Search found 35 matches

by dizzy33
Thu Feb 27, 2020 9:26 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

Thanks a lot again Mark ! In the meantime "Bola_dor" helped me with the voltages measurements. They are all good. But now something new happens : running the same memory test now always end up with "IC25 failure" ... IC25 is a SN74LS157N which seems to be involved in the memory management. I am now ...
by dizzy33
Thu Feb 27, 2020 7:37 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

Thanks a lot Mark ! In the meantime "Bola_dor" helped me with the voltages measurements. They are all good. But now something new happens : running the same memory test now always end up with "IC25 failure" ... IC25 is a SN74LS157N which seems to be involved in the memory management. I am now trying...
by dizzy33
Thu Feb 27, 2020 3:33 pm
Forum: Hardware
Topic: ZX Spectrum+ video signal problem
Replies: 0
Views: 13

ZX Spectrum+ video signal problem

Hello, I own a ZX Spectrum+ which is working fine but it has a small video output problem : I did the composite mod on it, I don't know how was the picture before (never tried using the RF modulator), but the picture is a bit blurry compared to my ZX Spectrum issue 2 with composite mod, plus the col...
by dizzy33
Thu Feb 27, 2020 1:43 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

ZX Diagnostics reported bad IC's. I replaced all of them (all the 8 low RAM chips), but the problem remains : after one minute of use, my Speccy displays bugs. All RAM tests software say I have a problem with low RAM, but they never show the same IC's as defective ... So I am sure that a component o...
by dizzy33
Wed Feb 26, 2020 7:33 am
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

One thing you can do is check them one by one to see if there is a difference.. or With machine off measure resistance between equivalent pins in different IC.. you can do this in every pin NOT marked as A0 to A6.. How do I measure resistance ? My RAM chips are known working (and have been replaced...
by dizzy33
Tue Feb 25, 2020 9:38 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

To load the TZX I am using a Divmmc card.
by dizzy33
Tue Feb 25, 2020 7:42 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

About ZX Diags, I tested many versions, they all never show the same IC as bad ... I use the Smartcard V2 diagnostic, which does the same, it does not show the same low RAM IC as defective ... So it seems that a defective component on my motherboard does impact all the low RAM IC's . Yes I just chan...
by dizzy33
Tue Feb 25, 2020 6:29 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

OK so I took the measurements, here is the result (strange) : https://www.sinclairzxworld.com/download/file.php?id=3403 From the top view of the 4116 : For pin 1, +4,72v For pin 8, -12,25v For pin 16, 0v For pin 9, -5v Very very strange as if I follow the 4116 pinout found below (the same as the one...
by dizzy33
Tue Feb 25, 2020 5:57 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

Did you invert the +5V and +12V ? In the Mark post with the 4116 schematic and the Mark explanations they are inverted ...
by dizzy33
Tue Feb 25, 2020 5:53 pm
Forum: Hardware
Topic: ZX Spectrums problems : diagnostic software ?
Replies: 47
Views: 1765

Re: ZX Spectrums problems : diagnostic software ?

Thanks a lot for your explanations ! I will try it. As you said, the voltages should be fine, but what is strange in my case is that my Speccy works fine for 1 minute, then some bugs appear on the screen. About the ULA, I already replaced it with 2 other ULA's which are known to be working, but not ...