420 Troubles

[michaellana]

I'm Having troubles with a drd420. When I plug the receiver in, resistor R14112 smokes. Any Idea on what could be causing this, besides the fact I'm plugging it in? I've downloaded the schematic but it doesn't help me trouble shoot it because I don't understand what I'm looking at. Any help would be greatly appreciated.

[skinerd]

Then why did you download schematic??????

You have a bad power supply, probably shorted diode in the low volt side caused an overload in the high volt side now you have trouble. Q14100 is shot and just changing it without repairing the low volt problems will just cause it to fail again. Don't plug it in again, or you may see sparks and fire when the resistors and Q14100 go up in smoke. This is not an uncommon problem with the 420 receivers.

[michaellana]

Thankyou for your reply skinerd. From what I read you are the best. I downloaded the schematic because I needed to know the value of burned resistors. I replaced resistors R14113(100 ohms), R14103(2.4k ohms), R14110(22 ohms), R14112(1k ohms) and C14105. I replaced these because they were burned black and I couldn't see what they were anymore.
I know it's probably alot to ask but is there a list of parts I could change to repair this problem? Obviously Q14100 will be on this list and I'll pick it up in the morning.

[michaellana]

Looks like CR14108 is on this list as well. Found that around 2 and 3 SS.

[skinerd]

Check all the diodes in the low voltage side, there are 4 CR14108 (-13v supply) is one. CR14104 (22v supply), CR14105 (5v supply), and CR14106 (3.3v supply) are the others.
If in doubt change it. CR14106 has a high failure reate also. These are special diodes, not just rectifiers, but either Schotty junction or very fast recovery.

[michaellana]

Thanks again Skinerd. I was able to pick up CR14104, CR14105 and CR14100 but CR14106 and Q14100 I was unable to find locally. Is there anywhere on the net I can go to find them?

[skinerd]

ST STP4NB50FP N-Channel Enhancement Power Mosfet, Q14100 is very important and few substitutes will work for it, I believer Mouser electronics has it.

For CR14106, NTE586 works fine.

[michaellana]

You are right again Skinerd. Mouser has a NTE replacement part for Q14100 (STP4NB50FP), CR14106 (NTE 586) and CR14102 (78-1N4148) and I didn't need a minimum order.

Just wanted to thank you in advance for your most valuable time and knowledge. The hobby needs more people like you. I'll drop a post and let you know how I make out.

[Armis]

It will probably be much easier to just replace the IRD with one from E-bay... By the time you get new parts, replace, and then MAYBE not smoke them again....

But if you're in it for the challenge, go for it! :)

Armis

[michaellana]

Once again Thanks Skinerd. I Soldered in my parts, plugged it in, and the unit works like the day it was purchased.

It was a great learning experience also.