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SX-780 Tuning

The soldering and modules looked original, the new ones didn't have the pins numbered like the ones I removed.
 
Three read 0.4

The one on pin 3 of the right channel reads 0.000

These are the big white square things ?
MPC70
0.22ΩK
FU78
 
Yes, sounds right, would need a picture to be absolutely sure, beyond say 98% sure.

0.4 on three and 0.000 is different than I expected, would you mind doing the ohmmeter test with one lead (pin 3 andf pin 8) of each resistor unsoldered and hanging in midair? DON'T turn the power on on while the resistors are disconnected.

I'm still looking for a suitable replacement, although that now I know it's a wire wound resistor, and they DIDN'T specify non-inductive, that makes it easier.


mouser.com 66-AS2R220J 0.22 ohms 2 watt $1.40 ea. no minimum order

digikey - struck out

partsexpress.com http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=015-.22 0.22ohm 5 watt $ 0.24 ea
no minimum order, $0.99 handling fee.
 
Since you are in DFW, you could try Tanner Electronics to find the 0.22ohm resistors (if needed). It would save you the shipping time. They are located on Valwood Pkwy just off 35E in Carrollton. Go to their webpage (www.tannerelectronics.com) for directions and phone number. If you visit their store (closed on Sunday), you will find them to be very friendly and helpful.

I just checked my drawer and I have some 0.22ohm (2W and 5W) that I know I bought at Tanner's.
 
Just had this SAME EXACT thing happen with my buddy's 780.

She's going now, singing like a bird, and I think it was an emitter resistor?? Whatever markthefixer said....:D

:lurk::lurk:
 
I keep reading these things and I must not know what's going on at all. I finally pulled all four out and checked.

3 are at 1.4Ω and the one on pin three of the right side is showing open, no continuity at all. Should I replace all four ? Maybe somethings up with this Fluke meter, I'll bring another one from the house tommorrow.


ji4m,
I had thought about going to Tanner. I think it would be just as well for me to order from Mouser, save gas and time getting from Forney to Carrollton. Mouser is just in Mansfield, so it should deliver pretty quick.
 
Mouser sells some Xicon 0.3 ohm vertical-mount 5W resistors (radial-lead, like the originals) that can do a nice job in the 780. # 280-PRM5-0.3-RC. I used them in the last 780 that needed emitter resistors.

Yes, I'd replace them all.
 
If you live close to **ehm** NTE dealers (eg. Fry's Electronics), they sell NTE 0.22ohm 5w. But they are axial leads. I used them along with my replacement module on one of my SX-780's channel that blew the output module cracked a couple resistors in process.
 
I brought in my meter from home. I'm getting 0.4Ω across the ones that still read.

Catch me up, I haven't messed with this since high school and these resisters are strange. Got the digital meter set to 200Ω, lowest it goes. The leads show 0.2Ω when touched together and the resistors show 0.4Ω when tested. Wouldn't that actually make them 0.2Ω after you subtract the resistance of the test leads ?
 
Beatnik said:
I brought in my meter from home. I'm getting 0.4Ω across the ones that still read.

Catch me up, I haven't messed with this since high school and these resisters are strange. Got the digital meter set to 200Ω, lowest it goes. The leads show 0.2Ω when touched together and the resistors show 0.4Ω when tested. Wouldn't that actually make them 0.2Ω after you subtract the resistance of the test leads ?
Click to expand...

Sounds good to me!! YES.....

BTW, I would go with EchoWars's recommendation, and I think I may get a few sets myself to have them around - at .36 each 10@.31 and 100@.23 it's a good idea.

I LOOKED straight at them recently on a 780 and it DIDN'T register they weren't axial - and I didn't pop the one on the shelf open and look yesterday before listing the stock numbers (I was too concerned with figuring out if they weren't "non-inductive").... shame on me......


(a while back I got frustrated with lo-ohm readings and the effects from the leads, so when I got the chance I jumped on a meter that does 4 wire resistance measurements, two carry the current and two are voltage probes and it has saved my a.. a few times now.)
 
Great ! I will order those today and should have them soon since Mouser is only across town.

Question, I could not tell if pin 7 on the module was actually soldered to the board or not ? It is now, is that right/okay ?

I took the camera and I hope this hack job passes. Pay no attention to where I marked for the resistors to go back in, that's so I don't do anything stupid when they show up. Took a picture of the resistors too.

pack2.jpg


resistors.jpg
 
Got the # 280-PRM5-0.3-RC resistors today. The leads on these things only extend about 3/16" below the bottom of the resistor and arealso only 3/16" apart. The holes on the circuit board are 3/8" between them. Do the axial ones have long leads like a normal resistor does ?

I haven't tried mounting them yet, but seems this might be a pain. I can use another empty hole on one leg that that is on the same tracer thing and will work better (you can see in the picture, the hole inside where I marked), but the resistor will be sitting right on the board and I won't be able to get a heat sink in there. Will these take the heat ?

EDIT: They are in there and the system seems to be fine now ! Not quite as punchy as my 6500II or the Nikko that she is borrowing, but that could be the crappy XM I'm using as a source. I'll add pictures tommorrow for the heck of it.

Pack1.jpg
 
Sorry, I should have looked closer at the pcb hole layouts, this is for future reference, and I have a dead one that I'm going to check against the 780 on the shelf:

It looks like a noble dual 0.22 ohm resistor will fit into some of those holes.

mcm electronics stocks them.

5 watts, rgc55-.22: @ $1.89 ea
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-RGC55--22-/28-0540

3 watts, rgc33-.22: @ $1.45 ea
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-RCG33--22-/28-0520

2 watts, rgc22-.22: @ $1.14 ea
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-RGC22--22-/28-0500

all three have 18mm 3 lead total spacing, 9mm between leads.
all are 5mm thick, 26mm wide and are either 9mm(2w), 13mm(3w) or 17mm(5w) tall (which isn't a problem, plenty of height clearance).
 
They're in there, be it a little tight, but looks good to me. :banana:

Thanks you so much for the help ! Hopefully my daughter will care for this for a long time to come.

sx-780resistors.jpg


sx-780powerpack.jpg


sx-780meters.jpg


sx-780face.jpg
 
Hey Beatnik, how about one more pic request of this 780 overhead shot with it's cover off, I never seen the innards of the 780, nice job! :thmbsp:







Thanks you so much for the help ! Hopefully my daughter will care for this for a long time to come.






sx-780face.jpg
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