Mac 128 and its external drive

[retrobecanes]

My Mac 128 reads 400K 3.5" floppy correctly from its internal drive.  My external 400K drive (M0130) reads and writes to disk perfectly well when connected to my Mac Plus.  However when I connect the external drive to the Mac 128, I get disk errors with the external drive: it will eject the disk immediately, it will load the disk but then display a system error (ID=02), or it will crash somewhere in the process.  This problem occurred all of a sudden, it was working fine yesterday.  Any idea as to what is going on there?

 

[retrobecanes]

Update: I am also using a Fanny Mac cooling system with this Mac 128.  I just realized that when I remove this Fanny Mac and connect the Mac 128 directly in the outlet, the problem goes away.  Could it have been due to power variations coming from the Fanny Mac?

 

[Johnnya101]

Yes, it is possible. I have a feeling the PSU might be on the way out if this is the case. It might need new caps. Have you opened it up to check?

 

[omidimo]

It could be the bourns filter. 

 

[tanaquil]

Could someone point me to a simple tutorial on how to diagnose/replace the bourns filter on a 128? I suspect it of being the cause of the problem I'm having with my 128, but I haven't had time to do a thorough investigation.

 

[Elfen]

Diagnosing a Bournes Filter can be easy or difficult, as it can he hidden by other issues and you can not know exactly until the filter is replaced and the problems disappears. There should be 2 Bournes Filters, but either one can effect the other drive or both drives. (I think there are 4 on the logic board as they are also used for the Keyboard/Mouse and Serial Ports as well.)

Problems associated with the Bournes Filter that could be other issues can be:

- Read Errors.

- Write Errors

- Boot Errors (see Read Errors)

Problems associated with the Bournes Filter:

- Not being able to go to proper tracks

- Not being able to get up to disc rotation speed.

  (Check the 5V line in the Floppy Port see if it at 5V or not.)

The Bournes Filter is that yellow chip by the floppy ports. It is a Resistor Pack Network. You should contact Uniserver, he has a few to sell and a 'generic' version that works well even though it is 1 pin smaller than the one on the board. He can give you the details on them.

Replacing it is not that hard but do take care in that the logic board can be damaged if you are rough in desoldering and soldering.

 

[retrobecanes]

Is Uniserver a user of this forum? I don't see him in the list of members.

 

[bse5150]

uniserver was banned.  you can reach him through his website http://maccaps.com

 

[tanaquil]

Thanks very much for the pointers. I was thinking about contacting Uniserver, but I thought I'd do a bit more troubleshooting first.

Another question (I hope this doesn't count as thread hijacking since it might be relevant to another user with 400K floppy drive problems): one of the issues with my 128 is that the internal floppy doesn't work at all. Cleaning will be my first step, but I am wondering if I could also test it by removing the internal 400K drive from the 128 and putting it in (say) a IIsi (IIsi because I have several and they are insanely easy to open). Is there any reason a healthy 400K drive would not work if hooked up to a IIsi motherboard/floppy cable? Would this fry something?

I do have an external 400K drive but am hesitant to open it to swap mechanisms unless I really have to.

 

[Elfen]

The SWIM in the IIsi does not handle a 400K Drive well. Any from a Mac Plus down will work fine as well as any 800K Mac SE with the IWM Chip Will.

The 400K Drive requires that the IWM Chip talking to it can adjust voltages to speed up or slow down the disc rotation. The SWIM can not do this as it provides a constant voltage for a constant speed in disc rotation.

 

[tanaquil]

Thank you!! That was just what I needed to know. I can use one of my SEs as a test machine. I just always seem to scratch my hands all to heck working inside compacts.

 

[retrobecanes]

Update on the Bourns filters: I was able to contact Uniserver and bought a kit.  I will see if that fixes the problem.  Thanks for the help and guidance.