Sophisticated sabotage on an SA-9800

jcnash

BUSTED!!
Hi Mark and other AK gurus,

I recently picked up an SA-9800 locally for pretty cheap. Tested it before buying and it plays music but with the usual scratchy pots, etc.

However on closer examination after bringing it home, I found that the music is not as "clear" as is normal for the 9800. Also a few other issues caught my attention:

1. When the unit is powered on, fluoroscan meter / pilot turn on as normal.
2. Music starts playing immediately (literally as soon as i flick the power switch on!)
3. HOWEVER, there is no protection relay click!

Upon opening up and taking a look, I found several signs of non-factory soldering, use of very cheap quality (single thin strand) wire, etc.

While the amp does play music, Im concerned that the previous repair job might have included bypassing the protection relay circuitry which is needless to say, putting the amp at risk overtime I use it.

Any advice on where I should start looking to investigate this issue?

Thanks in advance.
 
Well get the service manual/read-up and start to go over the wiring pcb's etc to figure out what was done to the unit. Obvious places are the wire mods to figure out where they are attached too and figure out what's going on with the protection relay circuitry. Some pics will help identify what's going on too. Pioneer used solid wire, not sure if this is factory or mods.
 
It's a NSA circuit - look for transistors in the amp that unsoldered themselves, or cracked their joints.

Refresh the power supply. eagle eye the protection circuit.
 
Thanks Mark & rcs16.

Took a look at the protection board today, and turns out *surprise surprise* THERE IS NO PROTECTION RELAY!

Someone has attached jumper cables in place of the relay! Unbelievable!

So next question: Where can I source an ASR-047 relay? If unobtanium, can I get a suitable replacement?

In addition, while playing music, there are a ton of pops and crackles through the speaker, and a pretty loud pop as soon as the unit is turned on. Can the lack of a protection relay be the cause for these?
 

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Couldnt find anything on eBay and Mouser. Product discontinued on the Pioneer website.

Am I SOL? Any other sources I should check?
 
The pop you hear on startup is the reason why they have the relay. It can potentially destroy your speakers, so be careful. For the rest, you have to wait until one of the guru's drops by.
 
Couldnt find anything on eBay and Mouser. Product discontinued on the Pioneer website.

Am I SOL? Any other sources I should check?

Should be easy enough to cross the relay to something non-pin compatible and fly wire it. Hell, you could even re-drill the PCB and fit one using jumper wires on the solder side.
 
ASR-047 is the SAME relay as used in the SX-1280 protection circuit.

653-MY2-02-DC48 from mouser, 17 in stock @$11.97 ea
 
Mark,

While waiting for the relay to arrive, I figured id start to troubleshoot some major hum that I hear through the speakers because of this amp.

Ive looked through some other threads with the same problem that you helped troubleshoot and have done some preliminary analysis.

1. Tested hum by connecting/disconnecting pre-power amp jumpers:
Most of the hum seems to come from the pre-amp section. As soon as the jumper is removed, the hum reduces significantly BUT still exists.

2. The tone controls (tone switch, bass/treble knobs) do affect the hum level - further indication that a majority of the hum seems to come from the pre-amp section.

3. Ive tried reversing mains power polarity - no affect.

4. This amp also has another issue where the Fluoroscan meter lights dont come on EVERYTIME the power switch is turned on. For example: I could flick the power switch on and the pilot lamp will turn on, but the fluoroscan meters will not light up. I would need to turn the power switch on and off 4-5 times and finally, if Im lucky, the fluoroscan meter will light up as well.

5. There is no audio when the amp is ON but the Fluoroscan meter lights are NOT (even with correct source selected, speakers connected, etc). Audio works fine with the Fluoroscan meter is lit up.

6. There is no HUM when the amp is ON but the Fluoroscan meter lights are NOT (even with correct source selected, speakers connected, etc). HUM exists only when the Fluoroscan meter is lit up.

7. The level (volume) of the hum varies. Ex: When the amp is turned out after being powered off overnight, the hum volume might start off being low OR high. As the amp sits powered up, the hum usually gets louder and louder with sudden dips and spikes in hum volume.

I really have no idea what to make of this! Worn capacitors? Other issues? Would really appreciate your thoughts!

Absolutely no rush on this as Im waiting for the relay to arrive anyway.

Thanks Mark!

jcnash.
 
That's also my idea, see what voltage comes out of the power supply. Maybe it is also the origin of the hum issue.
 
First thing I would check is the DC offset. If it is bad enough to cause a hum you are cooking the voice coils in the woofers.

I'll bet you are going to find the new relay does not kick in, why else would someone jump it ? If there is no offset then there is a fault in the protection circuit itself. If there is offset do not run it on speakers until that is corrected.

I know jumping out the relay is the work of a quack, but there had to be a reason. nobody would have touched it if it worked.

I believe one of the sources for the amp itself is common to the one of the sources for the flouroscans, that will probably turn out to be a bad connection in the power supply. Test all the voltages whne it is not working. In fact you could try beating it with the handle of a screwdriver or sometning. If it comes on then you know. At that point you might just find it by visual inspection.
 
Don't be beating the boards up.

make these voltage measurements, copy and add your results to the end of each line:

awr-191/194 power supply
awr-191/194 pin 3 +52v DC regulated
awr-191/194 pin 5 +32v DC regulated
awr-191/194 pin 7 +18v DC regulated
awr-191/194 pin 11 -32v DC regulated
awr-191/194 pin 1 -52v DC regulated
awr-191/194 pin 8 +48v?? DC UNregulated

awm-163 protection board
awm-163 pin 12 0.000v DC left channel output
awm-163 pin 13 0.000v DC right channel output

I see some things that could happen, depending, but not certain enough to voice them - let the voltage readings tell the tale.

And yes, I expect to direct a full power supply rebuild. Transistors (hopefully q6 and q7 are ok), caps, diodes...
 
Thanks all for your comments.

Mark, attached are the voltage readings you requested. The first column of readings are with the unit powered up but with the Fluoroscan meter off (malfunctioning mode). The second column of readings are after the 10+ power on/off cycles, when the meter ultimately lit up. i.e....
Pin : Reading with meter OFF : Reading with meter ON

awr-191/194 power supply
awr-191/194 pin 3 +52v DC regulated : +5.3v : +52.8v
awr-191/194 pin 5 +32v DC regulated : -0.3v : +32.3v
awr-191/194 pin 7 +18v DC regulated : -0.3v : +19.3v
awr-191/194 pin 11 -32v DC regulated : -1.1v : -32.2v
awr-191/194 pin 1 -52v DC regulated : -9.2v : -55.0v
awr-191/194 pin 8 +48v?? DC Unregulated : 0v : 0v (not sure what implications this voltage being unregulated would have(?). This reading is with the DMM set to a normal DC voltage setting. Should it be measured using a different procedure?)

awm-163 protection board
awm-163 pin 12 0.000v DC left channel output : -0.113v (fluctuating): -0.035v (fluctuating)
awm-163 pin 13 0.000v DC right channel output : -0.120v (fluctuating) : -0.025v (fluctuating)

All the power supply pins seem to have different voltages when the meter is on vs. off. This makes sense as the meter board isn't seeing the necessary voltages as inputs to power up. That is however, as far as my limited circuit knowledge will take me, as identifying the source of the intermittent missing voltages on the power supply board is beyond my level of expertise. :)

Thanks very much Mark!
 
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EVERYTHING keys off the +52v regulator, and it's zener reference voltage... If it goes, everything goes.

There is either an external intermittent on the board, or a component has a glitch. D5 (6.0v zener) rules them all.

Can't say it enough, REBUILD the power supply and things will settle down.
 
Post a pic of the output transistors array- have they been messed with?

Anyone who bypasses a relay is likely to have bodged an output transistor replacement too.
 
EVERYTHING keys off the +52v regulator, and it's zener reference voltage... If it goes, everything goes.

There is either an external intermittent on the board, or a component has a glitch. D5 (6.0v zener) rules them all.

Can't say it enough, REBUILD the power supply and things will settle down.

Thanks Mark. Looks like the only way to resolve this permanently is to rebuild the power supply completely. Ive been trying to avoid it because Im just unsure if my skills are sufficient to finish this successfully. Is ti a fairly intense procedure? As you know, Im able to measure voltages, etc. and am good with a soldering iron. What are your thoughts?

Also, is the hum through the speakers potentially created by the power supply components as well (ie...will a power supply board rebuild fix the hum issue as well)? Thoughts?

In addition, while I'm at it, should I also replace the filter caps? The current filter caps are the originals that came with the amp in 1978-80.
 
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Post a pic of the output transistors array- have they been messed with?

Anyone who bypasses a relay is likely to have bodged an output transistor replacement too.

Will do John. Im not really sure what the output transistors look like, but I will look around in the unit and post a picture.
 
Rebuilding the power supply is fairly easy but you have to pay close attention to the pinout of the transistors. If you rebuild it, have a look in the HG service manual. You will see two extra transistors. These will help to keep the heat down.
 
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