SX-838 troubleshooting assistance please

[Uncle Bambi]

John:

Yep. Use the separate preamp, and connect it to the MAIN IN jacks. This takes and makes the 838 an amp only. Everything else is disconnected from the amp. All your sources would be connected to the separate preamp. If the noise continues in this variation, then the problem is in the amp.

OK - did this. I connected the MAIN OUT on the pre-amp to the POWER IN of the receiver.

I did not get any radio signal through the speaker (no tuner or other input device connected), but I did get light "white noise". After about the same amount of time as before, I heard crackling, popping, then silence when the 838 switched off.

Amplifier issue, no?

I'm trying to scrounge an amplifier to perform the reverse test, but I'm thinking it might not be necessary?

Just for fun, I measured a couple of pins on the protection circuit - red lead on pin, black on chassis ground. did I mis-read the schematic or not measure pin 12 properly, or is this a big, fat clue?:

On the Protection Circuit PCB:

Pin 01 +36.2-----s/b +35
Pin 12 8Vac-----s/b 75Vac

 

[PacificStereo]

Ah, yes, the TO-1 in-a-heatsink timebomb-in-a-can 2SC1451. We stocked this part by the billions for good reason.

Uncle B, what store did you get that 780 from?

 

[Uncle Bambi]

AUncle B, what store did you get that 780 from?

San Fernando Valley - Canoga Park, maybe?

Hopefully, it doesn't use the "timebombs".

 

[larryderouin]

OK - did this. I connected the MAIN OUT on the pre-amp to the POWER IN of the receiver.

I did not get any radio signal through the speaker (no tuner or other input device connected), but I did get light "white noise". After about the same amount of time as before, I heard crackling, popping, then silence when the 838 switched off.

Amplifier issue, no?

Yes it's an amp problem. Now i'll turn it over to MARK!

I'm trying to scrounge an amplifier to perform the reverse test, but I'm thinking it might not be necessary?

probably not, but why guess.

Just for fun, I measured a couple of pins on the protection circuit - red lead on pin, black on chassis ground. did I mis-read the schematic or not measure pin 12 properly, or is this a big, fat clue?:

On the Protection Circuit PCB:

Pin 01 +36.2-----s/b +35
Pin 12 8Vac-----s/b 75Vac

Your's are ok so far.

Look at the schematic again, and follow the pin 12 line all the way back to the power supply, It's supposed to be 7.5 (SEVEN POINT FIVE) volts AC.

What is your line voltage at the wall. Remember all the readings that are on the schematic are based on an IDEAL WALL VOLTAGE OF 117VAC. If your wall voltage is in the low/mid 120's all your voltages will be proportionatly higher.

If you're not sure of voltage on the schematic, blow up that section on the screen until it's clear. Sometimes a decimal is hard to see, especially with all the artifacts that copying puts into it. That's why I buy 99% of all my copys from Rick Stout @ Stereomanuals.com. they are a little higher in price than most, but his reproductions are as good as or better than the originals.

Larry
Back to you, MARK for the Heavy Duty Stuff.

 

[Uncle Bambi]

Yes it's an amp problem. Now i'll turn it over to MARK!



probably not, but why guess.


Your's are ok so far.

Look at the schematic again, and follow the pin 12 line all the way back to the power supply, It's supposed to be 7.5 (SEVEN POINT FIVE) volts AC.

What is your line voltage at the wall.

Funny you should ask - 118Vac. It was the first thing I checked, even before starting the thread. Should have mentioned it.......

Maybe I'm stupid....... but I've been searching the forum for a long time now, trying to get a parts list together. I've tried all kinds of search strings, and have yet to hit on anything relevant.

 

[markthefixer]

Funny you should ask - 118Vac. It was the first thing I checked, even before starting the thread. Should have mentioned it.......

Maybe I'm stupid....... but I've been searching the forum for a long time now, trying to get a parts list together. I've tried all kinds of search strings, and have yet to hit on anything relevant.

what?/ what I did above, yesterday afternoon, doesn't count??? I didn't have time to cross the caps yet nor add the transistors and then cross them.

maybe mattsd can take the list and do for you what he did for stevecivic's sx-3800 thread:http://www.audiokarma.org/forums/showpost.php?p=4315622&postcount=25
by add the transistors I mean look up each qx transistor number and dx diode number and post them after the capacitors in the list:
aaa-000 q1 2sa725
aaa-000 q2 2sc1451

and so forth for the different boards.

for the next five weeks I am going to be busier than the Devil in Las Vegas.... so my time on the forums will be severely reduced. If I catch up, Then I will be on the forums a bit more often....

BUT I stole too much time from this outside issue to instead post on this forum, and now it's coming back to bite me on the a** with a vengeance. It's a deadline I have no control over, and a longstanding commitment I cannot shortchange.

 

[Uncle Bambi]

what?/ what I did above, yesterday afternoon, doesn't count??? I didn't have time to cross the caps yet nor add the transistors and then cross them....

Oh, no.... you misunderstand..... it helped a great deal! I'm just a bit frustrated with my inability to search the forum properly so I can help myself. I want top be able to do the cross-matching and fill in the blanks - I just haven't been able to dope it out on my own.

I appreciate your time, patience, and expertise, and good luck catching up on your projects.

 

[Uncle Bambi]

phono amp
awf-011 c1 1 25 cssa 1 50 667-ECQ-V1H105JL5
awf-011 c2 1 25 cssa 1 50 667-ECQ-V1H105JL5
awf-011 c7 330 6 cea 330 10 647-UPW1A331MPD
awf-011 c8 330 6 cea 330 10 647-UPW1A331MPD
awf-011 c11 3.3 25 ceanl 3.3 50 647-UKL1H3R3KDDANA
awf-011 c12 3.3 25 ceanl 3.3 50 647-UKL1H3R3KDDANA
awf-011 c17 100 25 cea 100 25 647-UPW1V101MPD
awf-011 c18 220 16 cea 100 25 647-UPW1E221MPD

Ok - I'm getting around the mouser site pretty well now, and am getting the hang of crossing for parts. In the snippet above, I notice that you are replacing original caps with replacement caps of a higher voltage value. And on the last one, the uf values don't match.

Am I reading it wrong, or is there yet something else I'm failing to grasp?

 

[mattsd]

Higher voltage caps do not hurt anything, you cannot always find the cap in the same voltage as the original, so it is standard to go to the next higher voltage. As long as the capacitance remains the same, and the voltage within a reasonable level, you're fine.

As for this:

awf-011 c18 220 16 cea 100 25 647-UPW1E221MPD

that is just a typo, notice the 221 in the cap number, that means 220uF. 101 would mean 100uF, 100 is 10uF, 331 is 330uF and so on. Here, read this, it will give you some insight into what the caps are about: http://www.audiokarma.org/forums/showpost.php?p=3012505&postcount=11

Mark, if you need my help, I'm ready and waiting!

 

[Uncle Bambi]

Higher voltage caps do not hurt anything, you cannot always find the cap in the same voltage as the original, so it is standard to go to the next higher voltage. As long as the capacitance remains the same, and the voltage within a reasonable level, you're fine.

As for this: that is just a typo, notice the 221 in the cap number, that means 220uF. 101 would mean 100uF, 100 is 10uF, 331 is 330uF and so on. Here, read this, it will give you some insight into what the caps are about: http://www.audiokarma.org/forums/showpost.php?p=3012505&postcount=11

Mark, if you need my help, I'm ready and waiting!

Ahhh... so. Thanks for the reference link on caps - I'll study it closely.

Now, let's test my cross-referencing ability....for example, the three big caps on the sub chassis:

Example 1:
C1 8,000uf 50v ACH-015-0 REPLACE WITH 598-DCM802U50BA2B

They are the same value, and the same size. The only difference that I can see is that the original is leaded with wire-wrapped connections, and the replacement is screw terminal.

Example 2:
C3 1,000uf 63v ACH-001-C

This one is a problem child. The original is leaded, and has dimensions of 30mm diameter x 45mm high. I can't find a replacement that is the same size and value. The closest I can find is:

647-UPM1J102MHD1AA

Which is the same value, but about half the diameter.

Then there's this one:

598-DCM102T100AK2B

It is 1000uf, but 100v. And the diameter is about 5mm larger than the original, so it won't fit into the mount.

 

[mattsd]

Ah yes, that pain in the butt problem of trying to find caps that fit. Well, there are several ways of getting around that, if you do a search you find a lot of suggestions. Two ways I've seen is use weather-stripping to sort of line the clamp and take up the excess space. Or, you can use what Mark does, I quote:

I have mounted ( in the formerly clamped caps places) caps soldered into a small oblong pcb that had holes that matched holes in the chassis, and most of the foil removed to avoid shorts.

Find a way that works best for you and that holds the cap snugly, so it doesn't slip out.

Edit: Oh, and for cross-matching the caps, here is a rule of thumb:

cea radial general purpose: replaced by Nichicon UPW, UHE or Panasonic FM and FC in that order.
ceb axial general purpose: Nichicon TVX.
ceanl low leakage electrolytic (lower noise): Nichicon UKL.
cssa: Nichicon UKL.
csza: Nichicon UKL.
Use Nichicon UES, UEP & UVP in that order for bipolar depending on what is in stock.
If any of the above is between 0.1uF to 2 uF I use stacked film where they fit: Cornell Dubilier DFS and Panasonic ECQ, otherwise the
Solid aluminum and tantalum caps get stacked film when possible, or Nichicon UKL’s otherwise.


c?b means it's an axial cap = one lead on each end
c?a = radial = both leads on one end

 

[Uncle Bambi]

More excellent information, thanks!

OK - I want to step back for a sec.... The receiver is faulty, and apparently has an issue in the amplifier. Given - I need to re-cap, and given - I need to replace those problem transistors that Mark specified.....

Before I order a whole bunch of parts and shotgun the receiver, should I not try to isolate the fault first, and get the unit working?

If so, I could use some further assistance with that.

 

[markthefixer]

We HAVE isolated it as closely as possible for this situation, the fault IS the transistors I recommended, the 1451's with a smaller probability of the 2sa726's also being faulty.

You want to try to catch the exact one of the three in the act, or just replace them with under 2 bucks worth of transistors and have the problem go away? Trying to catch popping / crackling like this is just putting more transistors in jeopardy all the time the power is turned on, as well as difficult to track because the amplifier is going batsh** internally for every pop and crackle. Is it the particular transistor you are looking at doing this on it's own or because it was told to by the feedback system? That can be very hard to tell, even for the experienced with adequate test equipment, compound that with minimal equipment and an inexperienced eye giving printed verbal responses.

Six transistors on the same board.

Yeah you got lost in the forest, when all you wanted were some pine cones...

sigh, I coulda MAILED the transistors to you already... :sigh:

 

[Uncle Bambi]

Mark,

Again, I apologize for having frustrated you. It wasn't intentional, and I'm not trying to be obtuse. It just wasn't clear to me that those transistors were being pinpointed as the probable fault. It was my (apparently wrong) inference that you were specifying their replacement as a preemptive measure.

I've ordered the transistors today. and will replace them when they get here. In reading other threads, I see you caution about "free-floatng" those little brown tabs that are screwed to the heat-sink before dis-assembly. I'm glad I read about that.

I looks like the correct way to get at the backside of AWH031 would be to free the heat-sink from its frame, free the board from the frame, remove the frame, and then gently rotate the heat-sink over the top and to the front side of the circuit board. Any cautions there?

Now - reading back, you mentioned that more discussion would be necessary for correct placement. Should we have that discussion now, or when the parts get here? I'm assuming that what needs to be discussed is the CBE/BCE orientation of the old transistors, as opposed to the ECB orientation ont he new ones.

Also - remember when you warned me against NTE, and I didn't understand? Thanks for that heads-up. I went to the local parts supplier, and NTE all over the place. Thanks for keeping me out of that.

We HAVE isolated it as closely as possible for this situation, the fault IS the transistors I recommended, the 1451's with a smaller probability of the 2sa726's also being faulty.

You want to try to catch the exact one of the three in the act, or just replace them with under 2 bucks worth of transistors and have the problem go away? Trying to catch popping / crackling like this is just putting more transistors in jeopardy all the time the power is turned on, as well as difficult to track because the amplifier is going batsh** internally for every pop and crackle. Is it the particular transistor you are looking at doing this on it's own or because it was told to by the feedback system? That can be very hard to tell, even for the experienced with adequate test equipment, compound that with minimal equipment and an inexperienced eye giving printed verbal responses.

Six transistors on the same board.

Yeah you got lost in the forest, when all you wanted were some pine cones...

sigh, I coulda MAILED the transistors to you already... :sigh:

 

[markthefixer]

frustration from non karma origin, sorry it snuck out.

guys, help him out, it's been a rough day and I am falling asleep at the keyboard. several of you have btdt on yjese matters.

need to recognize symbol, look at datasheet for new tratnsystor layoit amd ignore old transistyor layout.

 

[goat67]

frustration from non karma origin, sorry it snuck out.

guys, help him out, it's been a rough day and I am falling asleep at the keyboard. several of you have btdt on yjese matters.

need to recognize symbol, look at datasheet for new tratnsystor layoit amd ignore old transistyor layout.

Mark

I can step up and help out a bit.

John I think you understand what you need to do when replacing the new transistors.

Now - reading back, you mentioned that more discussion would be necessary for correct placement. Should we have that discussion now, or when the parts get here? I'm assuming that what needs to be discussed is the CBE/BCE orientation of the old transistors, as opposed to the ECB orientation ont he new ones.

I looks like the correct way to get at the backside of AWH031 would be to free the heat-sink from its frame, free the board from the frame, remove the frame, and then gently rotate the heat-sink over the top and to the front side of the circuit board. Any cautions there?

What is going on is the lead arrangements are different so you need to
get the pin outs from the new transistors and just make sure you install them
with the leads going to the proper location.

As far as gaining access to the board.

I can not tell you for sure here but common sense is all that is needed.
Your goal is to gain access to solder in the parts without removing any wires.

So it may be necessary to loosen re route the wires that are attached to the board.

If I was doing this I would also replace the caps on this board so I would only have to do it once.

Have you made a Dim Bulb Tester Yet? If not then search for posts on how to do it.

All it is is a fixture that allows a 100 watt bulb in series with the AC input voltage.

If you have any other questions just post

 

[Uncle Bambi]

If I was doing this I would also replace the caps on this board so I would only have to do it once.

Ya know..... I thought about this after I ordered the transistors. I started trying to cross the caps, but ran into a bit of trouble.... here's what I have so far - I'd love some assistance with the top four, and maybe a vetting of the one's I've chosen:

power amp
awh-031 c1 1 25 cssa
awh-031 c2 1 25 cssa
awh-031 c3 0.47 25 cssa
awh-031 c4 0.47 25 cssa
awh-031 c7 33 16 cea 330p 16 647-UPW1C330MDD
awh-031 c8 33 16 cea 330p 16 647-UPW1C330MDD
awh-031 c11 330 10 cea 331p 10 647-UPW1A331MPD
awh-031 c12 330 10 cea 331p 10 647-UPW1A331MPD
awh-031 c13 100 50 cea 101p 50 647-UPW1H101MPD
awh-031 c14 100 50 cea 101p 50 647-UPW1H101MPD

Have you made a Dim Bulb Tester Yet? If not then search for posts on how to do it.

Check. I'll go to the hardware store today and get the necessary parts.

Thanks so much!

 

[PacificStereo]

Mark, are you sure it's batsh**? Cause I always thought it was apesh**. <big grin>

 

[goat67]

Ya know..... I thought about this after I ordered the transistors. I started trying to cross the caps, but ran into a bit of trouble.... here's what I have so far - I'd love some assistance with the top four, and maybe a vetting of the one's I've chosen:

power amp
awh-031 c1 1 25 cssa
awh-031 c2 1 25 cssa
awh-031 c3 0.47 25 cssa
awh-031 c4 0.47 25 cssa
awh-031 c7 33 16 cea 330p 16 647-UPW1C330MDD
awh-031 c8 33 16 cea 330p 16 647-UPW1C330MDD
awh-031 c11 330 10 cea 331p 10 647-UPW1A331MPD
awh-031 c12 330 10 cea 331p 10 647-UPW1A331MPD
awh-031 c13 100 50 cea 101p 50 647-UPW1H101MPD
awh-031 c14 100 50 cea 101p 50 647-UPW1H101MPD

Check. I'll go to the hardware store today and get the necessary parts.

Thanks so much!

The information about determining what caps you need to use has been discussed many times.

Search for the threads containing Pioneer Tuning Fork these threads are the
best info out there regarding the components and specs used in Vintage Pioneer Gear.

Mark is a firm believer in teaching people to fish, by me giving you this info you actually are the one that loses.

I will go look them up and give you Mouser part numbers.


A HINT
cssa caps are replaced with a film cap or a low leakage cap UKLs

 

[Uncle Bambi]

The information about determining what caps you need to use has been discussed many times.

Search for the threads containing Pioneer Tuning Fork these threads are the
best info out there regarding the components and specs used in Vintage Pioneer Gear.

Mark is a firm believer in teaching people to fish, by me giving you this info you actually are the one that loses.

I will go look them up and give you Mouser part numbers.


A HINT
cssa caps are replaced with a film cap or a low leakage cap UKLs

So this being said THIS POST IS NOT DONE UNTIL THIS LINE IS GONE

OK - I'm good with the fishing concept. I'll go do it.

Here's the thing, at first blush, when I'm trying to use the mouser search engine for the two cssa caps in question - I don't find any UKL's or film caps that match up.....

For example, c1 1 25 cssa. By definition (assuming I've absorbed your information correctly), I need either a UKL or film cap for a replacement. When I use the search string "1uf 25v" "in stock", and "capacitor", it boils down to 3 leaded electrolytic capacitors (none of which are Nichicon UKL’s), and 2 film caps, both of which are .1uf - not 1uf.

Is the solution then to up the voltage rating to 50v? If so, I come across this:667-ECQ-V1H105JL5.

Similarly, for c3 0.47 25 cssa, I find no suitable caps when searching with ".47uf 25v". But, I do for ".47uf 50v":
647-UKL1HR47KDDANA (electrolytic)

And four likely choices for film:
667-ECQ-V1H474JL3
667-ECQ-V1H474JL
667-ECQ-V1H474JLW
667-ECQ-V1H474JL5

But - when I do a "compare", they show identical specs, except for "packaging". So - Which one of the four to choose? Dunno....time to go fishing.

As an aside, I assembled and tested my Dim Bulb tester today. Works great.