SX-828 random periodic loud crack or pop

id78

id78

New Member
Hey.
Tried and failed to resurrect old thread:
http://audiokarma.org/forums/index....assive-pop-when-low-filter-is-flipped.588093/

Reposted here:
Thank you, ahead of time!

problem description almost matches an issue I have
with my otherwise very lovely and beloved 828.

Periodic, random loud crack/pop.
Volume up or down.
Sitting at idle, no load on it.
Other than that, heh, she is fine.

Same possible source?

Q?
"Coupling caps" described above are on which board?
Schematics of Tuner and AF Unit show cap numbers that go that high.
Thanks again!
Jimmy

UPDATE: Other Post appeared under DIY.
Sorry about the double post.
L.
 
Last edited:
you have a bunch of transistors to replace: 2sa725, 2sc1312 in af amp, 2sa726 in the main amp.
the 2sa725, 2sa726 get ksa992, the 2sc1312's get ksc1845's.
plenty of old electrolytic caps to replace as well, but the pops are from the 725's in the af amp AFTER the volume control. eventually they will fail completely, and can do more damage.

others can help you down this path, I'm just pointing the direction.
 
If you have another power amplifier for the purposes of your immediate problem you can isolate what "stage" your problem is at.

Connect another power amplifier to the "pre out" outputs of your unit. Then run an ipod or something with a signal source at low volume directly into the "main in" sockets on the back of your unit. See where the problem remains. It will generally be in the "pre" or the "power" sections of your unit.
 
In addition to the problem children Mark the Fixer Listed, There are in the HEAD AMP BOARD (W21-002) either 2sc871 or 2sc458. Replace them with KSC-992(EDIT 4-19-17. CORRECT ITEM IS KSC1845. The KSC992 is a TYPO!!!!) . These are also problem children, actually one of the1st transistors to coin the term. Replace any that are found on any board!

On the AF Unit board(AWK-012) there are (2) 2sa725 and (4) 2sc1312. Replace. DO NOT TOUCH the 2SK30's upon pain of Death. These are practically unobtainable, and usually replaced with a replacement that is questionable at best.

On the Main Amp board(AWH-010) there are no known problem children.

When you list a board by name, also list the board number on the unit. It will be in a rectangular painted box, with a stamped number in it. Write down the complete number INCLUDING
any SUFFIX letters. You'll note that I listed the board numbers off the manual so everyone who is using one to follow along is on the same page.
So just replace the 2sc458/2sc871s on the Head amp (also known as the phono preamp), and the 2sa725/726 and the 2sc1312's on the AF UNIT BOARD( also known as the tone control board/ or main preamp).

NOTE: the 2sa725 and 726 are lumped together as they have virtually identical specs. Basically kissing cousins if you will. They both get replaced with the KSA992.

2nd NOTE: NEVER get transistors from EBAY. Too many cases of fake transistors. Get them from Mouser or Digikey. Guaranteed to be the real thing and cheaper to boot.

3rd note: Download the Datasheets with the transistors for the leg pinouts. 99% of the time (with the exception of 1 or 2 types) the leg pinout WILL be different than the original transistor. So some creative leg bending may be needed.
 
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Teardown for 3 new dial fuse/lights
only took about 6 minutes.
Thanks to Larry de Rouin for this:
http://imgur.com/a/lvTCL

What amazing execution, attention to detail..
Magnificent piece of work.

*********
The original CRAAAK or POP happened
a second time, a few years ago,
Shut her down and put aside till now.

So far, not replicating the issue.
There is a mild pop coming out of the low filter, while powered up.
So I am not going to do that again.

Running low volume, radio feed.

Do I need to check each path/source?
"Probably" would be my WAG.

So far, she is happy gal.
*
Perhaps upset about her face?
What supermodel likes poor lighting?

Although I have come to suspect these things
do not really work that way.
Will update.

And thanks to all.
This sort of thing is the best of the web, in my view.
Makes me grateful to live during this amazing era.

*****
 
Okay.
more data:
Right is okay out A,B,C.
Left is okay out of C.

Left out A
Volume at zero, power up
...click goes the relay...
BOOMINSTAVOLUME,


Left Out B.
same start.
No Big Bang, in fact no real signal.
spacey shwooshy sound


Time machine setting?
 
id78. Correct spelling is Derouin, although some of my french speaking ancestors (15th or 16th century) spelled it de Rouen or de Rouin. Derouin is one of about a dozen variants of de Rouen (from Rouen, France). I had French Canadian Nuns in Catholic School in Connecticut back in the early 60's. They insisted that the way I pronounce is was WRONG and that I was to pronounce it as the French pronunciation. The problem ended up on the Bishops desk and I ended up winning as 1.) This was America, Not France. 2.) My Great Grandfather changed the pronunciation to the present "DER-RON" as he felt that it was more American, than "Dair-oo-ween" as the nuns pronounced it. The Navy weighed in on it too as they were bussing over half the schools population from Navy Housing at the time. I didn't get called on too much for the rest of the year. And when I did it was always, "YOU" with the funny French Name"! I'm used to people butchering it now.
 
Projected my own Canadien roots
and genuine fondness for Fr. there.
One great guy I knew, last name Jacques.
Jake. His entire life.
Bothered him, but he just accepted it.
Mostly.
But it always rattled his ears.
*******

Ok, I am here:
"So just replace the 2sc458/2sc871s on the Head amp (also known as the phono preamp), and the 2sa725/726 and the 2sc1312's on the AF UNIT BOARD( also known as the tone control board/ or main preamp)"
***

828 Head Amp Unit (W21-002)
828 AF Unit AWK-012
Not hard to find, marked with red arrows, check?

http://imgur.com/a/lvTCL

AF is hard to get at though.
Can the new bits be mounted to the bottom of the AF Unit?
 
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Yes and no. Yes in that they could if you positively identified each and every leg correctly, and no in that the metal shield on it (as shown) would not fit. Best way is to take off the front panel, and disconnect all of the switches and pots from the inner panel, then slide the board out toward the rear and replace parts as original. It's a Pain in the a**, but doing it right the 1st time prevents mishaps later down the road.
 
Hey zebulon, nice van!

Okay, double checking:
AF Unit
(2) 2sa725 get ksa992
(4) 2sc1312 get ksc1845

Head Amp unit
(6) 2sc458 get KSC1845.

Larry, there actually is no shield on the AF Board.
Do you refer to the bottom panel of the receiver?

I really don't want to pull that out of there.
But I will.

Probably.

Thanks again.

Ordering parts.
Will update!
*********
In the meantime, the OP-6 in my pic is still with
brother OP-7 and Daddy, an RCA 44BX.
In need of a little this and that.
This was a mobile broadcast setup, output to a landline.

They have been a trio since WWII.

Decades with me, just found out a few weeks ago,
thanks to these interwebs ...
the crazy 12 pin power connector
also handles a line from a Battery.

A Battery.

Darn things somehow run on a battery?

More digging, i guessed 6 volts, and that is it.
6 Volts.

I could see an Edward R Murrow typefellow in the bomber,
needs his gadgets to work.
crafty fellow hooking it up to a jeep battery.

The twelve pin struck me as an unusual proprietary
decision for that era, there are things inside the devices, sealed
electrical gadgets, but generally not proprietary connections, right?
Every guitar plugs into every amp, ever,
and every appliance into every home, etc.

So why the 12 pin?
To confuse the bad guys if they get a hold if it?
***
Mobile is a bit more mobile now.
Battery was 40 something pounds,
OP 6 and 7 are 20 something each, the 44 must weigh 10 lbs.

That Mic, i dropped it on my foot once.
Thought for four days I had broken
my foot.

Still Real Careful with it now.
Heh

Thanks again.
 
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