pioneer sx1080 help...

[gene french]

in addition to the phase linears...i have a 78 model sx1080...at first it started cutting out...going silent...i blamed it on my internet...then i discovered that was not the problem...it would shut down the come back on...over time the cutting out came more often and the coming back on took more and more time...i did accidently short out something i should not have trying to read my dvm in a tight place...make a long story short it is back up and running...after changing a few parts...
only one problem left to conquer...
when the stereo/mono switch is in the stereo position...no right channel...only left wattmeter registers...balance will silence left side when rotated to right side...
when the stereo/mono switch is in the mono position....both channels make sounds...both wattmeters register...balance performs as normal...
i would appreciate any insight on this...
btw...i did successfully change out all output transistors with 2sb755s and 2sd845s...was able to set the center voltage and idle current correctly...
hoping i am at the end...
thanks in advance
gene french

 

[J!m]

Check my sx-880 restoration thread for some ideas.

 

[George S.]

I'd be looking for a dirty stereo mono switch, broken wire in that circuit, or poor solder joint in that circuit. First check the switch with the wiring disconnected from one side hopefully from a connector at a circuit board.

 

[J!m]

I don’t think those exist in these. Switches are soldered direct to the board.

A good cleaning of the switch is in order- D100, but pots get fader lube/cleaner ONLY.

I just brought my 880 on line today.

 

[gene french]

good place to start tomorrow morning...
i slept most of the day away today....
lol
thanks you guys

 

[markthefixer]

The block diagram in the service manual is your friend.

A good cleaning and deoxiting of the TAPE switches is needed because the audio is switched by them even when tape is off.
They get their input from the FUNCTION switch.
The TAPE switches send their audio to the actual start of the active electronics - first the balance control then the volume control and then ... transistors....

The thing to remember about the mono switch is that it is the only "fail safe" switch in the unit.
If the mono switch fails, the signal stays stereo and cannot be interrupted.

What you are hearing when the MONO switch is on, is the left channel in the right channel, as well as the left channel in the left channel.



And, yeah, you saw this and me on audiokarma pioneer audio forum.

 

[laatsch55]

School em up Mark!!

 

[gene french]

yes...i need schoolin...led zeppelin...
i was wrong in a way....i am testing behind a dim bulb tester and had volume turned down...
when i turned the volume up....i had sound on the right channel.....just low volume...
pin 10 on both amp boards are a little less than 10mv...i understand this is about normal...
i need more schoolin...gene french...
lol

 

[gene french]

and from the bottom of the unit...i did check continuity of the switches with my dvm...
all switches are functioning as expected...i cleaned them a while back with contact cleaner...
and i will do so again before i button it up...if i can get past this problem...
thanks guys...i do appreciate...

 

[gene french]

i have a preamp here that i use on the phase linears...
what if i plugged the output of the preamps into the amp input section of the 1080...
would that tell me anything???

 

[gene french]

The block diagram in the service manual is your friend.

A good cleaning and deoxiting of the TAPE switches is needed because the audio is switched by them even when tape is off.
They get their input from the FUNCTION switch.
The TAPE switches send their audio to the actual start of the active electronics - first the balance control then the volume control and then ... transistors....

The thing to remember about the mono switch is that it is the only "fail safe" switch in the unit.
If the mono switch fails, the signal stays stereo and cannot be interrupted.

What you are hearing when the MONO switch is on, is the left channel in the right channel, as well as the left channel in the left channel.

View attachment 63725

And, yeah, you saw this and me on audiokarma pioneer audio forum.

thank you so much...i need all the help i can get...
i need schoolin...

 

[gene french]

i have a preamp here that i use on the phase linears...
what if i plugged the output of the preamps into the amp input section of the 1080...
would that tell me anything???

ok...problem is definitely in the preamp section....preamp out from the preamp into the amp in on the sx1080 produces great music...
problem definitely in preamp section...
see....i am making progress...lol
please suggestions????

 

[WOPL Sniffer]

Time to hit that schematic

 

[markthefixer]

still block diagram time.

Preamp trouble, ok

Set it on MONO, so we know both channels have exactly the same input.

just for grins, fool with the BALANCE control a bit
just for grins, fool with the VOLUME control a bit
just for grins, fool with the LOUDNESS switch a bit
just for grins, fool with the MUTING switch a bit

turn on and off the tone control - what happens- operate the switch a few times, any change?
(if it's the tone control, we'll come back to those switches and pots)
turn on and off the 15 Hz filter - what happens - operate the switch a few times, any change?
turn on and off the 6 KHz filter - what happens - operate the switch a few times, any change?




'

 

[gene french]

ok...i did it...but i wasnt grinnin...lol
when i first had trouble and removed the case...i saw a bloated cap in the power supply section...so, i recapped...in november...did not resolve the issues beginning to manifest themselves...i got worst until it quit...
at that time....i cleaned all pots, switches with contact cleaner, when i had easy access to them...
this morning...i pinned out the switches on the flat amp board...all performed as expected....in the mono mode the balance works as expected...
the tone switch as well as the tone controls all performed as expected....just no right channel in stereo mode...
when i plugged in my preamp into the amp in on the sx1080....it played both channels...
not sure if this is related, but since i have owned this...the am radio emits no sound either...i did not worry about it, because i dont listen to am radio...
i appreciate the help very much...
i am trying hard to learn...
gene french

 

[markthefixer]

What I posted is all part of a methodical exploration of the problem.

there are only 3 transistors per channel in the preamp.
there is a jfet that rarely causes problems,
a 2sa726
and one transistor that's part of the tone amp. which you ruled out.

Jumping ahead a bit, letting experience listen, then talk, the flat amp has the 2sa726 transistors on it - we call them "shoot on sight"....

while our standard replacement is a ksa992 transistor
specs: (512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe)
I have little idea of what is plentiful in your area that will work.

FM works? Am doesn't.... interesting...

 

[gene french]

if you are referring to q3 and q4 on the flat amp board....the recap kit included 2 ksa992 transistors...along with the data sheet...
i did not use them...the originals tested good in circuit...and by tested good...i used the dvm in the diode mode....and double checked with an analog meter .... but, in circuit...i did not remove them for testiing....

 

[gene french]

What I posted is all part of a methodical exploration of the problem.

there are only 3 transistors per channel in the preamp.
there is a jfet that rarely causes problems,
a 2sa726
and one transistor that's part of the tone amp. which you ruled out.

Jumping ahead a bit, letting experience listen, then talk, the flat amp has the 2sa726 transistors on it - we call them "shoot on sight"....

while our standard replacement is a ksa992 transistor
specs: (512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe)
I have little idea of what is plentiful in your area that will work.

FM works? Am doesn't.... interesting...

what does shoot on sight mean???....common problem possible...
yes, am has never worked since i got the box...the signal meter shows it is receiving a signal....but, not proceeding any further...
never really worried too much about that one...but, now that i am elbow deep in this thing.....just something else to track down...
i really want to make the big boy club!!!!

 

[J!m]

For the AM problem, I’d be looking at that selector switch first. Especially if the meter is showing signal. (Although I don’t know what the flow order is for signal)

 

[Gepetto]

what does shoot on sight mean???....common problem possible...
yes, am has never worked since i got the box...the signal meter shows it is receiving a signal....but, not proceeding any further...
never really worried too much about that one...but, now that i am elbow deep in this thing.....just something else to track down...
i really want to make the big boy club!!!!

It means this Gene...

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