[baronbeehive]

The side of the 2k resistor nearest the pot only is grounded

 

[baronbeehive]

Yes if you want to skype now fine.

 

[klnglim]

Right!

Glad you went back to stock 150 ohm power resistors!

What coupling caps did you use? I'm guessing they were in before you got the amp?
Did you solder from the other side of the board? It looks like it, that's good.

If someone modded the amp before you got it that could cause a problem as removal of the board can cause wires to break. Also your cathode caps should not have burnt!

I bought this amp brand new from Taobao.com 6 months ago, since used from first day, the amp is quite hot and that's why I install 2 DIY PC blue LED quiet fan under the case.
Past few weeks suddenly smoke and bad smell burnt came out from inside the amp, noticeable one from the four power tube was too bright, I unplug electric cable away from the amp ASAP
When the amp cooling down I opened the bottom case, some leaking melt liquid spread over some parts of the board from original Philips blue capacitors & 2 resistors burnt black are clearly seen.
During that time I suspected transformer may be provided over current but the fuse looked normal, so I ordered some resistors and capacitors for replacement. I took out the whole board solder both side which apply. The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.
Now those replacement seen from picture is just for temporary, as I plan to upgrade better quality parts soon. Please feel free to give any adavise or recommendation for further improvement?

Already more than hour the amp operate now, so far no burnt, no bad smell, meter show stable (left is 50mA & right is 60mA), heat temperature whole case isn't very hot but I have seen very little smoke out from inside.
Is this look normal?

 

[baronbeehive]

I bought this amp brand new from Taobao.com 6 months ago, since used from first day, the amp is quite hot and that's why I install 2 DIY PC blue LED quiet fan under the case.
Past few weeks suddenly smoke and bad smell burnt came out from inside the amp, noticeable one from the four power tube was too bright, I unplug electric cable away from the amp ASAP
When the amp cooling down I opened the bottom case, some leaking melt liquid spread over some parts of the board from original Philips blue capacitors & 2 resistors burnt black are clearly seen.
During that time I suspected transformer may be provided over current but the fuse looked normal, so I ordered some resistors and capacitors for replacement. I took out the whole board solder both side which apply. The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.
Now those replacement seen from picture is just for temporary, as I plan to upgrade better quality parts soon. Please feel free to give any adavise or recommendation for further improvement?

Already more than hour the amp operate now, so far no burnt, no bad smell, meter show stable (left is 50mA & right is 60mA), heat temperature whole case isn't very hot but I have seen very little smoke out from inside.
Is this look normal?

Oh I see you got it from new therefore the problems was before you modded it. I hadn't seen those coupling caps before. Unlikely to be a faulty cathode cap to cause them to burn out, and not an overheating problem with the MKViii. Which resistors were burnt?

 

[Maxx134]

This resistor is on the previously faulty circuit I'm sure because it is close to the problem solder joint that I had to repair, when one leg of the WCF cap became disconnected from the trace

I bet that resistor once taken out (carefully) would read proper resistance .
If it not not b burnt it most likely good.

I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..

I bet there is an error in connection by your socket

 

[klnglim]

Oh I see you got it from new therefore the problems was before you modded it. I hadn't seen those coupling caps before. Unlikely to be a faulty cathode cap to cause them to burn out, and not an overheating problem with the MKViii. Which resistors were burnt?

The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too

 

[baronbeehive]

The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too

Were they the 150 ohm power resistors?

If you swap around the tubes you may find a faulty tube causing the different meter readings.

I bet that resistor once taken out (carefully) would read proper resistance .
If it not not b burnt it most likely good.

I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..

I bet there is an error in connection by your socket

Right I'll have a closer look. So difficult to see properly under all these mods!

 

[klnglim]

Were they the 150 ohm power resistors?

If you swap around the tubes you may find a faulty tube causing the different meter readings.



Right I'll have a closer look. So difficult to see properly under all these mods!

The power tube is brand new like original, all light up normal.
The resistors are new 150R 5Watts
Vishay AC05 Series Axial Wirewound Resistor 150Ω ±5% 5W -80 → -10ppm/°C

Now The sound is great, clear details, wide sound stage, bass improvement is most noticeable

 

[baronbeehive]

The power tube is brand new like original, all light up normal.
The resistors are new 150R 5Watts
Vishay AC05 Series Axial Wirewound Resistor

Now The sound is great, clear details, wide sound stage, bass improvement is most noticeable

Those resistors did have a nasty habit of burning, lets hope now that you've put in better ones the problem will stop.

Fan cooling alone might not have been enough with those crap resistors, but now that you've installed fans to keep it cool that should be fine.

 

[Maxx134]

Honestly, I like the design of the amp but very disappointed with some **** components inside the board

Don't be because ALL commercial amps have such problems of cutting costs and using cheapo parts.
The fact remains that this amp has a great balanced design and Luke any amp needs work to elevate it.

I turned on the amp again after few hours rest, now it runs very stable and lower temperature without smoke or bad smell

Then don't worry.
It was probably your PSU resistors they always slow burn to a higher amount and balance out.

You must keep each over any power tube glowing brighter which means a tube going bad.

There's something funny going on there, try to look to see if you can see which resistor is burning, those by the PSU look off,

Yeah he could have had thermal runaway on one tube which caused that cap failure.
I assume new parts keeping all in check.

The Rifa bypasses on the coupling cap are not recommended in this area,

It didn't matter and those caps he had are better then the French caps that are there...

It should be noted that MANY amps are using these same cheapo French caps,
because they are cheap and look fancy..

Still. the RIFA he had on top are better.

I have just cut off Rita bypass from coupling cap

You could have left them on for a lower frequency response cut off, so deeper bass..

Don't replace or order anything. Replacing parts blindly is a good way to waste money and burn more parts

Exactly... Coin is right.

Surely going from 106k to 1.9k means it has gone open, ie. less resistance?

Your terminology is off:

Open=high resistance = burnt

Short= Low or zero resistance= closed

The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.

That is the nice looking cap which is supposed to be a good buy for manufacturers..
You will notice big improvement upgrading here..

Is this look normal?

Yes

The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too

The new wirewound resistors can withstand more power and would give of a bit smoke if tube was faulty.
Keep an eye on the meters of one goes higher.
Otherwise don't worry

 

[klnglim]

Those resistors did have a nasty habit of burning, lets hope now that you've put in better ones the problem will stop.

Fan cooling alone might not have been enough with those crap resistors, but now that you've installed fans to keep it cool that should be fine.

Can u give me the website where to order those caps and resistors for upgrade?
I m from Sydney, Australia by the way

 

[baronbeehive]

Sorry in Europe we mostly use hificollective.co.uk I don't know anywhere in Australia, but if you want to know exactly what to order we can help when you decide exactly what you need.

 

[Maxx134]

Can u give me the website where to order those caps and resistors for upgrade?
I m from Sydney, Australia by the way

For you better to look for local parts seller you probably can find on Google a parts company

 

[klnglim]

Sorry in Europe we mostly use hificollective.co.uk I don't know anywhere in Australia, but if you want to know exactly what to order we can help when you decide exactly what you need.

I plan to ugrade PSU caps to MUNDOLF brand
4 x coupling with K75-10
8xMills MRA5 150R/5W resistors
A lot of cables I have own so cable upgrade is skip
After some times self learn and pratice, soldering isn't any issue anymore.
Since last mod experience, take off the whole board out from the amp is not hard at all
Myself already own some drivers tubes & NOS, so skip tube row

 

[baronbeehive]

I plan to ugrade PSU caps to MUNDOLF brand
4 x coupling with K75-10
8xMills MRA5 150R/5W resistors
A lot of cables I have own so cable upgrade is skip
After some times self learn and pratice, soldering isn't any issue anymore.
Since last mod experience, take off the whole board out from the amp is not hard at all
Myself already own some drivers tubes & NOS, so skip tube row

Sounds good, those are important upgrades, you already have upgraded cathode caps so good luck!