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Pioneer SX-1250

DMM - Digital Multi Meter, with "diode test".

Plenty of posts on what to get for them....
 
got a quick update for you, mark or whoever wants to give any info. i got the 1250 hooked up as a power amp and it plays on both side, but the left channel pops and cracks every now and then, will update again if right channel pops or cracks. Do you think the flat amp board and the control amp board is the cause of the problem?

Edit: Right channel played for an hour straight with no pops or cracks. I noticed the left heatsink get a lil warm and the right
side stays cool

Edit#2: I Just played left channel for an hour with 2 faint scratching noises, only noticed it cause music wasn't playing very loud, and there was no popping out of the left channel at all, left heatsink stays around same temp no matter if it's playing thru it or not.
 
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To isolate the pop etc stuff to the power amp, just let it sit without the power amp input connected (pull the jumpers) and listen for pops etc...

IF the pop is from both channels at the same time, then we look at the power supply.
 
it only pops and cracks from the left channel, pre-amp is still messed up though, getting ready to get a dmm and test the mv's out of both sides of the speaker outputs, will update once i have tested them. thanks for your help, mark
 
i got a dmm at advance auto, hooked it up to V,ohm, ma and com and set to 200m, and the reading fluctuates real bad on right channel -40.5 to -70.0, i tested the left channel and it's showing -4.5 to -6.5 after about 10 minutes of testing, right channel seemed to have nothing wrong with it when playing music through it, left channel pops and cracks
 
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if anyone else out there can help me out with this, you're welcome to post. i am a noob at repairing electronics, but i am a fast learner. any help is greatly appreciated
 
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Pull the jumpers out of the back of the receiver and check the speaker terminals again. Also, always Do your voltage adjustments in AUX. I believe Deoxit will fix some of your problems.
 
markthefixer said:
To isolate the pop etc stuff to the power amp, just let it sit without the power amp input connected (pull the jumpers) and listen for pops etc...

IF the pop is from both channels at the same time, then we look at the power supply.
Click to expand...

xXColdShotXx said:
i got a dmm at advance auto, hooked it up to V,ohm, ma and com and set to 200m, and the reading fluctuates real bad on right channel -40.5 to -70.0, i tested the left channel and it's showing -4.5 to -6.5 after about 10 minutes of testing, right channel seemed to have nothing wrong with it when playing music through it, left channel pops and cracks
Click to expand...

xXColdShotXx said:
if anyone else out there can help me out with this, you're welcome to post. i am a noob at repairing electronics, but i am a fast learner. any help is greatly appreciated
Click to expand...

paul79 said:
Pull the jumpers out of the back of the receiver and check the speaker terminals again. Also, always Do your voltage adjustments in AUX. I believe Deoxit will fix some of your problems.
Click to expand...

My advice still stands, and I am waiting for you to follow it, please advise exactly what pins you were measuring - I'm not sure if you are talking about idle current or offset voltage.

my advice will vary GREATLY depending upon which pins / specification you are actually measuring.

pull the jumpers, make the measurements and shut it back down, there could be serious troubles lurking in some intermittent potentiometers in the amp - smoke level serious.
 
I read some of EW's thread, amplifier distortion, dc-offset, and you. I tested the speaker terminals of A selection, both sides and got the readings of right channel -40.5 to -70.0 and the left channel and it's showing -4.5 to -6.5. i had the pre-amp/power amp jumpers in and it was set to tape monitor 1 i beleive.
 
just tested speaker terminals right and left of A selection with pre-amp/power amp jumpers out and Aux selected, readings were right channel -21.5 to -28.0, left channel -5.1 to -7.0, neither of them were steady, always fluctuating.
 
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i am assuming mv's, got the dmm set to the side with the big V and dial is on 200m, that's only way it brings numbers up on the display

Edit: here's a pic of my dmm, i know it's cheap, but can't afford a fluke just yet.
5760112_dor_85357_pri_larg2.jpg
 
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Looks like mine except mine is black. It works just fine for biasing and some other measurement. The downside is it seems to draw 10x current compared to my B&K doing measurement.
 
If you meant the setting on the meter to 200mv, then yes. If you are referring to posts # 32 and 33, then either it's misunderstood as volts or you are getting that much. Just an advice, if you find the reading in millivolts then when you post them here, make sure you use "mv" at the end of the numbers. ex: 100mv, -21mv, etc. If you're getting actual volt reading (not millivolts) then just use "v". ex: 65v, -65v, etc. So we can differentiate what your findings are.
 
I assume you are talking about the DC offset right? If so, you want to try bringing it to or close to 0.0mv. Small fluctuation like a few millivolts is ok but any larger should be checked out. And the

If your heatsink gets pretty warm in a few minutes, you better check your bias. Bias should be 100mv. That too will fluctuate a few millivolt if working properly. If it exceeds 100mv and if you turn the pot and it fluctuates wildly, then shut it off immediately. I experience that problem a few years ago on my 1250. Left channel was getting torching hot while the right was still cool within just 5 minutes. Cause? Bad trimmer pot and my bias was way over 300mv.
 
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