Scratchy pot not coming clean
- Thread starter socrates75
- Start date
socrates75
Well-Known Member
i have done repairs on it myself but with help from people online telling me what to poke and prod at, with this unit i have replaced 3 transistors on the protection board, 4 by polar transistors on the power amp (one for each channel) and have adjusted the bias (that was a pain in the ass
) and cleaned all the pots and switches, i feel comfortable soldering, i just have a very bad memory so when ever i learn stuff i easily forget it 
if it sounds like to much work to help with then i 100% understand, believe me i would rather take it to a shop and have them figure it out but it would be costly and well just like most people, im broke lol as it stands the unit works amazing and sounds amazing, its just the start up process thats the problem, thats why im thinking its best to try the lubes first to rule out the easy stuff, then move onto the possibility of a capacitor problem (wich would make sense as these are all OG caps.....theres a lot :| )
You can check for DC on the pot sections easily. Connect the negative lead of the multimeter to the chassis, and set the meter for the lowest DC mode. probe each of the leads of the volume pot , and see if you see any DC voltage (there should be no more than a few milivolts, or none). You should turn the volume up some, so the wiper is not at the ground end of the element when checking. There will be 4 terminals for each section (low end, wiper, high end, and loudness tap)
Last edited:
socrates75
Well-Known Member
Ok thanks for the help man
i appreciate it 
i will be waiting till next week possibly to open this big ass guy i will let ya know what the results are 
2sa725,2sa726 transistors are notorious for getting noisy. I describe it as "Rice Krispies in Milk" Snap, Crackle, pop. And the 2sc1451 also. These 3 are on the AK "TOP TEN MOST WANTED LIST" Replace on site. The Amplifier board itself has 8 2sa726 and 4 2sc1451's. Do a pre-emptive strike and get rid of them before you REALLY have problems.
socrates75
Well-Known Member
I know i already replaced the 4 2sc1451 on the power amp board as i had read that those 4 could go out and take the whole system with them, so i know i put in new ones, but i hadn't heard about the other two, looking at the schematics ( its all a puzzle to me lol) i can only find the 2sa726 transistors, cant seem to find the 2sa725? what would i replace the 2sa726 with?
EDIT
Ok after looking around i see people suggest to replace the 2sa726 and 2sa725 with ksa992.
Found those on mouser.ca https://www.mouser.ca/Search/Refine?Keyword=ksa992
Just not sure which one i would pick from the list as there seems to be a lot :/
Last edited:
socrates75
Well-Known Member
Hey sorry man just didnt know if you had seen my last reply, would replacing the 2sa726 with ksa992 be right? and if so would these be the right ones? https://www.mouser.ca/Search/Refine?Keyword=ksa992 and does it matter which ones i pick from that list? as in are these just all the same ones but sold by different people?
socrates75
Well-Known Member
Can anyone help me with the right part to pick? https://www.mouser.ca/Search/Refine?Keyword=ksa992
also im going to be opening up the receiver in the next few days and testing the volume pot like AE BOB suggested, as im starting to think he might be right, when i turn the receiver on and the relay clicks i get the static sound from front left and back right when adjusting the volume, but if i turn the receiver on and let it sit for 2 minutes with out touching the volume and then turn the knob it doesn't make any noise except for a faint static from the back right.
also im going to be opening up the receiver in the next few days and testing the volume pot like AE BOB suggested, as im starting to think he might be right, when i turn the receiver on and the relay clicks i get the static sound from front left and back right when adjusting the volume, but if i turn the receiver on and let it sit for 2 minutes with out touching the volume and then turn the knob it doesn't make any noise except for a faint static from the back right.
socrates75
Well-Known Member
Ok i pulled the big bastard apart as i was getting sick of the popping and snapping noise right after start up,so with it open i placed the black prob on the metal chassis and turned the unit on, on my volume pot theres only 3 posts per speakers (4 speakers) so 12 posts in all, on the right side theres 4 posts with a black wire going to each and all 4 gave 00.8 then the middle posts,the first two posts gave 00.8 but the last 2 posts in the middle gave 02.7 then onto the last left side posts,the first one gave between 02.5 down to 00.7 and just jumped around by itself,second post gave 01.9 down to -00.6 and it to jumped around,3rd post gave a solid 01.3 and i think jumped down just a tad randomly,then the last one gave 01.8 and jumped around down as low as 00.3.
I hope i explained myself correctly, if not i can take a pic of my crude drawing of the posts
after i was done this i blasted the pot again with deoxit and rotated the knob about a 100 times,then flipped the unit upside down and rotated the know another 100 times, it moves freely but when turning slowly i swear it has an almost grinding effect....anyways im going to let it dry for about an hour and then plug it back in to see if the spray helped at all....if you can tell me what the results mean and how i move forward if they are not normal that would be amazing thanks again for the help EDIT
Ok turned it on and the scratching sound is completely gone, but this will probably only be for a week or so and then rear its ugly head
Last edited:
I am assuming the measurements you are showing are in volts, If that is true then you surely have some capacitors leaking DC on to the pot. I think the first thing I would do is replace C1 and C2 (1uf 25v) on both AWG-024 Control Amp PC boards. It sounds like there is some leakage through those capacitors back into the volume wiper, although it is hard for me to tell which elements of the pot you were describing in each measurement The center terminal is the wiper, and the black wire is the loudness tap (works with the loudness button). You can determine which of the two terminals is the high side of the pot by observing how the wiper goes from the low end (which is grounded) to the high side, as the volume is turned up. If you look at the foils on the PC board, all 4 of the low side terminals should be connected to one foil.That side will always measure very close to 0 volts as it is grounded. If you have leaky capacitors on the wiper, WITH THE VOLUME TURNED ALL THE WAY DOWN, the wipers would also measure very close to 0 volts as the wipers are effectively connected to the low side.with the volume all the way down. First look for any voltage on the high side of the pots (opposite the grounded side). If any is there the issue is likely in a previous stage(before the volume control). If there is no voltage on the high sides then turn the volume up some (25-50%) and measure the wipers again. If there is now voltage on the wipers then the downstream C1 and C2 on the control amp boards are likely leaky.
socrates75
Well-Known Member
Well from what you describe, it sounds exactly like what your saying,when i was reading the high post it would go up as i turn the volume up which would indicate as you said to be the caps on the tone control boards,it would be the cheapest and probably the easiest parts to replace on any of the boards as i can pull them out and have lots of room to work with on them,unlike the other boards in side lol its going to be about a month before i can order the replacement caps and open back up, so i will let you know once i have them ordered, would you happen to have a link to these caps? and well im on those boards should i replace the transistors on them as well? and if so with what?
What about buying this kit?
https://www.ebay.ca/itm/Pioneer-QX-...650866?hash=item1cf0991e32:g:3jgAAOSwtrdfM9Ac
Last edited:
I am not one to just start replacing parts without a good reason. I would certianly replace all the 1uf 25v caps on the board, and would measure the voltages on the others with a multimeter, and see if any others are showing signs of leakage (voltage on the lead that should not have any). Those 1uf electrolytic capacitors could be replaced with film capacitors if you like.
socrates75
Well-Known Member
Ya i also just realizes the price on those parts with shipping would be close to 50 bucks, so maybe just replacing the caps you mentioned would be a good idea
thanks man i will update this thread when i have ordered and received the parts
socrates75
Well-Known Member
Hey man im about to order the caps you suggested to replace and wanted to know if you could take a look at what i have picked as the replacement and tell me if its ok?
https://www.digikey.com/en/products/detail/nichicon/UFG1H010MDM1TD/4317871
im only replacing the 4 of them but i will probably order 8 just in case i **** up
socrates75
Well-Known Member
ordered the parts.
socrates75
Well-Known Member
Ok got the caps, going to replace them today as well as the transistors on the front speakers control board
socrates75
Well-Known Member
oops double post
Last edited:
socrates75
Well-Known Member
oops double post
socrates75
Well-Known Member
Ok installed the new 1uf 50v caps and the rest of the transistors and its still making the popping snapping sound when first turned on and then fades, only thing i can think it could be is my bad soldering job on the power amp board where i replaced a few transistors months ago and lifted a pad by accident,so i had to drag some solder from one leg of the transistor to a spot that i cleaned.....it just so happens this **** up is on the 4th channel, the one causing the pops....can i not bridge it with solder like that or should i have used a wire to bridge it? and can this bridge i made of solder cause these popping problems when first turned on?