Error 01 means a ROM error. The ROMs of pluses can be defect. You can burn new ROMs with an eprom burner or you can buy them on ebay. There are a lot of people in this forum that can burn new ROMs.
Leaking caps can cause defect chips but you have to open the case to have a look inside.
Did the...
Perhaps a stupid question: Are you sure that you have a 1.4MB floppy drive? I own an SE/30 that had a 800KB drive, because it was an upgraded SE. What color has the cable of the drive? Grey/red or grey/yellow? What is the type number of the drive?
Did you clean the reading head of the floppy...
You do not have to buy new ROMs. You can test the ROMs by reading and comparing them with a burner with ROMs you can download from the net.
https://macintoshgarden.org/apps/macintosh-rom-archive
The plus had three versions of ROMs.
@demik Which Macrecorder did you build? Macrecorder or Macrecorder II? The Macrecorder II uses the TLC549 ADC. There is a schematic in the fall 1985 BMUG Newsletter.
You do not have to open the classic to measure the voltages. You can do it at the floppy port. The only things you need are a voltmeter and a little paperclip.
Did you measure the voltages at the floppy port?
There are a lot of parts on classic AB that can be defect. Most often: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40. Could be that you have to replace some of these.
Recapping AB and LB should be done. Take the battery out of th LB.
Thank you for all your feedback! First I tried pickitminus with my Pickit 3 and that worked! I could program the 1704.
The only problem is, that only some of my SD-cards could be used with the the sparkfun sd board. I knew about that problem, but had a little hope, that the 1704 could solve it...