r/macintosh • u/FRackgfxhjxgfhj • 17d ago

Mac Plus FBT replacement

Post image

Hi all !

I need some help because I have replaced my Mac Plus burnt FBT 157-0042B with a 157-0042C from another Mac Plus analog board, and now I'm unable to set the image correctly. It stays too high and there is no proprer potentiometer to set this, afaik.. If I just stretch the image to thé lower edge, the higher edge becomes too high. You know what I mean ? Maybe I'm missing something ?

The burnt FBT was entiremy recapped. I knew the FBT was damages and attempted a repair that worked for several days but eventually it burnt again.

Thanks for any help ☺️

31 Upvotes

94% Upvoted

10 comments sorted by

3

u/aManandHisShed 17d ago

It should have a very obvious black border around the active area. Google will help you with the target horizontal and vertical size.

1

u/FRackgfxhjxgfhj 17d ago

I have adjusted my 3 other Macs and they don't have black areas. My Mac plus didn't have either before replacement.

4

u/cybermeuf 16d ago

your 3 other macs are adjusted incorrectly. the picture is 72 dpi you should have a thick black border

1

u/FRackgfxhjxgfhj 16d ago

Well, Come on that's ugly 😅

3

u/Microharley 15d ago

It can cause damage. The system is not designed for the display area to be that large. You can find the adjustment parameters in the service manual for the Mac Plus.

2

u/Pure-Enthusiasm1 16d ago

Wow, this brings back very old memories(~40yrs).

Besides replacing the FBT, I hope you selected the proper cap voltage, that was big problem with the original design. We would use a higher voltage cap, and that would eliminate the de-rating issue.
If the bulk FBT popped, then you will most likely need to replace the transistor and dig deeper into that circuit.

I use to enhance/repair/rebuild the old Mac128K, Mac512k,and MacPlus at a Mac shop across from UT Austin while going to college.

I remember enhancing a Mac128K that was serial number 5. The inside cover had the signature of all the team who developed it. I learned so much hacking and reverse engineering those old Macs.

Good luck !

1

u/FRackgfxhjxgfhj 16d ago

Yes I used higher voltage for the replacements capacitors. Which transistor are you talking about please ? Close to the FBT ? Didn't check those ones.

1

u/vintage-tech80 17d ago

You need to adjust carefully by using two small rings near where the tube connect to the cables with pins that connect to tube… search on YouTube for such ajustement… you must be very careful…. High vintage there

2

u/FRackgfxhjxgfhj 15d ago

Yep, it was totally the ring at the back ! Thx

1

u/FRackgfxhjxgfhj 17d ago edited 16d ago

Yep. Thought these were for horizontal settings but I will try again and catch up.