ZX+ lower ram diagnostic help

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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Muttley Black
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Re: ZX+ lower ram diagnostic help

Post by Muttley Black »

I have about the same problem with [mention]Jayhay[/mention], in issue 3B *modified* board.

I have replaced all capacitors, the transistors TR4 /TR5, the D12 *(r79)* 2k2 was burned so i put new one, i swap ULA / CPU /ROM from a working board, but not any change on the screen. Both lower and upper ram was tested on andruino tester. Voltages (-5,+12,+5,gnd) are ok. All six 74LSxxx are tested on IC tester and they are in working order. The only thing that i am afraid and i going to try it, is to replace the sockets with turned pin ones, cause i am sensing loose connectivity in some upper ram ICs.

Tip that [mention]1024MAK[/mention] post with +5 volts on pin5 of 74ls32n do be able to start the zx in 16k mod also didn't post something new on the screen.


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I am keeping my fingers crossed for succeed repair! :lol:
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Ast A. Moore
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Re: ZX+ lower ram diagnostic help

Post by Ast A. Moore »

Remove all upper RAM ICs and retest. Then, with the upper RAM ICs still removed, try swapping the lower RAM ICs around and test again. See if that makes any difference.
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1024MAK
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Re: ZX+ lower ram diagnostic help

Post by 1024MAK »

I generally recommend that with threads where we are discussing repairs, that members start a new thread rather than add to an existing thread. Having a separate threat saves any confusion as people try to help, but get confused over who is reporting what with which board / machine.

If a common issue is later found, then a link or links can always be added to point to other relevant threads or posts.

With all these tricky faults, it is also helpful if the member also states what test gear they have, or have access to.
Useful test gear includes (but is not limited to), decent digital multimeter, logic probe, logic analyser, oscilloscope.

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Muttley Black
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Re: ZX+ lower ram diagnostic help

Post by Muttley Black »

i do that.
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Ast A. Moore
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Re: ZX+ lower ram diagnostic help

Post by Ast A. Moore »

1024MAK wrote: Fri May 03, 2019 8:42 am I generally recommend that with threads where we are discussing repairs, that members start a new thread rather than add to an existing thread.
Seconded.
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.
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Muttley Black
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Re: ZX+ lower ram diagnostic help

Post by Muttley Black »

I just started a new thread.
Sorry for the mess.
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