Posted By
raze
on 2014-03-16
01:24:31
 |  1551 Drive
Is there a method to test whether, or not, it is actually the 6523A in the paddle that has failed?
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Posted By
gerliczer
on 2014-03-16
05:40:53
| Re: 1551 Drive
I don't know testing methods to check which part is failed except replacing the suspected component with ones known to be working. Or testing the suspect in a system known to be in good working order. But according to BSZ the usually failing device in the 1551 paddle is not the TIA but the FPLA. In the latest post on his blog - see here: http://hup.hu/node/130935 - there is described an FPLA replacement circuit made of 2 74 series logic ICs. It can be read here:http://bsz.amigaspirit.hu/Plus4/1551/Paddle1551FPLA.pdf. There is also the SuperPLA by Individual Computers which is a multipurpose replacement that can be used in five different systems including the 1551. So I would try and replace the FPLA first.
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Posted By
raze
on 2014-03-17
00:28:59
| Re: 1551 Drive
Thank you. Unfortunately Google translate makes reading/understanding quite difficult.
I do not have a working drive so I cannot swap components to see if they work or not.
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Posted By
gerliczer
on 2014-03-17
13:47:23
| Re: 1551 Drive
You're welcome. I don't think there is much to translate and understand. The link I gave to the FPLA replacement circuit should be self-explanatory.
Well, these beast are quite rare so it is not surprising that you don't have another one for testing. Good luck with the repair.
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Posted By
raze
on 2014-03-17
23:39:43
| Re: 1551 Drive
I get the general idea but there are two questions.
1. What is, and where does it come from, the O2 that is fed into pin 1 of the 74LS133?
2. What is, and where does it come from, the PC7/DAV that is fed into pin 12 of the 74LS86?
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Posted By
siz
on 2014-03-18
02:09:45
| Re: 1551 Drive
Ø2 is originally generated by the 1551 FPLA but it is also available from the computer on the expansion port. BSz used the expansion port one.
DAV comes from the drive (from a jumper) it controls the device number selection (8 or 9). 1551 maps to different memory addresses from the computer's side depending on the device number so this signal is required to decode the proper location.
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Posted By
raze
on 2014-03-18
19:48:21
| Re: 1551 Drive
Thank you.
1. Now that I have downloaded a clear schematic of the Plus 4 I can see that 02 is available on pin 24 of the expansion port.
This would mean that BSZ would have to run an additional wire between the computer and the drive? Not elegant but works ...
2. If I trace the schematic, PC7 (pin 32 on the mainboard 6525A) links to pin 19 of the paddle 6523. Correct?
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Posted By
raze
on 2014-03-18
20:21:19
| Re: 1551 Drive
I am confused. Why is the 02 needed? On the schematics of the paddle I have and those on the 'net make no reference to 02 into or out of the FPLA????????
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Posted By
raze
on 2014-03-19
00:40:11
| Re: 1551 Drive
I cannot make that link work.
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Posted By
siz
on 2014-03-19
02:10:12
| Re: 1551 Drive
It was a spam so probably it's better that you could not make it work. 
For your questions:
1. Devices should only drive the buses in the computer when they are allowed. Part of this "allowance" is a phase of Ø2. BSz mentioned that the 1551 paddle does not use this signal from the expansion port but generates it's own one internally in the FPLA and generates chip select to the 6523 that is in sync with the Ø2.
2. You are probably right but I did not check the schematics myself.
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Posted By
raze
on 2014-03-19
18:51:09
| Re: 1551 Drive
More confusion! If it is generated by the FPRA why is there an input to the IC 74LS133 on pin 1?
How did BSZ connect his PCB to the paddle PCB? I do not see any pins or wires in the photos.
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Posted By
raze
on 2014-03-20
02:12:55
| Re: 1551 Drive
I eventually found out that if the image was clicked it would enlarge. I get there eventually ..
On both drive schematics 02 is not shown although as stated above it is shown on the Plus 4 schematic. I get there eventually ...
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Posted By
raze
on 2014-03-30
01:05:38
| Re: 1551 Drive
I have been thinking - why was 02 (phi two) used necessitating another wire connection when there is 00 (phi zero) on pin 3 of the FPLA?
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