Should a transformer live/neutral pins have continuity?

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

Yea one side has been cut off

[budm]

Re: Should a transformer live/neutral pins have continuity?

Lots of bad solder joints with crack ring on the solder around the components'legs.

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

That is pretty shocking soldering, whwere do you see the ring fracture?

[budm]

Re: Should a transformer live/neutral pins have continuity?

That is pretty shocking soldering, whwere do you see the ring fracture?

If you look at STK-XXX IC legs, you will probably see some there too.
When I work on these I always look through all the boards and redo the joints, and make sure all the board mounting screws are tight because the boards are GND to the chassis with mounting screws.

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

measured the two rubycons. One is measuring 48uF and the other 98uF so one deffo dead

Found one joint on the speaker terminals completely removed from pad taking pad with it looks to be either a grounding or just a support pin perhaps.

Not impressed with the assembly of the unit, way too much flex in the board and nothing really secure.

[stj]

Re: Should a transformer live/neutral pins have continuity?

i cant imagine cutting the side off a relay like that just to save a few coins!
some people are too cheap for their own good!

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

Alright changed the capacitors and that relay but still no luck.

Although I am getting some playback through the headphones but is very low volume and crackly.

Also when a speaker is wired in to the unit and I plug in the mains power cable the speakers makes a popping noise. Which is more than it was doing before.

Where should I explore next?

[SteveNielsen]

Re: Should a transformer live/neutral pins have continuity?

I'd start with the power amp finals circuit, check caps, resistors and fuses there.

Audio boards in general aren't made that well in my experience. Crappy solder joints and weak bond between traces and board are pretty common. Too easy to lift pads and traces with a little too much heat. They often aren't laminated and multi-layered like computer boards are so they flex more too.

[momaka]

Re: Should a transformer live/neutral pins have continuity?

Where should I explore next?

Re-solder all of those joints budm pointed to, and possibly any others you find suspect. Generally, that would be all of the larger components or components mounted on a heatsink.

And wow! Who worked on that unit?! Did they by any chance use a hot chisel or something along those lines to solder? Amusingly terrible job at best!

[modemhead]

Re: Should a transformer live/neutral pins have continuity?

Also when a speaker is wired in to the unit and I plug in the mains power cable the speakers makes a popping noise.

For testing, don't use speakers that you care a lot about. Normally a quiet amp will have near zero DC voltage output. A malfunction can cause it to output a significant amount of DC, which can destroy a speaker by heating up the voice coil.

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

Found 5 dead caps so far at the rear of the unit by the terminals

FRONT LEFT
jamicon 1 - 100v4.7uf @ 5.25uf
jamicon 2 - 100v4.7uf @ 5.33uf
nichicon 1 - 50v10uf @ 11.3uf
elna 1 - 50v0.47uf @ 468nf
rubycon 1 - 10v100uf @ 116uf
rubycon 2 - 10v100uf @ 113uf
jamicon 3 - 50v2.2uf @ 2.5uf

MID BOARD

elna 10v47uf @ 30uf
jamicon 10v47uf @ 15.5uf
nichicon 50v4.7uf @ 4.8uh
nichicon 50v4.7uf @ 4.9uf
rubycon 10v100uf @ 96uf

EXPANSION BOARD

not checked yet

REAR
jamicon 4 - 25v330uf @ 281.3nf
jamicon 5 - 16v470uf @ 23nf
rubycon 3 - 10v100uf @ 113uf
rubycon 4 - 10v220uf @ ...nf
rubycon 5 - 50v1uf@ 1uf
rubycon 6 - 50v10uf@ 11uf
jamicon 16v100uf @ 113uf
nichicon 50v47uf @ 53uf
rubycon 50v4.7uf @ 4.9uf

making some headway. Ive tried photographing where everything was and have kept caps separate in sections they were removed from but a bit worried I may misplace them when putting them back in. Does the service manual tell you locations of caps just in case?

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

So in total found a further 5 dead caps (along with 1 earlier), the rest seem ok. I'm using my multimeter which has capacitance tester built in so wont be the most accurate but should be fine to determine if bad or not. 2 in mid board and 3 at rear of board.

jamicon 25v330uf - Panasonic FR Series 330uF 25V - http://uk.farnell.com/webapp/wcs/sto...&storeId=10151
jamicon 16v470uf - Panasonic FR Series 470uF 16V - http://uk.farnell.com/webapp/wcs/sto...&storeId=10151
rubycon 10v220uf - Panasonic FR Series 220uF 10V - http://uk.farnell.com/webapp/wcs/sto...&storeId=10151
elna 10v47uf - RUBYCON ML Series 47uF 10V - http://uk.farnell.com/webapp/wcs/sto...&storeId=10151
jamicon 10v47uf - RUBYCON ML Series 47uF 10V - http://uk.farnell.com/webapp/wcs/sto...&storeId=10151

Are these replacements ok, chose Panasonic FR where I could but they didn't have much selection for the 10v47uf so had to choose rubycon ML Series. Will these do?

[SteveNielsen]

Re: Should a transformer live/neutral pins have continuity?

Usually general purpose caps are used for audio but those should all be fine.

When changing multiple caps I write down the circuit designation (ex. c1, c2, c3, etc.) which is printed on the board and the value and voltage of each cap as a guide.

[stj]

Re: Should a transformer live/neutral pins have continuity?

use 16v 47uf then

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

They (Farnel) having no FR FC FM in 16v either. They have 1 FC but not in stock

[stj]

Re: Should a transformer live/neutral pins have continuity?

so use 25v

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

Didn't realise you could go that high so is it safe to go as high as you want on V?

Anyhow replacement caps turned up nice and early, wish me luck

[mikay786]

Re: Should a transformer live/neutral pins have continuity?

I give up, still no joy. That's about as much time and money I want to spend on this thing.