1541 drive and faulty 6522 chip

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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

Yes as written in my first two posts I've also tried with the other device numbers for a floppy drive. Thanks.
I'll try swapping the 6522 with some coming from my Vic20s, good idea 8)
Cheers
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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

Hi, here's the update (I confess that, loving so much these old "machines", I feel like I should wear a spacesuit whenever I open and touch their electronics).

To make the story short: at last I found a socketed 6522, I swapped it with the other ones of the 1541, one at a time, trying all the combinations involving the chip coming from the Vic 20. Every time I also tried both connectors of the floppy drive. I issued the same commands as in the previous posts (i.e. LOAD"$",8 then using higher numbers up to all the "legal" ones for a floppy drive).

The problem remains exactly the same (I tried two known working machines: they can use perfectly a 1541-II that I also have): the Vic 20 replies "DEVICE NOT PRESENT ERROR". I even tried - adhering to the quote by Sherlock Holmes "when you have eliminated the impossible, whatever remains, however improbable, must be the truth" - also another new (and known as working) serial cable. Nothing changed in this case too.

:cry:

Thanks
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eslapion
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Re: 1541 drive and faulty 6522 chip

Post by eslapion »

@ldxstx
Do you have a good multimeter with continuity testing ?

If so, check the small inductors between the serial port connectors and the board elelctronics to see if one is damaged.

They are listed as LI3, LI4, LI5 and LI6 on the board.

The test you perform does not tell you if the problem is with mechanics or electronics. Why don't you just do a status check instead of a LOAD"$",8 after powering up the drive ?

If the status check works then it's a mechanical problem.
Be normal.
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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

Thanks eslapion for the suggestions!

I have the multimeter and it can check for continuity: I'll do this in the afternoon. Meanwhile I tried "the software way" and there are interesting news: as you said this time I also tried to check the status

Code: Select all

OPEN15,8,15
INPUT#15,N$,E$,T$,S$ 
at this point the prompt never comes back, so I don't even get to the point to print the info and close the channel.
Furthermore after pressing RUNSTOP+RESTORE to get back to the interpreter and then entering LOAD"$",8 the Vic shows "SEARCHING FOR $" and that's all; the same happens with "CLOSE15" as an alternative.
According to Ray Carlsen it could be UB1 and/or UC3, isn't it? I would discard the other chips since I can see the red led on each time the computer resets and during this operation the motor spins just for a couple of seconds and then it stops. Moreover when the apparent freezing starts and I type LOAD"*",8 the motor _doesn't spin at all_ and the red led stays _off_ (i.e. no tangible signs of a response coming from the serial bus).
If you have any inputs in the meantime, otherwise I'll be back after checking the inductors too. We are making progress anyway :)
Thanks!

(EDIT: after the tests made by swapping the 6522 taken from the working Vic 20, could we restrict the culprit just to UB1?)
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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

eslapion wrote:@ldxstx
Do you have a good multimeter with continuity testing ?

If so, check the small inductors between the serial port connectors and the board elelctronics to see if one is damaged.

They are listed as LI3, LI4, LI5 and LI6 on the board.
I tested all of them and they all work as expected, so as written above maybe it's the UB1 chip...

Thanks for your input :)
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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

Hi, here are some news for completeness:

reading again the posts I realized that I didn't check the weldings as suggested by MCes, so I removed the board and did it (there are no signs of alterations). At that point I thought "ok you wanted the bicycle, then ride the bicycle": I wanted to complete what was remaining and check UB1.
I took a logic probe (it could be helpful in the future) and this datasheet http://www.ti.com/lit/ds/symlink/sn7406.pdf, then connected the probe and followed the electric diagram (in the service manual MCes previously posted about). I wrote a simple Basic program to deal with the commands to the drive while I was keeping the eyes on the probe.

I found these abnormal values:

just after connecting the drive to the Vic 20:
3A neither high nor low
3Y low

after the OPEN and the INPUT#:
6A low
6Y low

I think that now I will check the other chips as well. Electronics gurus if you have some hints you are _always_ welcome!! :)

Enrico
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Re: 1541 drive and faulty 6522 chip

Post by DrVeryEvil »

From all I'm reading, I am surprised nobody has looked at the roms. If it starts ok when it's turned on, then I might lean towards the rom that is lower in memory first.
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MCes
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Re: 1541 drive and faulty 6522 chip

Post by MCes »

Hi,
for simplicity: it's better to indicate the pin number where you measure the voltage.
More than 2V is High, but a good "1" level will be more than 3V.
Remember that 7406 is "open collector" NOT gate, so the only measure that you can't find (or it is broken) is: input "1" output "1", otherwise the measure can't tell anything.
Remember that metallic support/shield isn't the 0V (GND) of the board, but the 220V line GROUND, so manipulate the hardware with 220V line cable fitted will be an electrostatic risk that can damage some chips (6522, ecc...).
I suggest to de-solder two chips: 7406 and 74LS14, put 2 sockets and try with new chips: the job of "socketting " will be useful in future if will be a new damage on this serial line drivers

NOTE:
The 74LS86 hasn't pins directly connected at serial port connector, so it's rare that it is damaged from electric potentials injected through the serial cable
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." (Albert Einstein)
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MCes
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Re: 1541 drive and faulty 6522 chip

Post by MCes »

DrVeryEvil wrote:From all I'm reading, I am surprised nobody has looked at the roms. If it starts ok when it's turned on, then I might lean towards the rom that is lower in memory first.
If I remember well the firmware check the ROM and if they have problem (checksum error) the red led continuously flash,
if the problem is strong the red led remain "on", and the motor remain in rotation
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." (Albert Einstein)
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ldxstx
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Re: 1541 drive and faulty 6522 chip

Post by ldxstx »

Hi, pins are respectively 5-6 and 12-13. Thanks for the tip.
MCes wrote:Hi,
More than 2V is High, but a good "1" level will be more than 3V.
Remember that 7406 is "open collector" NOT gate, so the only measure that you can't find (or it is broken) is: input "1" output "1", otherwise the measure can't tell anything.
I looked at the logic diagram on page 2 of the datasheet; interesting how in this case it seems as insufficient. :shock: :!: Always something to learn, fascinating. EDIT: after some research I think I understand what you meant.
MCes wrote:Remember that metallic support/shield isn't the 0V (GND) of the board, but the 220V line GROUND, so manipulate the hardware with 220V line cable fitted will be an electrostatic risk that can damage some chips (6522, ecc...).
Thanks. I placed the alligator clips at the outs of the rectifier bridge CR1 ("+" and "-"), so not on ground.
MCes wrote:I suggest to de-solder two chips: 7406 and 74LS14, put 2 sockets and try with new chips: the job of "socketting " will be useful in future if will be a new damage on this serial line drivers

NOTE:
The 74LS86 hasn't pins directly connected at serial port connector, so it's rare that it is damaged from electric potentials injected through the serial cable
Ok MCes I'll send you a PM, thanks for all your inputs so far!

And of course to all the others as well!

:)
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eslapion
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Re: 1541 drive and faulty 6522 chip

Post by eslapion »

MCes wrote:
DrVeryEvil wrote:From all I'm reading, I am surprised nobody has looked at the roms. If it starts ok when it's turned on, then I might lean towards the rom that is lower in memory first.
If I remember well the firmware check the ROM and if they have problem (checksum error) the red led continuously flash,
if the problem is strong the red led remain "on", and the motor remain in rotation
Correct. RAM and ROM problems cause a flash sequence on the activity LED.
Be normal.
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