Pioneer SA-9800 fell down from waist height during shipping...

[ondaride]

Hi My story isn't short, but I'll try to be.
The amp was dropped accidentally from near-waist height flat onto the top down.
After the drop, the relay started to be noisy and amp started AC outlet hum audible significantly via speakers and headphones.

I ruled out amp/preamp by connecting it separately as preamp or amp only and the hum was in both cases.

Next I open the amp bottom and wood case out and hook it up to my ipad, earspeakers and speakers. I also cut zip-lock from relay tied up to the AWM163 protection board.

I started wiggling and wobbling boards at random one after another while listening to that miserable loud hum. Upon closer looking, I found that AWM163 board has been secured with zip tie and looks slightly bent. I cut that zip lock and felt that hum decreased by many decibels, but still audible. I believe that I have to replace caps on this board and there are three and probably transistor(s). That is to say that zip tie was used by 'techie' in order to cease hum instead of working on this board that is somewhat not to easy to access to remove... even after removing it tied up to wires on pins that are not easy to get around. So I guess my endeavor is to do things right at this moment regardless. The fact that the amp started substantially louder hum I guess was due to the initial faults of joints and possibly active and passive components as well.

I'm not big fan of replacing components and I may probably try to go over solder joints prior removing this board. Thoughts?

 

[The Fuxtor]

boards may have cracked......

 

[ondaride]

So far I can't see cracks on mounted board. Prior usage of zip-tie partially rules-out possibility as well.

 

[The Fuxtor]

maybe check for loosened grounds?

 

[ondaride]

loosened grounds or other stuff was found on protection board already.

 

[The Fuxtor]

did the unit hum before it was dropped? I dont believe caps or transistors would fail from being dropped, but i suppose it couldnt hurt to reflow the boards? You may come across more faults while you are at it.

 

[ondaride]

I resoldered protection board and still when I wiggle, the relay is noisy. Would need to try to remove the board and reattach after cleaning.

 

[The Fuxtor]

I would get a chopstick and apply pressure on different areas of all the boards, if you have hairline cracks, they should be revealed . I am not sure what you mean by " noisy relay" ? In my experience , if a relay is not soldered proper or has cold solder joints it will either become intermittent with one or both channels. , or will turn on and off making lots of clicking noise....

 

[NAD80]

Check all the solder joints. Check using good lighting and a magnifier. Reflow where needed. The Fuxtor is correct on checking on the possible damage to the boards. ondaride Welcome to AK. Pics would help since I have no idea what the inside of the 9800 looks like.

 

[ph2113]

If you suspect the AWM163 board to be the cause of the noise and hum then you can make a test, bypass it by connecting power output directly to earphone socket(you must disconnect the earphone socket from AWM163 board),by listening to the earphone you will find out the result in just few seconds.hope it helps.

 

[ondaride]

ph2113, brilliant. i'll keep posted. buzzing in the sense of insecure contact and it's sealed relay you can't open and clean.

 

[SaturationPt]

Is it both channels? I / we are assuming that you're talking about a hum from the speakers/outputs, not from the amp itself.

If both channels, it is either a ground or power supply. Disconnect the preamp from the amp (using the switch on the side), does it still hum? If so, you've likely eliminated the preamp. If not, then definitely the preamp.

Do you have a scope to look at waveforms through the circuits?

 

[ondaride]

Please note my first post. I did amp-preamp connect-disconnect to rule out prior asking.

 

[ondaride]

I have scope meter and signal generator.

 

[ph2113]

The cover of the relay could be pried open(look for the small holes on both sides,close to bottom),after that you can clean the contacts,

ph2113, brilliant. i'll keep posted. buzzing in the sense of insecure contact and it's sealed relay you can't open and clean.

 

[Tom B]

boards may have cracked......

When units are dropped like this, I agree that cracked ckt board, or damaged foil trace connection is a likely cause. Logical places to look are boards that have a heavy component on them (Power supply boards with large capacitors, or regulator transistors with heatsinks). Driver boards with driver transistors with heatsinks are other places. Common places for breaks are where the screw holds the board down if this unit uses that method of securing. Many time those points are also used as a ground leg, so a crack there may cause hum. Other places to look are where components are connected to a board, and then secured to the chassis, like all your controls and switches. Cracks and foil connection breaks can happen where the volume control, tone control, balance control, or switches connect to the circuit board. Breaks and cracks, and bad solder connections can also occur on tuner boards near the tuning cap, but this unit wouldn't have that as its an SA integrated receiver.

 

[SaturationPt]

I have scope meter and signal generator.

Okay good.

As you have buzzing from the relay (are there two like the 9900 or only one?) I suspect power supply. Might be related to the drop, might not. Scope the DC outs on your power supply to see if there is AC or unacceptable ripple. Too much ripple can affect the driver for the relay also.

There is no point IMO to cleaning the relay contacts, if it's buzzing it's the DC to the relay, not the contacts. Also, the contacts will not respond well to "cleaning", will quickly become a problem again as the original coating on the contacts is gone (cheap part, I almost always replace them, did in my 9900 and 9800).

 

[BilboBaggins]

The other thing, in case you haven't done this yet, is to reseat all the connectors. A jar like that could loosen something, although marginal component failure is more likely in my opinion. Cracked resistors, anything that is breakable. Good luck!

 

[SaturationPt]

I don't remember any connectors on the 9800, I believe that they are all wire-wrap.

 

[ondaride]

Hi all and THANKS!
I'm back to my wounded baby and will try to bring it back this weekend singing without 'sore throat'
Hi 9800 has wire-wrap connectors -- pain in arz fo sho! I will have to solder out them and keep wire on and than put everything back. Will start from disconnecting a control board, but first, Should I use VARIAC or I'm pretty much safe at this point? I'll use the diagram to bypass control board and post probably few pictures!
I was able to remove relay from chassis -- took quite a time to remove accurately, but sprayed and cleaned with soft no-fuzz cotton cloth.
If the rest of circuit functional, than control board will face overhaul.