| Posted By
JamesC
on 2002-07-21
|  ARRGH 1551 problems (still)
Okay here's the stats on my 1551:
U2: MOS 6510T Date 4484
U3: MOS 6525A Date 3983
U4: MOS 318008-1 Date 0385
U5: Toshiba TMM2116AR-15 Date 8414HAK
U6: 4M1 HD61J215P
U7: MOS 251829-01 Date 54ZA
U8: EL74LS14 Date 8410
U9: EL7406 L4
OSC Crystal is KXO-01 16MHz Kyocera
Below OSC is a blank space on the motherboard illustrating where a chip might go
U11: 251853-01 QH800210
I have verified wiring against Jim's pictures on his wife's website. My particular 1551 does not have an optical sensor, but neither does Jim's 1541-C in the pale case. I have a 1541 Newtronics assembly with an optical sensor, like the 1541 assembly he uses with his 1551 board; both of these have serial codes starting with 50. The ones without optical sensors have serial codes starting in 40.
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Posted By
JamesC
on 2002-07-21
| continued
Current status of drive: I can read in a directory, but it hangs AFTER the blocks-free line. The red light is still on, the disk is turning. Turning off the drive is the only way to release the Plus/4 to get the READY prompt back. However if I turn the 1551 back on I get DEVICE NOT PRESENT error. I cannot RESET, I have to power both off and back on to get both to talk to each other again.
If I were to instead turn off the Plus/4, the 1551 gives me 4 quick blinks and then the red light stays off; however this is not consistent. Sometimes it doesn't blink at all, it just turns the red light off and stops spinning the disk.
If I hit RUN/STOP during the disk driectory display, I get the normal BREAK error but the 1551 refuses any future requests for disk access.
The drive speed adjustment is right on at 11:00 just like my 1541 and Jim's pictured 1541 drive mechanism.
If I instead try to load a file instead of the directory, it loads a bit and then stops spinning the disk. I can turn off the 1551 and regain control of the computer but I get a LOAD ERROR when this happens, and all I can LIST is the first line of the program.
Jim if I had your phone number I would have called you!
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Posted By
JamesC
on 2002-07-21
| Update
Jim, I swapped drive mechanisms so that the 1541 mechanism (with an optical sensor) was on the 1551 board. Not only did I get a corrupted directory but the whole mess smelled hot. (Okay I work with appliances and electronics for a living, so I can smell heat  )
The 1541 mechanism was a working mechanism before I put it on the 1551 board.
I put everything back and my 1551 still acts like I described above.
Examining the 1551 board, the three wires that wire back to the optical sensor (purple, white, blue) have no circuit traces from the connector to a chip on the board. They seem to go to ground.
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Posted By
JamesC
on 2002-07-21
| Hey Csabo
This was posted three times but at least the system gave me an error this time: Warning: Cannot add header information - headers already sent by (output started at /sites/emucamp.com/plus4/main.php:863) in /sites/emucamp.com/plus4/forumpost.php on line 77
It was actually posting but since I got an error instead, I kept retrying.....
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Posted By
JamesC
on 2002-07-21
| Another tidbit
If I power up both the 1551 and the Plus/4, then ?ds$, the 1551 hangs until I shut it off, and THEN I get "73, CBM DOS V2.6 TDISK,00,00".
This leads me to continue to believe that the problem is in the motherboard, not in the drive assembly.
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Posted By
BushRat
on 2002-07-22
| Okay
Sounds like you did, indeed, eliminate the mechanical side. The chip(s) that I would suppect is the 6526A(CIA) primarily, the 6510 (the CPU) second. The 6526 is VERY static sensitive. It was used on the C64/C64C to interface the joyports. Don't know how many I saw killed in our cold dry climate, here. They can also "lockup" and destroy themselves if a device is plugged/unplugged with the power on. They were of the old style, unbuffered, CMos design... which was both static and voltage sensitive. Some boards had the 6526 socketed, hopefully in your case, they are. I truly hated using my solder-sucker iron, even after all these years. I know what you mean about the hot smell, even though we lived in the bush, we had neighbors and a village within reasonable distance. Did consumer electronics repair, of and on, for nearly 25 years. Got out of the game when I needed magnifying type glasses to see the pathways. As you've noticed, the residual charge in those Commie supplies hangs on for a bit after you kill the power. Rule of thumb used to be to wait to the count of 10, before turning back on or unplugging joys, interfaces, modems. Saw a few Cmos kills, by folks being too quick on the trigger there.
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Posted By
BushRat
on 2002-07-22
| Hmmm...
Boy THAT was annoying... got the same error... double posted with only one click
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Posted By
JamesC
on 2002-07-22
| It's a 6525A
plain as day marked on the chip. U2, U3, and U4 are socketed, the rest are soldered direct to the board.
Could I use a 6526 in place of the 6525A? Your photo didn't give me enough detail to read the markings on your chips to verify part numbers against my own.
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Posted By
BushRat
on 2002-07-22
| Nope...
Has to be a 6526. I will have a 6526R4 and a 6526A-1 in the mail for you tomorrow.
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Posted By
BushRat
on 2002-07-22
| YIPS!
Sorry, James, ignore that last post!
Talk about brain burp... has to be the 6525... is what I meant, unless you can find a certified cross. I will have a 6525B in the mail in the morning.
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Posted By
BushRat
on 2002-07-22
| The difference
The 6526 was the CIA, the 6525 was a triport controller. The lockup could happen with ANY of the old Mos series chips. All were very static sensitive. The later generation chips had built-in diodes across the inputs to protect them from static and spikes better. Remember that Commodore had control of their own production on the larger chips. You can still find stocks of Commodore type chips, as they sold the 6502/6510 type CPUs to just about everyone making home computers at the time.
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