Pioneer SX-636 left ch. low

dukeofurl

Active Member
While having my morning coffee my receiver made an loud-ish pop (from the speakers) so I quickly switch it off. (The receiver was on most of the night with the radio in the background, so this didn't happen while turning on the power).
Came back to see what's going on after returning home from work and I find that my left channel is very low but not distorted.
Pulled the covers off and located the signal path, to the power amp, to check if the power amp stage was ok. - Yes, I can inject a signal with both channels working. :)
So, this leads me to think that the preamp is at fault. (same low level, left channel, with all inputs and radio).

Can some good soul help me to track down the problem?

Thanks in advanced!!
 
Good trouble shooting so far.

A good Deoxit cleaning?

Shot Gun:
As Larry would say "Get those 2SA726's out of the AF amplifier Assembly". The small Mylars get replaced with Stacked film.

Q1 is the left chanel and Q2 is the right. You could swap them (Or just replace them with KAS992's). Or set the DMM to ACmV with an input (Like a CD playing) and see if you are getting anything out of collector side of the left channel 2SA726. Compare it to the right. Then completely rebuild the board which will cost more in shipping than the combined parts from Mouser.

This is where the the systematic trouble shooting ends. :D
 
Last edited:
Is this condition in ONE MODE (for example, FM only) or ALL MODE's? Mono or Stereo, or Both?

The 636 has a troublesome pair of transistors. 2sa726 and 2sc1451.
These are the most troublesome transistors in the x2x thru some x50 series of receivers. They get noisy, and cause all kinds of problems. Whether or not one or the other caused your current problem, they are to be pre-emptively replaced or they WILL go bad and cause lot's of problems. It's a When they go, not an If they go.
The close sibling of the 2sa726 is the 2sa725. Same problem.

Replacement transistors. Fairchild manufactured. Available @ mouser

2sa725 or 2sa726 ----> KSA992FBU
These are on the AF ASSY BOARD (AWK-035)

Also possibly on the Q1-Q4 positions on the Amplifier board (AWH-034)
It's listed as an alternate to the 2SA763.

The 2sc1451-----> KSC3503DSTU
Amplifier board AWH-034.

In the EQ Board the 2sc1312 can be replaced with the KSC1845

See this post from 2011 reference to a 636 with Snap, crackle, pop. http://www.audiokarma.org/forums/showpost.php?p=4708066&postcount=4
in this thread http://www.audiokarma.org/forums/showthread.php?t=373254&highlight=sx636

If the 636 has never been worked on it would be a good idea to recap it while you are in there. The caps are way past their use by date. 20 years is the recommended replacement age. These are pushing 40.

I'll see if I can find the Recap list thread. You'd need to copy the list, repost it in this thread and have it vetted for out of date or obsolete parts.

CLEAN THE UNIT 1st. Dust it out, and DeOxit ALL of the switches and pots.

Read this thread in the General Forum ("The idiot's guide to De-Oxit.....Revisited") To paraphrase Mark the Fixer; If it goes in/out, up/down, or Round and Round, it gets DeOxit. Back it up with FADERLUBE as DeOxit washes out most if not all the lubricant.

The problem could be a combination of a transistor and caps, or either one.
With the unit running compare voltages starting at the amp and work back to the inputs. Compare the good side with the bad side.

Start with the 2sa726 and 2sc1451's. Then if it doesn't correct it, we go a little further.
 
yup, sounds like preamp. (transistors probably, or the sanyo caps)

definitely get RID of all the 2sc1451's in the power amp, they are ticking time bombs to your output amplifiers, sort of like a self destruct - the other transistors will cause quiet, but these will cause DAMAGE.

Also get ALL sky blue Sanyo Cap - capsistors out of the unit.

These are non negotiable. built in trouble. Solid history of slowly shorting out, and acting like resistors. Not IF, but rather, WHEN.

The rest of the recommended changes with deoxiting and regreasing will end up giving you a receiver that will be covered in dust many years from now before you need to go back in and fix something else.
 
Last edited:
Thanks so very much to you all!!
Yes, all input selections have the same results. (AM, FM, TAPE,.. etc.)
I've located the schematic and will begin the long and winding task tomorrow. :)
 
Is this condition in ONE MODE (for example, FM only) or ALL MODE's? Mono or Stereo, or Both?

All modes, also both in mono and stereo.

Yes, PLEASE, if you happen to have a shopping list that would be so helpful, I plan to deal with the preamp (caps and transistors) all at once then when all is well, head straight for the power amp transistors.

I don't mind ordering the entire lot of components at the same time if the list permits. :)

Thanks so very much again!
 
This is the SX-636 recap and transistor list found on the data base.
No telling the date so look it over carefully.

Pioneer SX-636 recap:

Equalizer Amp Assembly (AWF-014-0)

AWF-014-0: C1: 3.3uF 10v CSZA: 647-UKL1H3R3KDDANA 3.3uF 50v
AWF-014-0: C2: 3.3uF 10v CSZA: 647-UKL1H3R3KDDANA 3.3uF 50v
AWF-014-0: C3: .47uF 50v CEA: 667-ECQ-V1H474JL .47uF 50v
AWF-014-0: C4: .47uF 50v CEA: 667-ECQ-V1H474JL .47uF 50v
AWF-014-0: C5: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v
AWF-014-0: C6: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v
AWF-014-0: C11: 22uF 10v CEA: 647-UPW1C220MDD6 22uF 16v
AWF-014-0: C12: 22uF 10v CEA: 647-UPW1C220MDD6 22uF 16v
AWF-014-0: C13: .47uF 35v CSZA: 667-ECQ-V1H474JL .47uF 50v
AWF-014-0: C14: .47uF 35v CSZA: 667-ECQ-V1H474JL .47uF 50v

AWF-014-0: Q1: 2SC1344 2SC1312; 512-KSC1845FTA
AWF-014-0: Q2: 2SC1344 2SC1312; 512-KSC1845FTA
AWF-014-0: Q3: 2SC1344 2SC1312; 512-KSC1845FTA
AWF-014-0: Q4: 2SC1344 2SC1312; 512-KSC1845FTA

AF Amp Assembly (AWK-035-0)

AWK-035-0: C5: 1uF 25v CSZA: 667-ECQ-V1H105JL5 1uF 50v
AWK-035-0: C6: 1uF 25v CSZA: 667-ECQ-V1H105JL5 1uF 50v
AWK-035-0: C9: 100uF 16v CEA: 647-UPW1E101MED 100uF 25v
AWK-035-0: C10: 100uF 16v CEA: 647-UPW1E101MED 100uF 25v
AWK-035-0: C13: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C14: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C21: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C22: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C23: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C24: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWK-035-0: C25: 2.2uF 25v CSSA: 647-UKL1H2R2KDDANA 2.2uF 50v
AWK-035-0: C26: 2.2uF 25v CSSA: 647-UKL1H2R2KDDANA 2.2uF 50v
AWK-035-0: C27: 47uF 10v CEA: 647-UPW1C470MDD 47uF 16v
AWK-035-0: C28: 47uF 10v CEA: 647-UPW1C470MDD 47uF 16v
AWK-035-0: C31: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v

Q1: 2SA726: 512-KSA992FBU
Q2: 2SA726: 512-KSA992FBU

Power Amp Assembly (AWH-034-0)

AWH-034-0: C1: .33uF 25v CSSA: 667-ECQ-V1H334JL .33uF 50v
AWH-034-0: C2: .33uF 25v CSSA: 667-ECQ-V1H334JL .33uF 50v
AWH-034-0: C7: 220uF 6.8v CEA: 647-UPW1A221MED 220uF 10v
AWH-034-0: C8: 220uF 6.8v CEA: 647-UPW1A221MED 220uF 10v
AWH-034-0: C9: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
AWH-034-0: C10: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v

Q1: 2SA726: 512-KSA992FBU
Q2: 2SA726: 512-KSA992FBU
Q3: 2SA726: 512-KSA992FBU
Q4: 2SA726: 512-KSA992FBU
Q5: 2SC1451: 512-KSC3503DS
Q6: 2SC1451: 512-KSC3503DS

Power Supply Assembly (AWR-060-0)

AWR-060-0: C6: 470uF 50v CEA: 647-UPW1H471MHD 470uF 50v
AWR-060-0: C7: 220uF 50v CEA: 647-UPW1H221MPD 220uF 50v
AWR-060-0: C8: 220uF 50v CEA: 647-UPW1H221MPD 220uF 50v
AWR-060-0: C9: 100uF 50v CEA: 647-UPW1H101MPD 100uF 50v
AWR-060-0: C11: 100uF 16v CEA: 647-UPW1E101MED 100uF 25v
AWR-060-0: C12: 220uF 16v CEA: 647-UPW1E221MPD 220uF 25v
AWR-060-0: C13: 10uF 35v CEA: 647-UPW1V100MDD 10uF 35v
AWR-060-0: C14: 220uF 50v CEA: 647-UPW1H221MPD 220uF 50v
AWR-060-0: C16: 100uF 16v CEA: 647-UPW1E101MED 100uF 25v

BOM List

647-UKL1H3R3KDDANA | 2
667-ECQ-V1H334JL | 2
667-ECQ-V1H474JL | 4
647-UPW1E101MED | 4
647-UPW1C470MDD | 2
647-UKL1H2R2KDDANA | 2
647-UPW1V101MPD | 3
647-UPW1V470MED | 2
647-UPW1H221MPD | 3
667-ECQ-V1H105JL5 | 2
647-UPW1V4R7MDD | 6
647-UPW1H101MPD | 1
647-UPW1C220MDD6 | 2
647-UPW1A221MED | 2
647-UPW1E221MPD | 1
647-UPW1H471MHD | 1
647-UPW1V100MDD | 1
512-KSC1845FTA | 10
512-KSA992FBU | 20
512-KSC3503DS | 10
 
So far I have my shopping list down to the last component on the power amp section:

Q5: 2SC1451: 512-KSC3503DS
Q6: 2SC1451: 512-KSC3503DS

..... got stuck on these at Mouser.. any idea on that one please?

oh, .. what is "BOM" list?
 
Last edited:
The BOM is a convoluted way to order the entire list in a spread sheet form. I use it, but in most cases I just order the BOM one line at a time (The second number is the quantity). If I were more organized I would use it.

What do you mean Q5: 2SC1451: 512-KSC3503DS, Q6: 2SC1451: 512-KSC3503DS. Order them up. 512-KSC3503DS or 512-KSC3503DSTU

Wait and make sure MTF or Larry vet the list. I think every thing is up to date but they may have a additional component to add.
 
Last edited:
The DS or DSTU suffix is the gain letter and the method packaging they use.
DS is gain and lead length. Blank after DS is BULK (lot of loose in a bag)
DSTU is TUBE (lots of them lined up in a tube, then stuffed in the bag).

I guess it depends on how OCD you are as to which packaging you get. SAME PRICE!

The Data sheet backs it up.

*1. Affix “-S-” means the standard TO126 Package.(see package dimensions). If the affix is ”-STS-” instead of “-S-”, that mean the short-lead TO126 package.
2. Suffix “-TU” means the tube packing, The Suffix “TU” could be replaced to other suffix character as packing method.

They are fine, go ahead and get which ever one tickles yer fancy.
 
The BOM is a convoluted way to order the entire list in a spread sheet form. I use it, but in most cases I just order the BOM one line at a time (The second number is the quantity). If I were more organized I would use it.

What do you mean Q5: 2SC1451: 512-KSC3503DS, Q6: 2SC1451: 512-KSC3503DS. Order them up. 512-KSC3503DS or 512-KSC3503DSTU

Wait and make sure MTF or Larry vet the list. I think every thing is up to date but they may have a additional component to add.

Ah,.. yeah, Larry kind of answered the 512-KSC3503DSTU thing... I wasn't sure of what to pick at Mouser since it came in 2 varieties.

As for the BOM thing... now, that totally messes with my fragile mind... hehe.. I still don't get that bit at all. (sorry for my stupidity) ... those BOM order numbers with the amounts to purchase, is that in addition to the list above those?

Thanks again to you both for your guidance. :)
Really looking forward to getting this receiver back to good health.
 
The BOM List

Yes; just a consolidated list with the quantitys after the part number. You can use the Mouser BOM tool to drop a spread sheet in but you only need to order a little more than a hand full of parts. Just copy the part number into the mouser part number block and add the quantity manually for each of the components. 10 minutes at best. Check and make sure that the mouser quantity's are there before you move to the next part number. You may have to choose the next equivalent which in most cases will be a newer lot (Batch).

When you move on to the 1250 or 1980 (And it will happen!) we can add more info on how to use the BOM. :D
 
Last edited:
Actually the BOM is quite easy to use. It's a consolidation of all the part #'s with quantities collated. Then you copy it and paste it in a BOM box, it enter and your order is loaded. Verify it, and purchase.

Mark has it down to a science with almost every model receiver listed, and will check an old list, make corrections, and re-issue it with updated part numbers and quantities.

The upper 1/2 of the list is mainly for you to check each component against your boards. There are changes on these that does not get documented in the Service manual. So if/when you come across a part that is different note the new value/voltage/ transistor #, etc. and post it up here. That info will be researched for the new part, and the corrections will be made and you end up with the latest and greatest list for your model that is specific to your particular serial #.

When the updated list is reposted then you get the OK to order. Make a copy of the whole list and keep it with your service manual. When the parts come in you can break down the order by board, and then start the re-construction.

It sounds complicated, and daunting for a 1st timer, but it's not that hard. And it gets easier everytime you do it.
 
Ah, yes, now I understand the BOM idea.
I did copy and paste into the BOM box but stumped after that. (Love the idea though!)
I'll just manually sort out the order since there's not alot to purchase.
Would it be a good idea to replace the 2 larger power supply caps while I'm at it?
 
Would it be a good idea to replace the 2 larger power supply caps while I'm at it? If so, do we have any order numbers for those?

Once again, thanks for all of this wonderful information!
 
I usually hold off on the POWER FILTER CAPS, unless there is an overiding reason to do so, ......Leaking from the caps, power supply hum, etc. But I DO replace them shortly afterwards. They are the largest caps there, have the most electrolyte and unless they have vented or are humming, still are carrying most of the electrolytic.

The replacements for these are quite a bit smaller than the originals, and there are many to choose from. You can go higher in value and voltage a bit. for a 6800uf/35v cap you can go 8000uf/50v without hurting the unit with inrush current.

If they aren't leaking, or causing a power supply hum, I'd leave them for now, and research them separately.

Larry
 
Right, I finally got around to separating all of the caps for the various jobs. (starting with the preamp section).
Regarding transistors.. I have 20. (2 to be installed).
Can anyone point me onto the directions of matching these please?
 
Does your DMM have a setting called hFe? If not go to a local Harbor freight and get one of their cheapy DMM's. I think they run about $7.99 and can be had on sale for less than $4. SA and SB transistors are PNP, SC and SD are NPN. Looking from left to right with the flat facing you and the legs DOWN, on the KSA992 and the ksc1845 the legs are ECB. Stick the transistor in the meter, with the legs matching the holes, and wait a minute or two for it to stabilize. Just your body heat from your fingers will mess with the hFe (gain). write down the reading on a big sheet of paper and put THAT transistor next to it. Go on to the next. Try to get 2 that have the same gain, or as close as possible. being 5 off won't affect balance, but a difference of 100 WILL. The 992's that I've tested have all been within 20 low to high with the majority somewhere in the middle.
 
Thanks Larry, helped a lot! - Managed to get a couple matches for those transistors.

Was just preparing to get a start on the preamp section but was wondering:
AF Amp Assembly (AWK-035-0)
AWK-035-0: C5: 1uF 25v CSZA: 667-ECQ-V1H105JL5 1uF 50v
AWK-035-0: C6: 1uF 25v CSZA: 667-ECQ-V1H105JL5 1uF 50v

The original C5 & C6 look to be tantalum. - The new ones (CSZA: 667-ECQ-V1H105JL5 1uF 50v) look quite different with no positive or negative sides. - Does this sound correct?
 
Back
Top Bottom