SA-7500II recap

loweran

loweran

Super Member
All,

I am starting to put a list together for an SA-7500II. This is a working unit and sounds pretty good as is.

So, the question is, should I just replace the top 10 worst list of transistors in the unit which are only two 798s or should I target more? Also, if the power is good, should I still replace the diodes?
 
I have the mk1, if the unit is working fine and the voltages are on spot I would let them alone. I really like this silver amps.
C0g and PP caps on signal path made a good improvement on mine
 
Yes sir always do when messing around with one of these.

I’ll look and see what I have and may go ahead and order replacements just in case. They are cheap enough. I have been ordering more than I need so starting to have a bit of stock.
 
Parts should be here tomorrow. May get some time to dig in. I opened it up and it looks like everything is easy to get to. I validated all the e-caps to be as documented in the SM.

Couple of questions:
Not sure how to, or if it's required to, re-grease the outputs.
Looks like the filter caps are multi lead (5?). Anyone know how to convert the 2 lead caps to match?
SM does not list pin voltages for power and amps. They list transistor voltages.
I will be replacing the two 2sa798s with pairs of ksc992s I ordered a cheap meter with hFe feature. I assume that will be good enough to match the ones I have. I did try the diode measure on EB and CB on the ones I have and they are all the same.

Any other notes that I should be aware of?
 
I am interested in your parts list. I have an SA-7500ii as well. I have several other Pioneer pieces which need to be checked.

As much as I've searched this site I am still not certain I have found the definitive recap lists. Marty Socal, markthefixer and mattsd have all contributed.
The AK database for Pioneer doesn't seem to get updated. The Pioneer Recap STICKY seems iffy. Mattsd has contributed a bazillion brain droppings across the site. Maybe it's time for a Moderator to become involved? Would it be possible to create a sticky or use the document database for definitive lists to which only a few members could contribute? Start by pulling the most current versions of recap lists into one place and freezing the old, lengthy threads? I'll forward this post to a moderator. Not certain if I'm overstepping boundaries here. If so, my apologies.
 
loweran,

I recently completed a restore on my 7500 II. I did not bother to re-grease the outputs on mine so can't comment on procedure. The original filter caps are multi lead but only 2 leads are actually connected to solder traces, the others are just used for stability. I also did not replace the 798's since the measured offset was well within tolerance and equal on both channels. If you do decide to replace with the 992's you will notice the board will have the extra hole so you will not need to double up the emitters.

When I first received my 7500 it was going in and out of protection. The problem was narrowed down to the protection relay driver transistors being faulty. Sorry I didn't make up a BOM for this unit when I did mine.
 
One thing I forgot to mention...Pay careful attention to the orientation of caps C23 and C24 (2.2uf 50V). The originals on my amp were installed with reverse polarity than the schematic and screen print. Since I couldn't get a definitive answer on which was correct, I elected to install bipolar caps in those locations.
 
Cuppy said:
One thing I forgot to mention...Pay careful attention to the orientation of caps C23 and C24 (2.2uf 50V). The originals on my amp were installed with reverse polarity than the schematic and screen print. Since I couldn't get a definitive answer on which was correct, I elected to install bipolar caps in those locations.
Click to expand...

Good call. I will pay close attention. I did go through and spot check most of the caps to the documentation to see if they matched. Cant always see the screen print under the cap. Mine is a working unit and untouched. I will put them in the way they came out.
 
Just as I suspected. Since I never received a definitive answer as to whether it was an error with the SM and silk screen or an error with the factory install, I decided to replace with a bipolar so it wouldn't matter. May not make any difference since it worked before the recap from the factory. Wish I knew/understoold more about the design if the circuit.
 
Here is what I have found so far:

C23 and C24 installed opposite of the SM and silk screen
R91 - 680 2W looks burned
R51 150 .5W looks burned
R97 270 .5W looks burned
R52 150 .5W looks burned

Lots of cold solder joints

Repair work done prior
Q15 replaced
Q11 replaced
D9 replaced
R97 replaced
Q5 replaced
 
Done with the caps except for the filters. Did not do the transistors yet since I don't have my meter. Left channel reading 30mv. Right channel reading 15.5mv
 
Damn, the filters I have don't fit and too big to stuff the can. Wonder if I can mount them off the board and use wire. Thoughts?
 
Here is a pic because I like pics.
 

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loweran,

I just posted this pic in your other thread regarding the filter caps.

recap.jpg
 
Got them wired in. Got some 14awg solid 300V wire and wired them up. Worked great.
 

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Sounds pretty bad. I have 60VDC on the right channel speakers and 23VDC on the left. Voltages at the transistors seem off. Going to have to investigate. I noticed a couple of resistors looked burned as listed above. May start there. Probably going to need to replace some transistors too.
 
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