I had the same problem on a Pfaff 1475 CD. Machine not coming "up" until 2nd or 3rd attempt.
The root cause was a defective 22uF electrolytic decoupling capacitor next to the L387A voltage regulator on the main PCB, causing the L387A to constantly reset the CPU. The simplest fix is simply to solder a new 47uF capacitor directly on the wires of the old one. That should keep it going for years.
I got the hint from the L387A datasheet recommending a 100uF decoupling capacitor.
The fix is easy and inexpensive, and I hope this will help anyone with this otherwise great machine.
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Hi Mr. Kaur,
I hope you were able to fix your PFAFF 1475 CD machine. If you have't do ne yet and still want to do it, I could help you out. I have the same machine and can fix your mother board or I can provide you with a repaired one if you like.
Message me now either here or contact me via email stelitex at y a h o o d o t c o m.
. whilst the 1475 is a great machine, it is getting on in years, and unfortunately, you may be experiencing the early stages of 'computer' / pc board failing. A trip to the technician may be you best option. If it is the pc board, sit down before asking the cost to repair it :)
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These instructions apply to PFAFF 1475 CD. They may also work for other machines.
If you have some advanced electronic repair skills and tools, check the following:
For 220 Volts models - there is a fuse next to the power input, make sure it is good. There is no such a fuse for 120 Volts model.
If the fuse is Okay, you have to get access to the main circuit board by removing the bottom cover.
Check the primary on the transformer for 120 V AC (220 V AC respectively). Check the secondary side for 5 V AC (luminescent display), 9 V AC (turns to 5 V DC by rectifier, 4700 micro farads capacitor and a 5 V regulator STI L387A) and 28 V AC (turns to 35 V DC by rectifier and 2200 micro farads capacitor.
Pay attention to two soldered round fuses in series with the secondary 9 V and 28 V - both should be good. On the big capacitors you should have 9 V DC and 35 V DC.
Common symptoms for bad small 22 micro farads capacitors next to the some of the IC's - there are 5 of these: These capacitors are in parallel with 5 V DC.
## All of the LEDs light up but the display is blank
## All of the LEDs light up, the display is blank, and after a minute no LEDs at all
## No LEDs nor display.
Replace ALL five 22 micro farads capacitors using a good desoldering pump or desoldering station!.
Enjoy your resurrected PFAFF 1475 CD machine!!!
I just did this procedure on my aunt's one (Made in West Germany around 1990).
The typical rebuild on this board is done by replacing the 22 micor farrad caps. There are 3 or 5 of them depending if it is new or old style. Note: the power to the sew lamp goes straight from the motor to the lamp, the power to the control panel goes from the motor to the main board (base plate) then to the control panel. If you get the LED's on occasion then it is not the transformer or fuses in the base plate but simply the caps. Sometimes you can just scrape off the electrolytic gel that has oozed out of the caps off of their teminals, but replacing them is the best. A Pfaff dealer can get a core credit for your board if you take it in. You shouldn't have to pay more than $200-$300 for a rebuilt base plate.