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Pioneer SA-9800 - what to do?

Since you have one good working unit, you can do nodal R comparisons of the good unit against the non-functional unit, first, with the power off of course before you un-solder anything.
The PA consists of a number of constant current sources, Q8,22,24 that are used to setup the o/p stage bias, so it is a matter of checking out all the components.
 
Alright, i should have checked once again... Q12 was installed backwards. After i checked it and installed it the right way, click and music!

I checked all the voltages and set up the right values. Then i connected the speakers and well, it hummed. Not loud but noticeable. And when i did something with the controls (volume, balance, etc.) the woofers would jump back and forth. One ground was missing. It took some time but when i finally found it i was rather stunned. Two pieces of copper trace for the ground on the tape switch was burned away. I also found that C7 had exploded. Fixed the problems and now the pumping is gone but the right channel isn't working properly. When i play through it it does play music but it also lets dc out. The higher volume the higher DC voltage.


What could cause a grounding problem that would blow C7? I would lie if i said i wasn't worried...
 

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Turns out that the speaker i used was not made for this Pioneer. Once i removed it and tried with another speaker it worked. No hum and no DC. Really weird since i used it with my Yamaha with no problem at all.

There seems to be some problem with the Phono section. At TP15,16 i have 7v DC. That's the lowest i can adjust it to so something is wrong. The positive and negative rail is present so maybe i fitted something wrong...
 
I'm stuck. There is +30 and -30. There is also ground where it should be. The transistors measure like the should but all of the voltages are messed up. 0.8 is 14v and so on. All of the values in the phono section are way out of specs. The voltages measure the same on both channels so you would think it is something common (ground or rails).
I have checked all of the capacitors with the manual so they are not the problem.

Someone have any ideas?
 
I'm not sure i get your point. The protection is fixed and tested and what would that have to do with the phono section? :saywhat:
 
What could cause a grounding problem that would blow C7? I would lie if i said i wasn't worried...
Click to expand...
The short NP ecap probably caused this.

There seems to be some problem with the Phono section. At TP15,16 i have 7v DC. That's the lowest i can adjust it to so something is wrong. The positive and negative rail is present so maybe i fitted something wrong...
Click to expand...
This is the MC phono pre- section, so I suspect you fitted something wrong, and on both channels too, it does the exact same thing which is very suspicious!! Did you change any transistors (if so, then re-check orientation) or only ecaps?

I'm stuck. There is +30 and -30. There is also ground where it should be. The transistors measure like the should but all of the voltages are messed up. 0.8 is 14v and so on. All of the values in the phono section are way out of specs. The voltages measure the same on both channels so you would think it is something common (ground or rails).
I have checked all of the capacitors with the manual, so they are not the problem.
Click to expand...
Measuring R's in the circuit can be mis-leading. The only way to test a R properly is having it isolated in other words one leg lifted out of the circuit, but it is very unusual for a R to fail in this these circuits. Better check everything again. This a very simple circuit, but other than this MM pre-amp everything is working okay?

Good Luck
Rick
 
Which NP capacitor are you taking about?

I only replaced the capacitors, did not even unsolder anything else.

I only measured the transistors in one channel but i did unsolder all of them when i measured them. And since the voltages are exactly the same in both channels, i did not bother to measure the other channel.

Everything else is working and all of the voltages are according to the manual.
 
Found the problem. Q9 and Q10 was shorted but my Fluke wouldn't tell me that at first... These are 2SA726 and i've found 2 more in the EQ. I will replace all four and it would seem that BC556 are a good substitute.
 
What could cause a grounding problem that would blow C7?
Click to expand...
I assumed you were talking about C7(4.7u/25V/NP) on GWG-124
yes, replace those pesky 2sa726, with BC556 or ksa992
My typo
This a very simple circuit, but other than this MM pre-amp everything is working okay?
Click to expand...
should have said "MC" pre
So sounds like you are back in action ...

Cheers
Rick
 
Oh, there are two C7. I meant the 1uF 50v (ground to ground) on the input board.

As soon as i get those replaced this should be in 100% working condition. Now i know what to expect when i will rebuild the new 9800. Although that will have to wait for some time since Mouser doesn't have all the parts in stock and i spent all my money buying it. At least i know that i also need to replace those 726.
 
Although that will have to wait for some time since Mouser doesn't have all the parts in stock
Click to expand...
There are usually more than one sub (more so for passives than actives), what parts are out of stock?
P.S there is also a couple of 2sa726 in the PA, Q9,10(2sa726s)
 
Which C7, on which board?

What could cause a grounding problem that would blow C7? I would lie if i said i wasn't worried...[/QUOTE]
Actually there are at least 4 capacitors labeled C7 in the Pioneer SA9800, I am unclear which is the blown C7?
GWF116 Equalizer board C7 100uf at 6v
GWG124 Control amp board C7 4.7uf at 25v nonpolar
GWH119 Power amp board C7 47pf
AWR191 Power supply board C7 47uf at 63v
 
The two 726 in the PA i replaced since they were on the recap list but i didn't myself check if there were any more transistors to be replaced. Now i know there are at least 9 of those 726 to replace and maybe something else (haven't checked all the transistors).

There are just three capacitors out of stock but one of them is those big 15 000uF. I know i can just change the capacitors and so on but i still don't have the money for it. Besides, the new one works perfectly. I even mounted a fan underneath the power supply just in case.

It's the 1uF 50v on the input terminal board. It connects ground to the terminals -.
 
Really?

Boy it is hard to conceive that the 1uf on the input board got smoked. You would not think there would be that much current!
 
It's a mystery to me. It must at least been a temporary problem since I've played with it for 40 hours with no problem or any blown capacitors.
 
Recap?

elektronror said:
The two 726 in the PA i replaced since they were on the recap list but i didn't myself check if there were any more transistors to be replaced. Now i know there are at least 9 of those 726 to replace and maybe something else (haven't checked all the transistors).

There are just three capacitors out of stock but one of them is those big 15 000uF. I know i can just change the capacitors and so on but i still don't have the money for it. Besides, the new one works perfectly. I even mounted a fan underneath the power supply just in case.

It's the 1uF 50v on the input terminal board. It connects ground to the terminals -.
Click to expand...

Did you rebuild the entire GWF116 board? I am having a lot of problems with such!
 
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