700M made a sizzle noise....POP....won't power up.

[davstev]

I hope someone can help. I recently purchased a 700M and I have been loving it.

Today, I was listening, and, then blew the fuse at the back. Unit won't power up.

I then went and got new fuses, and replaced it.

Upon attempted power up- a sizzle sound, and a not too loud 'pop', and that electric burning smell, fairly strong.

The new fuse did not blow. Nothing's working. I have the lid off, looking for blown caps.

Any ideas? That sizzle worries me.

Input appreciated, before I get into this thing.

Thanks.

 

[EchoWars]

By replacing the fuse, you have now smoked the soft-start resistor. Any time a big-azz fuse, like the 12A in a 700M pops, it isn't an accident. Something serious has occurred and needs attention before you try to power it back on. By replacing the fuse without investigating the cause of the failure, you have complicated the repair. Not by a lot, but replacing that resistor is a bit of a PITA.

You almost certainly have some blown outputs, and for sure a blown soft-start resistor. Once these issues are addressed, the unit needs to be connected to a current-limited supply when powered up next. A homemade DBT would do the job well here.

 

[davstev]

By replacing the fuse, you have now smoked the soft-start resistor. Any time a big-azz fuse, like the 12A in a 700M pops, it isn't an accident. Something serious has occurred and needs attention before you try to power it back on. By replacing the fuse without investigating the cause of the failure, you have complicated the repair. Not by a lot, but replacing that resistor is a bit of a PITA.

You almost certainly have some blown outputs, and for sure a blown soft-start resistor. Once these issues are addressed, the unit needs to be connected to a current-limited supply when powered up next. A homemade DBT would do the job well here.

Thanks for this. I am reasonably adept at electronics, a wizard by no means. Should I start with the schematic, and take it from there? locate it, Replace the soft-start resistor, and then replace the outputs? The outputs, btw, you mean what exactly?

Thanks, EW.

 

[petehall347]

output devices ..ie transistors on big heatsink ..the big ones that supply power to the speakers ...might be more things blown too like the drivers for the outputs and associated resistors . it all needs checking .
its most likely its just one channel let go ..either left or right ..determine first which side is bad first .. test the outputs for short circuit first ... most times they go short from emitter to collector .

 

[EchoWars]

SS resistor is mounted inside the back panel. I've been replacing them with a 4 ohm 25W aluminum chassis-mount job. There's a slew of wires that connect to it, and the itty-bitty azz holes in the resistor leads are too small to accommodate them all. I have a tiny tiny diamond burr tool that I use to elongate the hole so I can tuck all the wires into it.

Like I said, replacing that resistor sucks.

 

[davstev]

SS resistor is mounted inside the back panel. I've been replacing them with a 4 ohm 25W aluminum chassis-mount job. There's a slew of wires that connect to it, and the itty-bitty azz holes in the resistor leads are too small to accommodate them all. I have a tiny tiny diamond burr tool that I use to elongate the hole so I can tuck all the wires into it.

Like I said, replacing that resistor sucks.

Ok, thanks. Seems my amp and I will be in a whole new "getting to know each other" phase.

Where best to get a pdf of the service manual for the 700M?

I looked on Stereomanuals.com, but nothing was evident. Nothing on hifiengine.com either.

Thanks.

 

[bmwh548]

Elektrotanya. There's two schematics there, hope they're the right ones:

http://elektrotanya.com/kenwood_700m_power_amplifier_sch.zip/download.html

http://elektrotanya.com/kenwood_700m_pwramp_sch.pdf/download.html

 

[davstev]

Elektrotanya. There's two schematics there, hope they're the right ones:

http://elektrotanya.com/kenwood_700m_power_amplifier_sch.zip/download.html

http://elektrotanya.com/kenwood_700m_pwramp_sch.pdf/download.html

Thank you for this, sincerely. However, that ElektroTanya.com is the most confusing website I have ever used.

I have no idea how to actually download, or for that matter, to be able to sign up and then download.

Will continue to investigate.

 

[davstev]

Yup, as seen in the attached photo, a blown soft start resistor. The right hand side is blown out, you can clearly see it.

So, with some difficulty, I will replace this, making sure all the connections to it are maintained and soldered in properly.

I know that this is not "the repair" in it's entirety, only a starting point for further investigation. I WON'T try to power up once it is replaced.

Turn thereafter to the outputs?

 

[davstev]

SS resistor is mounted inside the back panel. I've been replacing them with a 4 ohm 25W aluminum chassis-mount job. There's a slew of wires that connect to it, and the itty-bitty azz holes in the resistor leads are too small to accommodate them all. I have a tiny tiny diamond burr tool that I use to elongate the hole so I can tuck all the wires into it.

Like I said, replacing that resistor sucks.

This is gonna suck! :yes:

So many wires!

 

[CohibaJoe]

I have been there....This is your Best Friend: Dim Bulb Tester
http://www.audiokarma.org/forums/showthread.php?t=465423

Once a fuse pop's I do not replace as more damage can occur...that's when I would use the DBT then fuse to test.

Good Luck....

 

[DrumminDaddy]

EW's sticky is awesome!

http://www.audiokarma.org/forums/showthread.php?t=43186

Good luck with your amp. :thmbsp:

 

[Alienz]

Thank you for this, sincerely. However, that ElektroTanya.com is the most confusing website I have ever used.

I have no idea how to actually download, or for that matter, to be able to sign up and then download.

Will continue to investigate.

It is a bit confusing but he has some schematics etc which I couldnt find anywhere else. Sign up is not needed.

It takes a few minutes or so for the download link to become active, right under document preview it says 'processing', wait a little while and the link will become active, hope this helps.

 

[EchoWars]

700M Manual @ Stereomanuals.com: http://www.stereomanuals.com/man/rep/kenwood/kenwood_manuals_0_xx.htm

If you're serious about tackling this, you need a good printed manual.

 

[davstev]

It is a bit confusing but he has some schematics etc which I couldnt find anywhere else. Sign up is not needed.

It takes a few minutes or so for the download link to become active, right under document preview it says 'processing', wait a little while and the link will become active, hope this helps.

Hey, Alienz, I really appreciate your comment! I will give it a go.

 

[davstev]

700M Manual @ Stereomanuacom: http://www.stereomanuals.com/man/rep/kenwood/kenwood_manuals_0_xx.htm

If you're serious about tackling this, you need a good printed manual.

Very serious. I've already located some blown output transistors.

Thanks for the tip on the manual.

 

[EchoWars]

Hopefully, you found this thread as well: http://www.audiokarma.org/forums/showthread.php?t=222069

Some good info there, as well as some scats that won't be in any manual (I did re-draw the main-amp section to make its workings clearer to me back in the day...there's a pdf of it in that thread).

 

[davstev]

Greatly appreciated, EchoWars.

Since I am getting into the guts of the 700M anyway, I am wondering if I should recap this 40 year old. At least on the driver boards, which seem fairly accessible.

Would the huge filter caps benefit greatly from replacement?

Addendum: I just noted that there are lots of threads here that answer this question.

 

[davstev]

It is a bit confusing but he has some schematics etc which I couldnt find anywhere else. Sign up is not needed.

It takes a few minutes or so for the download link to become active, right under document preview it says 'processing', wait a little while and the link will become active, hope this helps.

I got to the schematics, but they are the same ones as on hifiengine.com.

I think the full 'service manual' is more useful to me; according to EchoWars, I can get one at StereoManuals.com (for a price); it seems to be about 35 pages, so a different, and probably better, document. Just FYI.

Thanks.

 

[davstev]

By replacing the fuse, you have now smoked the soft-start resistor. Any time a big-azz fuse, like the 12A in a 700M pops, it isn't an accident. Something serious has occurred and needs attention before you try to power it back on. By replacing the fuse without investigating the cause of the failure, you have complicated the repair. Not by a lot, but replacing that resistor is a bit of a PITA.

You almost certainly have some blown outputs, and for sure a blown soft-start resistor. Once these issues are addressed, the unit needs to be connected to a current-limited supply when powered up next. A homemade DBT would do the job well here.

Thinking more about the "something serious has occurred" that you mention above... what happened was, that I have a phono preamp, which I was powering off, while the volume on the 700M was pretty high (too high). I've stupidly done this before- forgotten to turn the volume down before powering off the phono pre. It makes a loud 'pop' through the speakers with the 700M volume up but usually no harm done, But, this time, I looked over at my 700M and it was dead due to the blown fuse. Maybe some damage occurred at this time. But the REAL damage happened when I replaced the fuse, turned it on, and fried the amp...:thumbsdn: