What's new
What's new

Deckel FP5NC 5v Power Supply issues

Parkerbender

Stainless
Joined
Dec 19, 2009
Location
Kansas City Mo, USA
Hi Guys,
I am trying to fire up an old Deckel FP5NC before hopefully finding it a new home, and I am having an issue with it letting the smoke out of a resistor on (what I think is the) 5vdc power supply board. I have replaced it once, with a 100 ohm resistor as it appears to be indicated as in the book I have for it, but just as soon as I flip the switch, it smokes it again. Everything I can find says it wants 380 to the machine, which I managed to get almost exactly with a multitap transformer and some buck/boosts.

I don't *think* that it has the option to be setup for 208/240, but if I am wrong, PLEASE let me know! Also, there's no way that having the phase rotation backwards can do that, is there? And lastly, I have 3 hot wires and a ground in my shop. I tied the neutral to the ground in the machine where the wires come in. I get 220 between L2 and the neutral, so I am good there, correct?

Does anyone have any ideas on this guy? Such a sweet old machine, I really want to see it go on the live in someone's shop as a bragging piece, and not end up as parts or something...

I have pictures of the offender, as far as I can tell that's the only thing keeping it from being alive, if I just knew why it keeps frying...

-Parker

EDIT:
Upon hunting, I have found that Rider-83 had this exact problem back in 2006, and replaced r29 (the one that has been smoking) and C11 (which upon further inspection looks like it could be bad as well)... I am going to swap them both out and try it again, but I would sure be interested if anyone has any idea why they might be burning out, or if it could just be a getting old thing?

IMG_20210127_144349.jpgIMG_20210127_144337.jpgIMG_20210127_144325.jpg
 
unfortunately the circuit diagram in 1st photo is not readable, PM forum doesn't support large image hosting, try to find a place to upload high resolution image with a readable diagram and post a link here, then we can look at what that resistor does to try and figure out what might be wrong
 
I wanted to echo that last comment. Please post a readable version of the circuit diagram and we can help you with it. Are R28/C11 at the top left of the diagram? If so, probably something downstream from the board is drawing too much current, and this is a "sacrificial" resistor. But I may be looking at the wrong R/C pair, since I can't read the schematic.
 
Facebook

photo


10106068724998423


143501251_10106068724185053_3049239849466347160_o.jpg


Ok, let's see if this works...

R29 is in the top right(right middle right) of the schematic, C11 is between it and R30 and down. It appears that if C11 failed shorted (which I thought caps failed open, but, what do I know...) I think that would make it the easiest path from C11 to what I think is the ground plane shown as pins 5,6,7,8 on the top left.

Thanks guys!
 
I downloaded the photo onto my desktop, R29/C11 are part of the voltage divider at the input for the triple op amp in the top right.

I guess C11 is shorted. That means that R29 gets 5V across it, which means that it dissipates V^2/R = 1/4 Watt. If it's a small resistor (1/10 Watt) that will burn it out.

Replace C11 and R29, that may fix the problem.
 
C11 looks to be the "brown" tantalum in one of the pics in the first post, below the other tantalum, and it is typical for them to short out on failure, they are sensitive to reverse polarity

that opamp seems to be a some sort of over/under voltage check circuit that sends the signal down to the IC5 (PB3, CB1) and lights up D10 in case of something - had you posted a picture with readable nominals, we could figure what the correct operation and input/output states are, but that slightly better resolution pic is still unreadable, and I don't know what is the source for the input on the 5-6-7-8 pins is to tell more about it, hence difficult to suggest what made the cap fail, these pill type tantalums generally are quite reliable
 
C11 does look very suspicious. Old Tantalum caps can be really nasty and when they fail short they can take other components with them. Nasty in more ways than one - when they fail they make a really horrible smell. If it has failed recently you may still be able to smell it. Have a good (cautious) sniff. If you desolder it you can check it with a capacitor tester. Probably a very obvious failure if it is bad.
 
Ok! I replaced the parts and now the machine lights up in the cabinet when the switch is thrown but does not let any smoke out! It also, however, does not start. I am thinking it makes more sense to start a new thread for this different issue, so I am going to consider this one closed.
Thanks very much everyone, this problem ended up being pretty pain-free!
-Parker
 








 
Back
Top