restoring a second OSI

dave
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Re: restoring a second OSI

Post by dave »

I moved my reply from the Files. . . Forum, since it's really more applicable here. That might give you a starting point

Also, if you try the obvious and are still stymied, then do you by any chance have BASIC in ROM available? Or, can you map an 8K block of RAM to A000? The reason I ask is, if you have it, you can write a little basic program to assert individual keyboard control lines while you check them with the logic probe or scope, then read back values while you press keys. You could either set up the program with the good keyboard, test it on the good keyboard, and then switch them out, or wire in the serial monitor to FF00, and run the basic through a hyperterminal/teraterm/puTTY/etc. Sometimes that approach is a quick way to narrow down a problem.

Sometimes, if I am working on an embedded system, I'll drop in a little interpreter of some kind, and exercise the various I/O lines remotely just the same way.

Best regards,

Dave
nama
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Re: restoring a second OSI

Post by nama »

Hi Dave,
Thanks for the tip. Unfortunately I don't have Basic in ROM. If you recall from another thread I have been trying to get Basic to load from the Serial port, but I need to get the SYN600 ROM to load to C/W/M menu before I can do that, and I was going to attack that project after finishing this one...maybe I should reverse the priorities.

I actually think I will next replace all the IC's in the keyboard section. I believe these consist of:

2 x BT26
2 x 74LS75
1 x 74LS04
1 x 74LS138

I'll let you know how I get on with that. If that doesn't fix it, the the problem must be in one of the diodes or resistors or even a bad socket.
Expect an update by tomorrow.

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
dave
Site Admin
Posts: 710
Joined: Tue Sep 09, 2008 5:24 am

Re: restoring a second OSI

Post by dave »

It's probably a good plan to just start replacing chips. Then, you can start putting chips back until it fails, to find out which one was bad. That way you also can reserve most of the new chips to fix something else.

You are right that it could be a socket problem. Even if it isn't you may want to invest in some low-cost ZIF sockets for this kind of application--it will save wear and tear, bent pins, etc. You could even solder in a machine-pin socket, drop the ZIF on top, and then you can easily replace the ZIF socket if it wears out.

Dave
dave
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Posts: 710
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Re: restoring a second OSI

Post by dave »

nama wrote:Hi Dave,
Thanks for the tip. Unfortunately I don't have Basic in ROM. If you recall from another thread I have been trying to get Basic to load from the Serial port, but I need to get the SYN600 ROM to load to C/W/M menu before I can do that, and I was going to attack that project after finishing this one...maybe I should reverse the priorities.
Yes, I asked in case you managed to get BASIC to load. Well, if you have 48K of RAM, then you can jumper the ROM for C/W/M (ROM block select jumper pin 3 to pin 10 instead of pin 3 to pin 7), then use the monitor to put BASIC at $A000, reset, and cold-start, and answer "memory size?" with something less than 40K, so BASIC's memory check doesn't stomp the interpreter. If you have less then 48K, then jumper the highest 8K block to address A000 (assuming a 527 card). I am pretty sure you can get the keyboard working without doing this, though.

Dave
nama
Posts: 357
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Re: restoring a second OSI

Post by nama »

I am very pleased to announce that the keyboard is fixed.
First I replaced all the IC's in the keyboard section with new ones. however that did not solve anything, which left me thinking that it must now be one of the other components. I broke out the multimeter and tested all the diodes and they all seems to check out ok, next I moved on to the resistors and I eventually found a pull up resistor that was rated at 4.7kohms but was measuring in the milli-ohms range (all other pull up resistors measured within range) so I thought I was onto something. I had previously suspected something wrong with the 'shift lock'. When I traced this pull up resistor back to C0, which is one of the lines from the 'shift lock', I was almost certain it was the issue. Out came my trusty soldering iron and I removed the offending part. I didn't have a 4.7k resistor, but I did have a 2k which I though would probably work as a pull up resistor, and I was right. The keyboard worked!!!!

So it may be a bit premature as I have yet to test every function of the machine including the floppy drive, and I'm missing an internal 40 pin ribbon connector from the CPU board to the A15 board, but I thought I'd list up the 'complete' fix anyway.

505b CPU board - reseat all socketed IC's brought it to life.
540 Video board - Replace 12mhz Xtal and replaced a dead 74LS163 @ U5E.
Power supply - Replaced a dead CA723CE regulator with an equivalent part.
Keyboard - replaced a dead 4.7kohm pull-up resistor on the C0 line.
Disk Drive - replaced two 4ZZ main bearings that were shagged.
Various - repaired many frayed and broken wires.

Finally, I really want to thank both Dave and Billdrom for all their help in getting this machine into a working state. I have really enjoyed this fix, and it ranks up there with one of the most satisfying I have ever done.

THANKS !!!!!

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
dave
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Posts: 710
Joined: Tue Sep 09, 2008 5:24 am

Re: restoring a second OSI

Post by dave »

Glad to hear it! I'm also glad you have documented it all here, for others to learn from. I am hoping the disk will work. Keep us all posted!

Dave
nama
Posts: 357
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Location: New Zealand
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Re: restoring a second OSI

Post by nama »

My disk drive has been plagued by very loud noises, vibrating, and rattling...really awful. I've pulled it apart 3 times now. Each time I power it up while it's apart and I never get any noises. Very smooth. I know it's not the bearings anymore, because I fixed that horrid grating noise by replacing the old bearings with new ones. The noise was driving me crazy. Finally today I have figured it out.
As most transformers do, it has a slight vibration. When the unit is assembled the transformer hangs upside down and in this position it must cause some form of simple harmonic motion, because it suddenly bursts into a very loud violent rattle and hum. Even a slight deviation from this vertically mounted position e.g. I tilt the unit slightly, the humming stops. Slight pressure applied to the transformer and the noise also stops.

I'm trying to think what would probably be the best way to fix this permanently. I'm thinking to unbolt the transformer, and put two washers as spacers underneath to that it's slightly elevated above the metal below, but still connected electrically (if incase it needs to be earthed to the case).

I'll let you know how it goes.

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
nama
Posts: 357
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: restoring a second OSI

Post by nama »

Yep, putting two thin washers under the transformer seems to have solved the noise issue.

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
nama
Posts: 357
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: restoring a second OSI

Post by nama »

I'm still having issues with this drive. I powered it up today to do some test in. I was trying to create a 65D disk via a serial connection as documented here:

http://osiweb.org/osiforum/viewtopic.php?f=5&t=66

Anyway, after a while the drive started slowing down and speeding up and slowing again, until it finally stopped. Again I pulled the unit apart. The main bearing a wheel still spins smoothly but now the motor had stopped and looked frozen. Anyway, I'm not one to be to afraid of pulling mechanical things apart as I can 'usually' put them back together again. I also found a page with some photos of internals of a similar unit from a tandon drive.

http://www.bobblick.com/techref/project ... motor.html

I pulled both the end caps of the motor and made sure I didn't loose the springs and brushes. Unfortunately I was not able to actually pull the main internals out for some reason as it seemed somehow locked in to place. I did a visual inspection and I couldn't see anything obviously wrong. I did apply a little bit of oil to the bearings though. I loosely held unit back together minus the springs and brushes and it seems to spin freely. Now I just have to figure out how to put the unit back together correctly with the springs and brushes inlace...sounds simple, but physically very very difficult...and fiddly. If I could figure out how to pull the unit fully apart, in a strange quirky way, this might actually make it easier to put back together. In the worst case, I may try to find a replacement motor.

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
nama
Posts: 357
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: restoring a second OSI

Post by nama »

As with everything related to this drive, I don't know if I've fix the problem permanently. I did manage to get the motor back together. After a bit of head scratching I struck upon a solution for getting the springs and brushes into place.
motor.jpg
motor.jpg (110.62 KiB) Viewed 15469 times
As you can maybe see from the photo there are two opposing 'tubes' that house the spring and brushes. The outer ends of these 'tube' are bent closed with a little tab. I ended up bending open these tabs, When theses tabs are open the end cap will not close as the tabs stick out preventing this. I held the entire unit together with rubber bands and tape and slid the brushes and springs in to the 'tubes' from the open tab end. Using tweezers to compress the springs, I then bent the tabs closed with a screwdriver. I did each side one at a time. Now with the tabs bent closed I was able to seal the unit up.

As I said, I don't know if I did anything special, but the motor spins again, and I am now letting it spin for a 'burn in' period. unfortunately the motor occasionally makes high pitched noises and seems to change speed briefly. So maybe it's not fixed fully. It could be time to source a new motor.

Phil

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
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