Hi
i cant find the failure of my spectrum 48k issue 4a, i thought it was ic6 or ic13 but the memory seem to have the right values. When i turn it on it shows:
A slightly larger image would have been useful. Does the Spectrum work apart from that odd initial display?
A number of faults could cause that, but I'll go for faulty upper RAM disrupting the initialisation.
Give the "Use a length of wire to briefly connect pin 5 of IC23 to 5V when you power on the Spectrum while it initialises (you can then remove it). This interferes with the generation of the /RAS signals for the upper RAM and so the ROM code will set-up the Spectrum to use only the lower 16K of RAM. The output of the voltage regulator or pin 14 of IC23 may be a convenient place to obtain 5V. Take great care not to let your jumper wire touch anything else." trick a go.
If that doesn't do anything, without some form of external test device, I'd try removing the upper RAM ICs.
As always, if the Spectrum has its original electrolytic capacitors, give it new ones. Failing capacitors can cause all sorts of odd symptoms.
A slightly larger image would have been useful. Does the Spectrum work apart from that odd initial display?
No. At the initial it was just one " 1982 Sinclair Re"; but after i made some mesures it makes two alternate with black screens.
I try it tomorow, thanks.
A faulty ULA is certainly possible, but is far from the most common fault.
I've got no idea what you meant when you said "now i mess up, it makes Always a NMI." We may be able to make more helpful suggestions if you can give a clear description of what you have done and what happened.
Comments
A number of faults could cause that, but I'll go for faulty upper RAM disrupting the initialisation.
Give the "Use a length of wire to briefly connect pin 5 of IC23 to 5V when you power on the Spectrum while it initialises (you can then remove it). This interferes with the generation of the /RAS signals for the upper RAM and so the ROM code will set-up the Spectrum to use only the lower 16K of RAM. The output of the voltage regulator or pin 14 of IC23 may be a convenient place to obtain 5V. Take great care not to let your jumper wire touch anything else." trick a go.
If that doesn't do anything, without some form of external test device, I'd try removing the upper RAM ICs.
As always, if the Spectrum has its original electrolytic capacitors, give it new ones. Failing capacitors can cause all sorts of odd symptoms.
No. At the initial it was just one " 1982 Sinclair Re"; but after i made some mesures it makes two alternate with black screens.
I try it tomorow, thanks.
schombi.de/my-retro-collection.html"
Thanks
I've got no idea what you meant when you said "now i mess up, it makes Always a NMI." We may be able to make more helpful suggestions if you can give a clear description of what you have done and what happened.
Assuming you have an issue 6A, what leads you to believe IC27 is faulty?