The new keyboard membrane arrived from the UK. I replaced the membrane and it worked perfectly.
I also replaced the 7805 5v power regulator with a TSR 1-2450 switched regulator. This one does not produce any heat, så the temperature inside the Spectrum should now be very much cooler.
I also hooked up the Interface One adapter that allows connecting a microdrive.
And on the rear of the Interface One i connected the Multiface One, that allows saving programs to microdrive or tape. It also allows to pause a game and enter a poke that for example gives endless lives in a game. 🙂
Tested it all, and it works as designed. Perfect, next project… 🙂
I got the capacitors in the mail, and replaced them all.
Apparently, the positive end of the C46 capacitor was wrongly marked on the circuit board. I documented the capacitors on this issue two motherboard, for future use. 🙂
When tested, the image still had that yellowish tone, so it was time to adjust VR1 and VR2.
I used my oscilloscope attached to the composite wire to get the noice level as small as possible.
Much better, now it is white as it should be. 🙂
Can’t test anything else right now, because i am waiting for the new keyboard membrane from UK to arrive.
This is a Sinclair ZX Spectrum 48k home computer released in 1982.
I bought this one new in the mid 80’s. (This is an issue two.) When i upgraded to a C64 i sold it to one of my cousins. I got it back a couple of years later when my cousin was not using it anymore. Then it has been in storage ever since.
It is booting, but with a distorted image. It only has RF output via an RCA on the backside. But since i want to use composite video, i will have to do a mod. 🙂
The keyboard membrane connectors were bad, so i could not try anything else but to power it up. (I have ordered a new membrane from the UK, and i will replace it when it arrives.)
All the capacitors will be replaced as well. (Same here, had to order some and will replace them later.)
I did the composite mod and tried it on my monitor. Much better, but with a yellowish tone. I will adjust the VR1/VR2 when the caps have been replaced to see if this will fix it.
This is a Texas TI-99/4A home computer released in 1981. I have had this one for like twenty years or so, but never used it. (Got it from a friend that never used it either. 🙂 )
It is working, but just had RF output via an external RF box. (It uses a 6-pin DIN that puts out component video, Red, Green and Blue.)
But since i want to use composite video, i had to do a mod. 🙂
There is a mod for the external PAL RF modulator, model PHA 2036. It makes it possible to add one composite RCA connector and an audio RCA connector.
It was an easy mod, i just drilled two holes for the RCA’s and soldered three wires. 🙂 The description of the mod said nothing about insulating the RCA’s from ground though. After beeping out ground vs video ground, i noticed that they were not connected. If i just mounted the RCA’s as they were, the ground and video ground would be connected. So, i isolated the RCA’s from ground with some electrical tape, just to be sure.
After this, the composite video worked, but i still have to see if the audio works. I have never used a TI-99/4A before, so i have to figure out how to get it to produce sound. 🙂
Next step will be to try to get it connected to my PC to see if i can get it to load a program. 🙂
With a switch mounted, so i can change back to the Kernal ROM i had in the machine before, if i would need it in the future.
I also changed the LED from red to blue, and changed the capacitors, if you with keen eyes noticed that on the picture and remembered the picture from the previous post. 🙂
I did a simple speed comparison between an original C64, a C64 with JiffyDOS and when using a Final Cartridge III :
My test file uses 92 blocks on the disk.
Original C64 : 57 seconds.
With JiffyDOS : 9 seconds.
Final Cartridge III : 6.5 seconds.
As you can see, the Final cartridge III is the fastest one when only looking at loading times, so JiffDos is not really necessary if you use this type of cartridge and just loads games. (If i did these tests correctly…. 🙂 )
If you Google JiffyDOS you can easily find an authorized sales channel for JiffyDOS. I bought my firmware from one of those. (A Kernal ROM file) (And i have an order confirmation email and an order ID to prove it if necessary. 🙂 )
It is also available as a chip-for-chip replacement ROM, so you just have to swap the old chip for the new one, for those of you that want the job done quickly. 🙂 Remember that you would have to buy one for your diskdrive too… 🙂
Since one of my Philips CM-8833-II monitors now has S-Video input, all i needed now was an S-Video cable for my C64. After assembly, together with a 300 ohm resistor for the chrominance, this cable is now done! And tested with flying colors. 🙂
This is a Commodore 64 (C64) home computer made in 1984. (The C64 was released in 1982.)
This one is going to be my “daily driver”, and need to get some modifications done. 🙂
I am planning to install JiffyDos that speeds up the access to the 1541 diskdrive. JiffyDos roms are still available for purchase through legal sources. (A link to the site will come in a future post.)
I am also thinking of removing the RF-modulator to get a clean S-video ouput with less interference.
Nu har det varit några dagar med diverse småpysslande som inte riktigt är värt att ta upp, såsom lite spelande på C64:an/PC:n samt lite labbande med en uIEC/SD till C64:an.
(Ett SD-kort monterat på en adapter som kopplas in i serieporten på C64:an och emulerar en diskettstation.)
Annars blev det idag mestadels avlödningar av komponenter från en skrotad C64c.
De kommer att bli reservdelar som kan plockas fram vid framtida behov. 🙂
Har även plockat fram en C64 av den första modellen, (den s.k. “brödburken”), som jag ocksÃ¥ kommer att ha i “skarp drift”. 🙂
För tillfället är den dock trasig, då den bara ger en svart bild vid igångsättning, men det kommer att ordna sig.
När jag ändå hade avlödningsutrustningen framme så passade jag på att löda bort 4 st kretsar från den, som ofta kan generera felet med svart skärm, och montera socklar för dessa istället.
Det gör ju att det blir enklare att felsöka i framtiden, då det bara är att byta komponenter och se om den startar.. 🙂
Om det inte räcker med dessa 4 sÃ¥ löder jag bort CPU:n med, och socklar även den…
Nu j-lar i mig blev det modding av en gammal C64c! 🙂
DÃ¥ jag har flera dylika i samlingen, sÃ¥ tog jag den som sÃ¥g sämst ut, och moddade lite…
Den skall bli den 64:a som jag skall ha framme och använda i hobbyrummet när det blir klart.
Monterade isär den, gjorde rent plastskalen, och grundlackade samt lackade med hobbyfärg.
Nyansen är “lite lätt strypt smurf”, kan man säga… 🙂
Mörkare blå än en smurf alltså. 🙂
Bytte ut lysdioden som indikerar att 64:an är på, (Powerlampan alltså, lite snabbare sagt. 🙂 ), till en rund blå med kromad ring runt, istället för en rektangulär röd.
Har tidigare lött in ett större EPROM i datorn, med tillhörande switch, så jag kan välja mellan några olika Kernels.
Just nu har jag tre att välja mellan.
Standard engelsk ROM, svensk ROM, och “JiffyDos”.
JiffyDos har de gjort om lite kan man säga, så diskaccessen går mycket snabbare än original.
Lite kortare tid att vänta på att bl.a. spel laddas alltså. 🙂
För att det skall fungera, krävs dock att diskdrive också är försedd med ett JiffyDos, så jag fick modifiera en av mina 1541-II:or med en switch och original/JiffyDoslägen att välja på. 🙂
Knappen på C64:an kan ses på bilden högst upp till vänster.
(Vänsterläge, mittenläge och högerläge är alltså möjligt.)
