trying to bring this back to life

  • Thread starter Thread starter dbas
  • Start date Start date
D

dbas

New member
Hi all, bought this Fostex XR-3 of ebay and like a muppet inserted a wrong power adapter and it started to smoke...as you do...:D
I think I found what burned so just wondering if I replace this resistor looking thing if it would power up, I couldn't see any further damage but could there be more than meets the eye? and can anyone identify the (d603) part?
I had a quick look on the internet but couldn't find it.
Thanks
 

Attachments

  • 2.webp
    2.webp
    58.4 KB · Views: 71
that would be a diode. It's the right size and the "D" in D603 means Diode.

Cannot tell the value. I'm guessing if it smoked, it might have protected the rest of the circuitry. Not that that it's job, but just because it was the first to die.
 
There's two ways to look at a blown component.
One is it's blown : If I replaced it it's fixed.
The other is it's blown : Something cause it to blow. If I replace it then new one will blow too!

Depending on your comfort and skill you might want to get a hold of a schematic and find out where that diode is in the circuit and what it's doing before replacing.
 
Chili said:
Not that that it's job, but just because it was the first to die.
Click to expand...
On the contrary, that really IS it's job. It is ostensibly a "reverse polarity protection" diode. Generally, these are not actually meant to protect the circuit, though. What they actually protect is the company from having to fulfill warranty claims when you use anything other than their approved power supply. It sort of protects the circuit by acting as a short circuit to stop the reversed power affecting other components, but only until it heats up and explodes. Once that happens, unless you get lucky and it destroys the traces that would get power to past it, everything else will just fry also.

Honestly, if it was only that diode that was damaged, you should be able to just remove it, use the correct power supply, and it should work. Like, it's not really necessary for normal operation. BUT I've never known that to be true. Every time I've ever seen this type of diode explode (usually in guitar pedals) the thing never worked again. You might not necessarily see anything that looks damaged, but it's pretty likely to have popped some of the other semiconductors in there somewhere.
 
I contacted a supplier earlier and the d603 is apparently the position on the circuit diagram and not the diode ID number as I originally thought. They require the voltage and the current rating in order to find a suitable alternative.

Btw I've also found the adapter I was "supposed" to use but I'll think I'll wait a bit see if I can get hold of the diode first before I use it as it's correct dc and voltage but not original.
 
Naw they don’t know what they’re talking about. It’s a power rectifier diode probably 1N4001 or similar. The voltage doesn’t much matter because it’s meant to be reverse biased anyway and any of that class of diodes will be fine with any sane DC wallwart . It’s not supposed to flow any current in normal use, and if it is conducting, the current will quickly approach infinity. Bigger would give you a better chance to avoid the explosion and actually protect your gear in future, but either way the V and A would be at most whatever the PSU is rated for.

The fun part about all of this is that there is an easy way to use that part to actually protect the circuit from both reverse polarity DC and AC (which is wrong polarity half the time) without exploding, but nobody ever builds their gear that way because again it’s about catching you using the wrong polarity supply and voiding your warranty claim.
 
Wow, they've caught me alright just about a couple dozen years too late. Thanks for the diode info man, needed that.
 
Do you have a schematic? And what PSU did you use vs what you were supposed to use? It seems more likely something else failed causing that diode to fail.
 
I had the correct psu in terms of power just used the wrong one, anyway I soldered the 1N4001 diode I got off ebay and it's working fine now (with the correct psu this time). Result, thanks guys.
 
Yep, I see a lot of pedal schematics that have power protection diodes. You are lucky it had that if you got it working again. Glad you got it fixed.
 
It's great that there are people who can give competent advice. I'm glad you made it. It's a good thing there are more units that can be repaired. Now, as a rule, everything is made disposable!
 
I have met these 'protection' diodes many times before Ash' but it never occurred to me that the b****s wire them wrongly to save their arses!

Logic would state you put the diode IN SERIES with the incoming supply. The slight, 0.6V loss is inconsequential for a mains derived supply but reverse polarity protection is afforded with no smoke!

OR, they could have fitted a 1R fusible wee resistor before the parallel diode which would save diode and downstream electronics.

Dave.
 
ecc83 said:
...they could have fitted a 1R fusible wee resistor before the parallel diode which would save diode and downstream electronics.
Click to expand...
There often IS a smallish resistor in series there, but then it’s kind of a race to death between the resistor and the diode. If the resistor explodes first, things downstream are safe, but if the diode pops first...

To be fair I’ve never heard a manufacturer actually admit that this is about warranty protection. Honestly I think most people do it because that’s how the circuit they “borrowed” from did it and they just never questioned. But yeah, even in 9V pedals, 0.6V drop isn’t much, and if you use a Shottkey (sp?) you lose even less.
 
You must log in or register to reply here.
Back
Top