Repairing a Disciple disk interface - info for others
Just posted this on my weblog, but I think it's also interesting to put here.
This week I did some work on a Disciple disk interface which I got from Ruud Baltissen on the last retro computer fair in Maarssen.
It caused a ZX Spectrum not to boot, with garbage on screen etc.
Using GAL's instead of PAL's in the Disciple
I immediately suspected a PAL chip to be the problem.
I know from the past these died quickly in a Disciple interface, and being very expensive: MGT enabled security on the PAL chips so it was not possible to read the contents and clone them back then.
Fortunately someone once received a repaired Disciple interface with PAL chips that did not have that security, and he was able to read the contents and publish it on the net.
There is no legal limit anymore because MGT does not exist anymore, so I can happily download the PAL files.
I do not have PAL chips in stock; they're obsolete and should be replaced with GAL chips.
But the files I downloaded were not compatible with the GAL chips.
I needed to translate them.
For this, Lattice, the creators and manufacturer of PAL and GAL chips, publiced a GAL to PAL translator.
This command line utility will convert a PAL jedec file to a GAL jedec file.
I downloaded the utility, converted the PAL20L8 files, and tried to program a GAL20V8 chip with the new files.
Then I replaced the PAL chips on the Disciple, and it works!!!
So the Disciple boots again, and everything seemed fine, except for the 7805 voltage regulator on the Disciple, which is overheating.
I replaced the 7805, but it still get's to hot, possibly causing instability.
I am currently adding new cooling paste, and replacing the cpacitor at the 7805.
Hope that will solve all problems.
-Update-
Bad soldering contacts on Disciple
I suspected the inhibit and nmi buttons to have problems due to aging, so I measured the resistance: I found values of about 30 ohms.
I desoldered the switches, and measured again: no problems with high impedances.
So the conclusion is: the soldering contacts are bad.
I resoldered all important contacts on the Disciple board: all chips and more.
Now all problems seem to have gone.
So 20 - 25 years of aging of these Disciple interfaces seem to give result in bad soldering contacts! Just to let you know!
This week I did some work on a Disciple disk interface which I got from Ruud Baltissen on the last retro computer fair in Maarssen.
It caused a ZX Spectrum not to boot, with garbage on screen etc.
Using GAL's instead of PAL's in the Disciple
I immediately suspected a PAL chip to be the problem.
I know from the past these died quickly in a Disciple interface, and being very expensive: MGT enabled security on the PAL chips so it was not possible to read the contents and clone them back then.
Fortunately someone once received a repaired Disciple interface with PAL chips that did not have that security, and he was able to read the contents and publish it on the net.
There is no legal limit anymore because MGT does not exist anymore, so I can happily download the PAL files.
I do not have PAL chips in stock; they're obsolete and should be replaced with GAL chips.
But the files I downloaded were not compatible with the GAL chips.
I needed to translate them.
For this, Lattice, the creators and manufacturer of PAL and GAL chips, publiced a GAL to PAL translator.
This command line utility will convert a PAL jedec file to a GAL jedec file.
I downloaded the utility, converted the PAL20L8 files, and tried to program a GAL20V8 chip with the new files.
Then I replaced the PAL chips on the Disciple, and it works!!!
So the Disciple boots again, and everything seemed fine, except for the 7805 voltage regulator on the Disciple, which is overheating.
I replaced the 7805, but it still get's to hot, possibly causing instability.
I am currently adding new cooling paste, and replacing the cpacitor at the 7805.
Hope that will solve all problems.
-Update-
Bad soldering contacts on Disciple
I suspected the inhibit and nmi buttons to have problems due to aging, so I measured the resistance: I found values of about 30 ohms.
I desoldered the switches, and measured again: no problems with high impedances.
So the conclusion is: the soldering contacts are bad.
I resoldered all important contacts on the Disciple board: all chips and more.
Now all problems seem to have gone.
So 20 - 25 years of aging of these Disciple interfaces seem to give result in bad soldering contacts! Just to let you know!
Post edited by bverstee on
Comments
I remember mentioning the '7805 getting hot problem' in one of my letters being published in the good old 'Format - The home of z80 magazine'. I believe that the addition of a passive heatsink will solve the instability problems that are present mainly (from my experience) on 128K machines.