Pioneer SA-9800 restoration and upgrade

leesonic

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I thought I'd start my own thread on my on-going Pioneer SA-9800 restoration and upgrade. I bought this amp a while ago, it was missing the top and bottom covers, and three of the smaller sized knobs. I have a "wanted" ad posted on Barter Town, but so far no results.

SA-9800-01.jpg

SA-9800-03.jpg

SA-9800-04.jpg

I brought the old thing up from the holding area (basement) to the workbench (kitchen table) after everyone had gone to bed, and took some measurements. The results are interesting to say the least...

4 fuses on PSU board all good. Amp power light comes on, protection relay clicks after 5 seconds, no display. I was assuming I should measure from the pins listed to a suitable ground (like pin 8). The voltages I measured are show below in red.

pins 1&2: -6.2v, should be -52v, regulated
pins 3&4: +4.2v, should be +52v, regulated
pins 5&6: -0.3v, should be +32v, regulated
pin 7: -0.3v, should be +18v, regulated, provides power for display circuit
pin 8: 0v, ground
pin 9: raw, -75.3v, unregulated
pins 10&11: -0.2v, should be -32v, regulated
pin 12: raw, +74.6v, unregulated
pin 13: raw, +74.6v, unregulated
pin 14: 0v, ground
pin 15: raw, -75.5v, unregulated
pin 16: +6.6vac
pin 17: +56.6vac
pin 18: +56.5vac

Looks like mine is losing power somewhere. There was a red 2.2k resistor, I believe it was R5, that was getting hot.

In addition, while probing around the board, I measured 165v AC between the positive of C2 and the ground. How is this even possible? The capacitor is only rated at 80v. I was so surprised, I got another meter, an old analog one this time, and measured it again. Same voltage.

Lee.
 
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huge cap voltage is measurement artifact, generally that calls for a series 0.1uf cap to block the dc and read only the ac,

other readings say all of psu is toasted.
 
It's ALIVE!

Well, kind of...

I replaced all the electrolytic caps on the power supply board, the four rectifier diodes, two zener diodes, and all the transistors apart from the 2SK34s (I have some on order, but they're taking forever to get here). I also replaced all the resistors with 0.6w 1% metal film, except where higher wattages were needed while I was at it. Some people might question why, but I did actually find two resistors that were totally open circuit without any indication that they had failed, no burning or discoloration.

Places where things looked hot, like the zener and 330ohm resistor at one end of the board, I mounted these components off the board a little so some air could circulate around them.

After double checking my work, I powered it up, and lo and behold, the display lights up. Only thing is now, the protection relay doesn't click in now. Ho hum, I will check and see what voltages I'm getting on the supply board when I get a chance.

SA-9800-05.jpg

SA-9800-06.jpg

SA-9800-07.jpg

SA-9800-08.jpg

SA-9800-09.jpg

Lee.
 
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Wow lee, I can't believe you swapped out all those resistors. Between your thread and solutionroom's making my own thread is pointless at this point. Suffice to say i'm interested to see how yours turns out. My power assembly board has the exact same scorching...in the exact same places. Power on, relay-click no display. I just finished re-tran'sing the the power and protection board and new caps. I couldn't find SK34's to save my life. If you bought extra I would gladly pay for a couple.

As to your protection relay issue....just going by your photo's and comparing to my own unit. I see a couple things.

1. Picture 2, Top Left Pin 6 appears to no longer have your blue wire connected and I can't tell from the picture but it almost appears the yellow wire is connected to six and it should be connected to 5 based on your original photo(confirmed on mine as well)

2.Picture 2 and 3, Pins 25-27 and 30 and not shown connected. I removed these wirewraps on mine to get the board out to a suitable angle to work on. Did you re-attach them as I believe that pin 30(thin yellow) goes over to the protection circuit.
 
Nice! Make sure those sk34s are legit. There have been issues with them being branded (labeled) correctly. You using a DBT? Mine struggled to power up properly even with a higher wattage bulb. Good move doing the resistors.
 
I couldn't find SK34's to save my life. If you bought extra I would gladly pay for a couple.

As to your protection relay issue....just going by your photo's and comparing to my own unit. I see a couple things.

1. Picture 2, Top Left Pin 6 appears to no longer have your blue wire connected and I can't tell from the picture but it almost appears the yellow wire is connected to six and it should be connected to 5 based on your original photo(confirmed on mine as well)

2.Picture 2 and 3, Pins 25-27 and 30 and not shown connected. I removed these wirewraps on mine to get the board out to a suitable angle to work on. Did you re-attach them as I believe that pin 30(thin yellow) goes over to the protection circuit.

I'd be interested in your resistor list for the power board lee, for future reference.

I found my 2SK34s on eBay, but I ordered them two weeks ago and they still haven't arrived. I e-mailed the seller, because it doesn't take two weeks to get from NY to NJ. Still running the original 2SK34s.

Well spotted on the wires, but I took the picture before I hooked everything up. The yellow is connected to pin 5 not 6, and the blue wire broke off pin 6. Pins 25-27 and 30 got reconnected in order for me to measure voltages. I changed out the 2.2k resistor for a higher wattage one, but it still gets warm. I didn't measure the voltage at pin 30 yet, I wonder what it should be?

What I did notice is the two transistors on heatsinks are getting very warm. Why don't manufacturers put bigger heatsinks on them, sometimes it seems like the smallest piece of metal will do. Plus the board is mounted upside down on the bottom, so there is nowhere really for the heat to go. I might try making up some bigger heatsinks from some pieces of aluminium I have in the garage.

As for the resistors, I used whatever 1% 0.6w ones Mouser had in stock. I had to use two different brands, as some of the lower values were not available in one of the brands. I can post part numbers if you really want, no problem.

Nice! Make sure those sk34s are legit. There have been issues with them being branded (labeled) correctly. You using a DBT? Mine struggled to power up properly even with a higher wattage bulb. Good move doing the resistors.

I'm afraid I'm using a SOTP (Seat Of The Pants) instead of a Dim Bulb Tester. As I said above, the 2SK34s are coming from an eBay seller, but if the power supply works at the moment, maybe I'll keep the originals.

Lee.
 
SOTP is very risky. Especially on this type of unforgiving amp circuit (NSA). And I'd be VERY concerned about those SK34s being genuine, especially off Eprey from a seller reluctant to ship or communicate. There are all kinds of fake transistors around. I'd keep the originals in as you suggested.
 
As for the resistors, I used whatever 1% 0.6w ones Mouser had in stock. I had to use two different brands, as some of the lower values were not available in one of the brands. I can post part numbers if you really want, no problem.

I would if you have them on hand.

I powered mine up last night on variac. Replaced all the caps, all transistors EXCEPT 2sk34's(originals were fine), and 2 of the 3 zener's. Also did the caps and transistors on the protection board.

Powered on...display lights....5.4.3.2.1..click. We have a heartbeat. Hooked up some speakers and sounded pretty good. I'll check the voltages today and see what pin 30 is.

Did you replace any components on the protection board? If it worked before you did the power assembly work then my instinct says its something simple your overlooking when you re-assembled. The action of bending over the power board to get a suitable angle to solder stresses those wire wraps all along the bottom. I've found that when those suckers decide to break they like to do so at the very bottom of the wrap and aren't always obvious. Double check all of those.
 
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I'd be interested in your resistor list for the power board lee, for future reference.

I'll check the voltages today and see what pin 30 is.

OK, I did some nifty cutting and pasting from my order, and here's the list, sorry for the delay.

Mouser #: 71-CPF22K2000FKE14 Desc.: Metal Film Resistors - Through Hole 2watts 2.2Kohms 1% 100ppm
Mouser #: 594-5093NW2K200J Desc.: Metal Film Resistors - Through Hole 3watts 2.2Kohms 5%
Mouser #: 71-CPF2-F-330 Desc.: Metal Film Resistors - Through Hole 2watts 330ohms 1% (2 of)
Mouser #: 271-1.8K-RC Desc.: Metal Film Resistors - Through Hole 1.8Kohms 1% 50PPM
Mouser #: 271-33K-RC Desc.: Metal Film Resistors - Through Hole 33Kohms 1% 50PPM (2 of)
Mouser #: 271-22K-RC Desc.: Metal Film Resistors - Through Hole 22Kohms 1% 50PPM
Mouser #: 271-5.1K-RC Desc.: Metal Film Resistors - Through Hole 5.1Kohms 1% 50PPM (3 of)
Mouser #: 271-5.6K-RC Desc.: Metal Film Resistors - Through Hole 5.6Kohms 1% 50PPM (2 of)
Mouser #: 271-12K-RC Desc.: Metal Film Resistors - Through Hole 12Kohms 1% 50PPM
Mouser #: 271-1K-RC Desc.: Metal Film Resistors - Through Hole 1Kohms 1% 50PPM (2 of)
Mouser #: 271-47K-RC Desc.: Metal Film Resistors - Through Hole 47Kohms 1% 50PPM
Mouser #: 271-360-RC Desc.: Metal Film Resistors - Through Hole 360ohms 1% 50PPM
Mouser #: 271-36K-RC Desc.: Metal Film Resistors - Through Hole 36Kohms 1% 50PPM
Mouser #: 271-10K-RC Desc.: Metal Film Resistors - Through Hole 10Kohms 1% 50PPM
Mouser #: 279-LR1F4R7 Desc.: Metal Film Resistors - Through Hole 4.7Ohm 3/5W 100PPM (2 of)
Mouser #: 512-UF4004_Q Desc.: Rectifiers 1A 400V (4 of)


Did you ever measure pin 30? I haven't had much time to play around with my 9800 lately.

Lee.
 
Here are the new voltages shown below in green, with the old in red.

pins 1&2: -6.2v, -51.5, should be -52v, regulated
pins 3&4: +4.2v, +51.7, should be +52v, regulated
pins 5&6: -0.3v, +31.8, should be +32v, regulated
pin 7: -0.3v, +18.6, should be +18v, regulated, provides power for display circuit
pin 8: 0v, ground
pin 9: raw, -75.3v, -54.4, unregulated
pins 10&11: -0.2v, -31.5, should be -32v, regulated
pin 12: raw, +74.6v, +52.2, unregulated
pin 13: raw, +74.6v, +71.2, unregulated
pin 14: 0v, ground
pin 15: raw, -75.5v, -72.7, unregulated
pin 16: +6.6vac, +6.4vac
pin 17: +56.6vac, +55.9vac
pin 18: +56.5vac, +55.8vac

Trying to work out why the protection relay wouldn't click in, I measured some more voltages. On the "DC balance" adjustments section of the service manual, it says there should be 60mV between terminal 26 and ground (left channel amp board) and terminal 11 and ground (right channel amp board). I measured -67.6mV and -50.3V, respectively, so something is wrong here.

Lee.
 
Lee; The DC Balance between pin 26 and ground should be ZERO VOLTS +/- 60mv. Read the manual again. Get it as close to zero as you can. Under 20mv is very good. The pots are gonna be touchy so breathing on them would change them.

Once you get that good, then set the idle current per the instructions. If you don't understand it, don't change it, ask questions 1st.

Larry
 
Lee; The DC Balance between pin 26 and ground should be ZERO VOLTS +/- 60mv. Read the manual again. Get it as close to zero as you can. Under 20mv is very good. The pots are gonna be touchy so breathing on them would change them.

I know. I looked at that page in the manual to see what the DC balance should be. Read my post again. One is way too high.

Once you get that good, then set the idle current per the instructions. If you don't understand it, don't change it, ask questions 1st.

Do I detect an attitude here? I am asking questions, but I also know my way around electronics.

Lee.
 
Yeah Lee. As stated... Those are the DC Balance, which should be Zero. With the one side at -67.6mv, and -50.3v... that can keep the amp in protection. Turn the Idle Current pots (VR 3,5,4,6) fully counter-clockwise, then the VR1 & VR2 to as close to center as you can "eyeball." Then power it on and set the VR1 & VR2 to attain as close to Zero mv as you can. Let it warm up for at least 20 minutes if possible. Not so critical on the DC Offset (Balance), but very important for the Idle Current adjustments. If you still have the original pots in there, this will be tricky, as they are hyper-sensistive. SIDE-NOTE: The Bourns replacements are really nice in that they are much less sensitive and can be dialed in easier.
 
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I know. I looked at that page in the manual to see what the DC balance should be. Read my post again. One is way too high.



Do I detect an attitude here? I am asking questions, but I also know my way around electronics.

Lee.

No attitude. I don't know your level of expertise is all, so I tend to the novice side to be safe. Sorry if I offended.

The way you wrote the DC Balance sentence, it reads that between pin 26 and ground it should be 60mv. Which is not what the manual says. It says 0 with a variance of plus or minus 60mv. That gives you a spread of 120mv and the one side is just over 10% out of spec. Doesn't matter whether it's minus or positive voltage. But the closer to zero you get on the DC Balance the better. Like I said previously and Solutionroom backed up, the pots are very twitchy. So you'll get large swings with just touching them.

Larry


ADD ON: Lee, I went back and read that sentence for the 11th time. 50 VOLTS????? No wonder you got hot under the collar. I do Apologize. I don't know how I missed the lack of "milli". I'm sorry, man. You definately got something wrong. I'd start by pulling the outputs on that side, and testing them. A power up might be something to look at while that side's outputs are out if it's safe to do so on this amp. Some are, some aren't. If not you're limited to testing the outputs by DMM.
With it being Minus(-)50V check Q8-Q10(Outputs) & Q36(driver) and the .47R emitter resistor(R-82) on the negative rail.
Larry
 
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Yeah Lee. As stated... Those are the DC Balance, which should be Zero. With the one side at -67.6mv, that can keep the amp in protection. Turn the Idle Current pots (VR 3,5,4,6) fully counter-clockwise, then the VR1 & VR2 to as close to center as you can "eyeball." Then power it on and set the VR1 & VR2 to attain as close to Zero mv as you can. Let it warm up for at least 20 minutes if possible. Not so critical on the DC Offset (Balance), but very important for the Idle Current adjustments. If you still have the original pots in there, this will be tricky, as they are hyper-sensistive. SIDE-NOTE: The Bourns replacements are really nice in that they are much less sensitive and can be dialed in easier.

Can you be more specific on those replacements.
What is the part number in case I (others) want to swap em out later.

I noticed when I was adjusting mine how sensitive the originals are like you state. Thanks.
 
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