Sx828 popping and crackling?

[PETER maas]

Hello. My sx828 is popping and crackling on the right channel. With volume down and pre amp leads in or out. Based on this I replaced the four Toshiba transistors on the heat sink. Found the replacement part numbers on another AK thread. But Still have that same popping etc. after this repair. Any other ideas? Thank you for your help!

 

[PETER maas]

Hello. My sx828 is popping and crackling on the right channel. With volume down and pre amp leads in or out. Based on this I replaced the four Toshiba transistors on the heat sink. Found the replacement part numbers on another AK thread. But Still have that same popping etc. after this repair. Every pot and switch has been cleaned/ deoxit. Any other ideas? Thank you for your help!

 

[markthefixer]

Surprised you didn't hear of "shoot on sight" transistors.

popping and crackling is rarely the output transistors, but rather the little transistors that control them.

 

[pa_200]

Had a similar problem on my SX-828. A few minutes after power on, crackling on the left channel, stayed on even with volume full down.

Removed top and bottom cover for some more checks and tests to isolate it to the main or pre amp. Big surprise, the crackling now was gone without touching any of the boards, the pre and main plugs are still in place.

The culprit transistors in question on the Main Amp AWH-010 have been replaced in 2020.
Will report back if I find out more.

 

[larryderouin]

Peter Maas; As Markthefixer alluded to, there are 'SHOOT ON SIGHT" transistors in the 828 that cause the issue's you're having. With your symptoms (preamp jumpers in or out), replace ALL of the 2SA726 (Q1 thru Q4) on the Amplifier board (AWH-010) 1st, then retest. Replacement is the KSA992FTA. ( https://www.mouser.com/ProductDetail/onsemi-Fairchild/KSA992FTA?qs=JV7lzlMm3yLxzxW6hzRppQ== ) Get 10 or so. They should be matched for hFe, as they are the differential pairs and determine offset to an extent. Do BOTH SIDES! (One time in, do it all).

Then go thru the whole unit and replace ALL 2sa725 and 2SA726 transistors on all boards that have them. If a position has a 2sa763 instead (it's an alternative to both the 725 and 726) leave them alone. The 763 has not documented a failure rate like the 725/726 pair.

2sc871 and or 2sc458's (problem children but not as extreme as the 725/726 pair) on the head amp (Phono board) all get replaced by KSC1845

pa200: did you replace the 725/726's in the AF unit and or the 2sc871/2sc458's in the head amp? Pull the preout/main in jumpers, volume to ZERO and fire it up for a 1/2 hour or until it crackles/pops. If it does crackle/pop with the preamp jumpers removed, the problem is in the amp. Any one source or all sources cause crackles????

 

[pa_200]

Hi Larry, it’s bewitched. With top and bottom cover removed, the unit plays perfect without and hiss or crackling. Maybe it’s the high temperature that we have since last week.
So I have to wait until the amp decides to start bothering me again.

 

[larryderouin]

Too long screws in bottom, top front, or sides for the cover???? If not, you have any canned air???? If you do,when it starts acting up start on the Amplifier boar and work back to the head amp. Short burst of canned air (flipped upside down so the liquid escapes) on each of the transistors. When it stops crackling/popping after a short burst on a transistor, wait for it to warm back up and let it crackle again. Then spritz it. That's your "BAD BOY" replace it and it's mirror on the other channel.

 

[JHS2RT]

My 828 did that---turned out to be bad points in the speaker relay.