My SA-9800

My beloverd SA-9800 'popping'

Hi guys. I would firstly like to commend everybody on what absolute gold mine of info this place is, especially on old Pioneers. So inspiring was it all that it motivated me pull out and fire up my old SA-9800 that my father had purchased form an op-shop ten years ago for the pricey sum of $110Au.

Now on to the amp's issue. It has the dreaded 'popping' sound in the left channel which only very occasionally sends the amp in to protection mode (usually when cold). After applying Deoxit to all of the switches suggested here it still was popping. I've narrowed it down somewhat to the power amp stage using the preouts on my current Pioneer AVR. I can also recreate the symptom by tapping or blowing air onto the left amp board (pictured). The speaker selector is quite loose, it looks as though it's just the bolt under the fascia. However taping the loose selector also makes it 'pop'. It also looks to have been worked on at some point in it's life albeit rather poorly. Note the slightly melted cables and capacitor added to the wrong side of the pcb in the second picture.




So I guess my question is, where do I go from here? I have basic soldering skills and have downloaded the service manual (US version. Couldn't find a 240v one) but am not confident following schematics.

Thanks in advance
Cal

Hello Cal....I am having a few problems with my sa9800.......could you in any way post a high quality picture of the bottom of the amp....without the cover on ofcourse....I need it for comparison purposes........

Mine is having some kind of power board issue...blew a couple of fuses......I managed to get the amp back to life after changing the fuses...........

You need to get at the solder side of the left channel (popping channel) amplifier board and look for cracked solder joints, starting with the driver transistors (a913,C1913) with the u-shaped heat sinks attached.

The solder cracks, and not just on the driver transistors. When the boards were wave soldered, the solder could be very thin and prone to cracking. Heat cycling and age do the rest.

IF you find one, there will be others, I routinely resolder these boards, that being faster than trying to find an intermittent cracked joint..

Visually they will be hard to find, but if you move the component it will be evident.

BE CAREFUL FOR THE BIAS DIODE (STV-2H) WIRED TO THE AMPLIFIER BOARD BUT MOUNTED ON THE BIG HEAT SINKS. The leads love to break off at the horseshoe shaped body, so do NOT flex them near the component!!!

Mark I can't thank you enough!

I finally got an afternoon off and decided to give it a go. Looks as though you pin-pointed the problem without even seeing my amp! I re-melted the solder on the driver transistors and it seems to have fixed it. I realise I should have resoldered but space was really tight and didn't want to push it after you warned me of the break prone leads.

anderslober: Not sure if you still need them but I've attached some pics of the bottom of the amp. They're pretty big so I've linked them.

Bottom of Amp 1

Bottom of Amp 2

Thanks again Mark :thmbsp:

Hello fixed term.....those are graet pictures...many thanks. My amp is a little bit different....yours has 4 fuse positions, mine has just 2. Otherwise they look very similar.,.....which is good news to me.

I can also see, that your right channel has had 2 output transistors changed....does this in any way affect sound?

Again,...thanks a lot for the fotos......a big help.

These are the stv-3h and stv-4h etc parts to be careful of, they are the repaired (top) and original (bottom) stv-3h or stv-4h diodes (h=horseshoe):

Hey guys

I really haven't noticed any difference in the sound quality with regards to the output transistor. I have however considered changing them all over to matching items to put my mind at ease, though if it ain't broke......

Another question I needed to ask is - I'm getting quite a lot of noise when using the SA-9800 as just a power amp. I don't seem to get this noise when its used normally, plugged directly into a component (cd, tuner etc). It doesn't seem to be coming from the pre-amp either as I tested the output with a different power amp. Could this be a grounding issue of some type?

Cheers
Cal

anderslober said:

Hello fixed term.....those are graet pictures...many thanks. My amp is a little bit different....yours has 4 fuse positions, mine has just 2. Otherwise they look very similar.,.....which is good news to me.

I can also see, that your right channel has had 2 output transistors changed....does this in any way affect sound?

Again,...thanks a lot for the fotos......a big help.

Click to expand...

In this type of amp (NSA), it's a good idea to keep the outputs matched and fast to minimize distortion, what are they?

I'm not too sure mark but they can be seen in the one of the pictures I posted

Bottom of Amp 2

fixed-term, the output transistors (2sa1492) are replacements and not really ideal. Not only that, you have non matching NPN and PNP pairs now. The RETs Pioneer used are generally complete crap after 22 years and you are better off to get them all replaced or at least removed, checked and new thermal compound done. The 2SA1078 is the correct transistor that should be there- but I'd get them out. What's on the other side?
The base of the filter cap/bridge board looks like it has been attacked, and several wire wrap points on the Power supply board have been soldered over the wire wrap. I would be removing the AWR196 power supply pcb and desoldering/resoldering all the high temperature areas (the darkend parts). The PSU board is the second iteration, where Pioneer added a second set of regulator transistors as the old ones (the early multi models) blew up too often.
The other thing you should check is the DC rail voltage on the caps- they are 71 volt caps and they often sit at 78volts on the 240volt units. I have found Pioneer mixed up the 220/240 volt tappings on a few.
All in all, they are a wonderful sounding amplifier, but Pioneer should be shot for the design- wire wrapping springy thick guage wires to poorly soldered PCB pins, putting a regulated heat producing power supply under the transformers with no air circulation, using a beautiful symmetrical power amplifier amplifer design and then sticking RETs on the end of wire wrapped pins, soldered to another pcb and wire wrapped as well and jamming it all under the heatsinks and hoping for reliability!
I love the big Pioneers, but these babies must be very thoroughly gone over if you want reliability.

The protector board has also been attacked- notice the resistor and cap on the track side and the usual melted wire sheath from yet another dodgy 'technician' who couldn't solder properly.