ZX spectrum spider mod
ZX spectrum spider mod
Hi, starting to repair a ZX Specturm Issue 2 board. Power is ok and clock is ok but no activity on Z80 M1 pin so removed and tested the Z80 and sure enough it is dead.
So planning next steps but this issue 2 board has the spider mod. Am I OK to continue testing for now without this mod and is there a better place to install the mod rather than over the Z80?
Thanks, any help much appreciated.
So planning next steps but this issue 2 board has the spider mod. Am I OK to continue testing for now without this mod and is there a better place to install the mod rather than over the Z80?
Thanks, any help much appreciated.
- 1024MAK
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Re: ZX spectrum spider mod
Yes, it will work in BASIC without the spider transistor. It's machine code programs (games) that access I/O ports (the ULA or joystick interface) that would experience problems.
And yes, there are alternative positions for this transistor. I'll try to find a photo showing a better position.
Mark
And yes, there are alternative positions for this transistor. I'll try to find a photo showing a better position.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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ZX81 Chip Pin-outs
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There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb

Spring approaching...
- 1024MAK
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Re: ZX spectrum spider mod
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert 
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Spring approaching...
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp


There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb

Spring approaching...
Re: ZX spectrum spider mod
Thanks for that, replaced Z80 and now getting bus activity and M1. But screen as follows.
I can see activity on all lower RAM Dout pins, so think my next step will be to socket the ROM and replace with a Diagnostics ROM. I do have a working ULA, so as this is socketed may swap anyway just in case.
Any hints or tips much appreciated.
Thanks
Rob
I can see activity on all lower RAM Dout pins, so think my next step will be to socket the ROM and replace with a Diagnostics ROM. I do have a working ULA, so as this is socketed may swap anyway just in case.
Any hints or tips much appreciated.
Thanks
Rob
- 1024MAK
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Re: ZX spectrum spider mod
That looks like a problem with the 'lower' DRAM, or a problem with the busses that means the ULA is having trouble getting screen data.
In your photo, the border is white. Does it go white at every power up (NOT reset)? Try six to ten times. If it always goes white, this indicates that the Z80 is able to read the very first part of the ROM.
Mark
In your photo, the border is white. Does it go white at every power up (NOT reset)? Try six to ten times. If it always goes white, this indicates that the Z80 is able to read the very first part of the ROM.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert 
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Spring approaching...
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp


There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb

Spring approaching...
Re: ZX spectrum spider mod
Thanks, border is always white? Guess I need to eliminate the lower RAM as a first bet?
Thanks
Rob
Thanks
Rob
Re: ZX spectrum spider mod
Well that's a turn up for the books.
I took the ULA out and placed in my other working Spectrum, and worked as expected.
Could not be bothered to swap back, so inserted the ULA from my other working Spectrum and Bob's your uncle.
Still can't quite believe it, so may swap back the ULAs. What's the betting.
I took the ULA out and placed in my other working Spectrum, and worked as expected.
Could not be bothered to swap back, so inserted the ULA from my other working Spectrum and Bob's your uncle.
Still can't quite believe it, so may swap back the ULAs. What's the betting.
- 1024MAK
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Re: ZX spectrum spider mod
Possible poor pin/socket connection.
Are both boards issue two, or is the other board a different issue board?
Are both ULA chips the same, or are they different versions?
Mark
Are both boards issue two, or is the other board a different issue board?
Are both ULA chips the same, or are they different versions?
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert 
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Spring approaching...
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp


There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb

Spring approaching...
Re: ZX spectrum spider mod
I will put it down to the socket connection, for now. Will see if it reoccurs after a soak test.
Both issue 2 both ULA5C112E-3.
Swapped back and still working.
Will crack on with the spider mod as you suggested.
Thanks
Rob
Both issue 2 both ULA5C112E-3.
Swapped back and still working.
Will crack on with the spider mod as you suggested.
Thanks
Rob
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Re: ZX spectrum spider mod
Sorry to revive an old thread, I'm not able to send DMs yet.
I have acquired a 48K with a bad M1 line. To my amazement I've managed to de-solder the old chip, put in a socket and new z80. I've kept the spider in the same position (on top of the z80) but due to the socket it now sits a bit high and the case can't be fully closed.
I'm planning on moving the spider as you've suggested here, so thanks a lot for the images. I'm a complete novice here - how can I identify the collector side vs emitter side? Which one would have been originally connected to pin30 on the CPU? I'm also not 100% on the final image - 'TR6 collector to a +5V via, I can't quite make out where that is attached.
Any advice gratefully received!