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Post by designcraft on Mar 30, 2016 9:32:58 GMT
yeah, thanks! You know, i had a very bad feeling when i bought this C128 DCR and it arrived with a non working drive. I was disappointed... I start to collect Commodore stuff this year, and i have some background in electronics (hobby level), but i really like to repair these machines. It's very good when something working again. I have a few 45ns W27C512 EEPROM now, so i will try to replace the bad PLA in one of my C64, so this will be the next step.
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Post by designcraft on Mar 28, 2016 19:32:27 GMT
Thanks very much! I have a few C64 too, I dismantled and cleaned all. I have 6 now... Can I call it Commodore fewer?! One of the breadbin had a problem (the switch was bad... but i soldered it until i can replace that). After power on the characters appeared in rainbow color, so i checked the color sram, but that was good, so i changed the PLA, and now it's working too. I need a new PLA now, but until that i experiment with an EPROM based solution. I'm using uno2iec (arduino based drive emulator) to connect my C's to the PC, i want to improve that with an sdcard, and i want to make some custom cartridges to experiment. I will try to make music with the SID, so that will be my next project (analog synth with SID, and so on), so i have a few idea.
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Post by designcraft on Mar 24, 2016 0:28:01 GMT
The disk Id error is solved too. I measured the signal from the write protect sensor to the 74LS14 inverter and found it to be good. solution: I half-cut one trace on the pcb when socketed the 7406 IC... found it after I followed the sensor path from the 7414 pin 10 to the 65c22 pin 39. A thin wire soldered between the two pin and voila! Everything is in working order! Not beautiful but good enough... One happy C128 DCR owner.
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Post by designcraft on Mar 23, 2016 17:33:33 GMT
I made it!!! After countless hours and swapped ICs, the drive is working again... or first time really. I desoldered and socketed numerous chips... What i replaced: 7414, 7406 (x2) chips, socketed and swapped the two 65c22 VIA, and checked the two 6526 VIA, but these cannot checked with the piggybacking technique! So I read and read more troubleshooting tutorials and I read the SAMS book for C128DCR and one thing was important: 7. Serial Port Serial Port (CN6) works only with peripherals that work In Slow mode (like Commodore 1541 Disk Drive), does not work In Fast mode (with 1571 Disk Drive). Check CIA1 IC U1. So I socketed that 6526A CIA, and the drive works again in C128 mode too!!! Whoa... One problem remains after all, and this is a disk ID error. When I change disks there is no motor sound, so the sensor isn't working. No motor sound too when I first insert a diskette. I see that sensor, and i made some photos of it with my phone camera (the camera sensor is see the IR light from the led), and there is IR light, so maybe another IC is the problem?... Thanks very much for the help for all.
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Post by designcraft on Mar 18, 2016 11:02:40 GMT
I tried in C64 mode: wrote a BASIC prg to fill up space with a seq file, and it is working. Saved and can read after from both sides in c64 mode.
I also tried piggyback some IC-s at the serial port, to find faulty logic ic-s.
When I at the 74LS14 (U16), I got the DIRECTORY command, and load"$" working in C128 mode!
BUT just exactly one substitute ic works, if i try another sn7414 form a batch than not working again... So maybe the piggybacked plus ic is faulty and that disabled the fast serial mode?
Interesting, the drive work in 1541 mode (with plus ic at sn7414) at power on. When i list the directory, i get 0 block free, but now i can do "u0>m1" and that way i can see the whole disk, and can load data from both sides! By the way, the operation not so fast, so i think that it work in double sided mode, but not with fast serial.
The question is: what should I do now?.. How can I repair the fast serial mode, or how can i let the hardware start in 1541 mode in C128?
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Post by designcraft on Mar 15, 2016 23:56:19 GMT
Wow, thanks donno128, this is really interesting... Maybe that's the problem. The burst mode serial function is in the MOS 5710 IC which is a gate array... combined floppy controller, and CIA.
from the wiki: "Commodore embedded reduced (just 4 registers) CIA-like logic for the cost reduced Commodore 1571 inside the C128DCR (See Commodore 128) in a gate array called 5710 which also contains other functions. The 5710 CIA has the serial clock for the fast serial interface hardwired to a CIA6526 equivalent Timer A value of 5, leading to a per-bit time of 5µs on transmission. This is different from what used to be a Timer A value of 6 in the 6526 CIA in the original Commodore 1571. The 5710 CIA does not contain timer or timer control registers. It only contains two port registers and the register to control the serial shifter and its event."
So, can I switch off the fast serial burst mode in a c128dcr, from software, or hardware? How can I test this theory? Sadly I can't find any 5710 replacement chip on the market...
The problem is that now i can't use the drive in c128 mode with single sided (1541) mode for testing, i can't do "u0>m0", probably can't communicate with the drive because the wrong serial connection...
The serial comm speed is dependent from the 16MHz crystal, should I check out that too? The crystal is able to go wrong?
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Post by designcraft on Mar 7, 2016 10:19:29 GMT
Read all the ROMs, C128 Basic and 1571 dos rom, and all is identical to downloaded .bin files...
So, I don't understand. PLA, or SRAM? These are all vulnerable, so maybe these are the next, but i don't understand how this cause the working drive in C64 mode...
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Post by designcraft on Mar 6, 2016 21:32:33 GMT
I built a ROM reader with an Arduino and read the 318077-01 rom, and compared to the BIN file of the same rom downloaded from internet. This rom layout is: C64 BASIC, C64 KERNAL, C128 editor, Z80 BIOS and C128 KERNAL. So far so good, my rom is OK, every byte matches.
But the c128 basic is in another rom, so i will check that, and the drive rom's too...
"hopefully" i will find some mismatch. I don't think any other way that is made the drive works in C64 but not in C128...
Any idea?
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Post by designcraft on Mar 3, 2016 19:37:57 GMT
Yes, so I suspect the c128 ROM, because in c64 mode everything is working. The only one chip what is different is the rom, the floppy ic's are the same too in both modes. Or not?...
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Post by designcraft on Mar 2, 2016 22:33:52 GMT
Strange, but mine is doing the same sometimes in c128 mode, so no ready prompt after the copyright text on top of the screen when the machine started... Are you tested yours in C64 mode? If yes, what happened there?
I don't understand this c64 OK, C128 fault issue...
thank you!
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