Yamaha YST-SW216 Subwoofer

[Chevy2]

Got two of these (both defective) for $5. Was troubleshooting and I'm stumped. For the one that outputs sound, it has some bass, but is extremely scratchy. Here are the voltages and service manuals if anyone can give me any tips on what to check next. I have pictures of the boards, but all the components on both look perfect, but let me know and I'll upload.

Voltage on the STK404
1 .2
2. .2
3. 0
4. -33.6
5. 13.8
6. .44
7. 1.74
8. -33.9
9. 33.7
10. 0

[madan1]

Re: Yamaha YST-SW216 Subwoofer

Yes, upload the pics.
Are the drivers ok?

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

Here are the pics of the two boards. Out of the two, this is the only one that will output audio (on both the relay clicks on). I was thinking of switching the input board to see if that made any difference on this one, but didn't want to risk breaking anything else.

The driver sounds fine.

[budm]

Re: Yamaha YST-SW216 Subwoofer

https://www.badcaps.net/forum/attach...4&d=1492889220
So do you have +15VDC, -15VDC on the connector that goes to the input board?

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

https://www.badcaps.net/forum/attach...4&d=1492889220
So do you have +15VDC, -15VDC on the connector that goes to the input board?

Yes, I have +13.9 and -13.9, if that is close enough.

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

I switched the audio boards between the two to see if that made any difference. It sounded exactly the same.

[madan1]

Re: Yamaha YST-SW216 Subwoofer

Can you record and upload the sound it produces?

By the way, what's your idea - to have two working units or to scrap parts from one of the units to fix the other one?
Also, to be able to follow what's going on here, can you summarize like:

unit 1
known faults -
measured V -
checked components -
and so on

unit 2
....
...
...


The +/- 15V on the connector power up some op-amps and for this purpose the voltages are within the limits.. still, I think they are low.. indeed all voltages are low

[budm]

Re: Yamaha YST-SW216 Subwoofer

If you touch either end of resistor R66 with your finger, you should hear 60 cycle hum coming through the speaker.
Also look really close on the solder pads of the STK to make sure it does not have cold joints with crack ring around the solder joints.

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

Can you record and upload the sound it produces?

By the way, what's your idea - to have two working units or to scrap parts from one of the units to fix the other one?
Also, to be able to follow what's going on here, can you summarize like:

unit 1
known faults -
measured V -
checked components -
and so on

unit 2

I'd like to eventually get both working, but I'm not against taking parts from one to get the other working. I've used the schematic to check voltages, but everything seems good enough, to where I thought Id post here for guidance on what to systematically check. The voltage on units 2's STK 404 make it look like it's fried?

Voltage on the unit 2's STK404
1 .15
2. .15
3. 0
4. -31.5
5. 13.8
6. 17.2
7. 14.5
8. -32.1
9. 32.3
10. 0

and I'll try to get some audio.

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

If you touch either end of resistor R66 with your finger, you should hear 60 cycle hum coming through the speaker.
Also look really close on the solder pads of the STK to make sure it does not have cold joints with crack ring around the solder joints.

I do get a hum if I touch that resistor and i thought about touching up the soldering. Will try that this weekend.

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

Would it hurt anything to pull the 404 and measure the voltage with it out of the circuit?

[Chevy2]

Re: Yamaha YST-SW216 Subwoofer

Turns out both had a bad STK404. Replaced them in both and now both are working. Thanks everyone for the help.

[21balu]

Re: Yamaha YST-SW216 Subwoofer

Hi can you tell me yamaha YST SW216 power transformer output because my subwoofer transformer output not showing.

[budm]

Re: Yamaha YST-SW216 Subwoofer

Hi can you tell me yamaha YST SW216 power transformer output because my subwoofer transformer output not showing.

If you look at the service manual, it shows 53.3VAC center tab, the current rating may be around 1.5 ~ 2A.
Are the fuse and the power switch in the hot side OK?

[Long Peter]

Chevy2 Can you (or anyone else) please advise a reliable source for the STK404-070? My brother has a YST SW216 wherein the transistor is generating a lot of heat and not making any sound. All our Google-fu is turning up a reproduction parts of dubious origin/quality. The more reputable vendors seem to be out of stock or not show a listing at all any more. Also can't work out what the N-E and YN-E suffixes means.