NX-700-K Toasty! Burnt circuit board...

[westcoaster]

Not sure if the power was hooked up backward or whether the radio was struck by lightning.
Either way it smells crispy in there.

Is this fixable? What components do I need?

Is it a multi layer board?

This is for an NX700-K

 

[kd4efm]

YUP, burnt.
Board replacement for sure or get a nx5700 OR NX-3720.
NX-700 EOL

 

[kd4efm]

 

[ramal121]

That's the protection diode. Power hooked up bass ackwards without a fuse? Clean it up, remove the diode and slight chance that a well placed jumper might restore power to the board. But by the looks of the moon crater I wouldn't hold out too much hope.

 

[mmckenna]

I can smell that photo.

 

[westcoaster]

I can smell that photo.

LOL

Yes, it has a distinct smell that anyone who has inadvertently let out the magic smoke knows all too well....

It was a gamble and I lost... Win some, lose some.... Although, it is providing some entertainment....

looks like L401, L402, and L403 vaporized (403 was barely hanging on and fell off with a touch of a screw driver....)

 

[westcoaster]

Well, the back side of the board survived....

What is L401, L402, L403?
D405 and C103? I can't read that last one.... Beside 401...

Thanks,

 

[mmckenna]

Reference Number Part Number Description
L402,403 L92-0179-05 CHIP FERRITE "Surge Absorption"
D405 DSA3A1 DIODE "Reverse Protection"
C103 CK73HB1E103K CHIP C 0.010UF K
I can't find a reference for L401, so maybe a space on the board, but not installed? CN401 is the B+ connector, is that what you are seeing?

 

[westcoaster]

No, It is L401 on the schematic above CN401 is off to the far right in IMG_6747
Looking at it, L401 may not have been installed. It may have simply been a couple pads on the circuit board.
At least nothing cratered underneath....

Looking at the way the traces have lifted, this is going to need some pretty creative redneck engineering if this thing ever wants to see life again....

 

[mmckenna]

If the control head is still good, save it and find an RF deck only sale on e-Bay.

 

[AM909]

Is F401 good (and hasn't been replaced)? If so, the damage may be confined to the crispy area. If it's blown, you'll have other bad stuff to deal with or, better, not.

 

[AM909]

The PA brick Vdd (IC102 pin 3) is also fed from unswitched B+ via ferrite chips L107, L108, and L109.

 

[westcoaster]

F401 does not appear damaged. Is it possible to replace the ferrite chips with jumper wire to see if the radio simply turns on?

The protection diode can be replaced with a jumper, just wondering about the chips...

Thanks,

 

[AM909]

Chip inductors can be replaced by jumpers for testing, yes.

You don't want to replace the D404 varistor or D405 diode with a jumper unless you want to see more flames.

 

[d119]

That must've been some hellacious current...

 

[n0fwg]

We had a bus fleet mechanic do the 24Volt jump start trick on several school bus's ONCE... That reverse protection diode is actually zener diode. Resulted in burned boards in the same area and PA audio amp etc.. His manager was not amused

 

[tlemke940]

Just to compare to a intact radio