10:41 am

Ast A. Moore wrote:
Tue Jul 09, 2019 10:38 am
Looks like the CPU can fetch and execute the first few instructions, including a jump, from the ROM, which is great news.
Wow! I'm really, really, really happy today! Next step will be RAM!
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1024MAK
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Location: Sunny Somerset in the U.K. in Europe

Re: Trying to fix my ZxSpectrum+

Post by 1024MAK » Tue Jul 09, 2019 2:57 pm

Hyuma wrote:
Tue Jul 09, 2019 9:43 am
Can i do some tests now? (I still don't have ram)
Sure! :D

Test the voltages on pins 1,8 and 9 in the position where IC6 was (or any other of the 4116 or equivalent DRAM chip positions). With the negative probe to 0V/GND (e.g. the case of the modulator or the heatsink).

Expected voltages:

PIN 1: between -4V and -5.5V
PIN 8: between 10.8V and 13.2V
PIN 9: between 4.75V and 5.25V

If all these are good, then the next stage is to sort out the ‘lower’ DRAM chips.

Mark
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Hyuma
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Posts: 24
Joined: Sat May 18, 2019 6:43 am

Re: Trying to fix my ZxSpectrum+

Post by Hyuma » Tue Jul 09, 2019 6:28 pm

1024MAK wrote:
Tue Jul 09, 2019 2:57 pm
Hyuma wrote:
Tue Jul 09, 2019 9:43 am
Can i do some tests now? (I still don't have ram)
Sure! :D

Test the voltages on pins 1,8 and 9 in the position where IC6 was (or any other of the 4116 or equivalent DRAM chip positions). With the negative probe to 0V/GND (e.g. the case of the modulator or the heatsink).

Expected voltages:

PIN 1: between -4V and -5.5V
PIN 8: between 10.8V and 13.2V
PIN 9: between 4.75V and 5.25V

If all these are good, then the next stage is to sort out the ‘lower’ DRAM chips.

Mark
pin 1: -5,21v
pni 8: 12,38v
pin 9: 4,98v

yesssssssss! :lol: :lol: :lol:
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Muttley Black
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Re: Trying to fix my ZxSpectrum+

Post by Muttley Black » Wed Jul 10, 2019 6:09 pm

Keep on walking! :)

-If it’s not problem for you, please use Postimage to upload your photos. It is easier as Postimage button is pinned on “reply” mode, but also is way better and safer for you photos to stay online for long time.-
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