problems with X-Can V2

[elysion]

I've changed the tubes in my X-Can V2 a while ago to matched 6N23P-EB's which I've ordered from Mike.

Another pair of these tube type is working PERFECTLY in my X-Can V3 since a few months, but it seems that I have a problem with them in the V2:

– I've changed the tubes in the V2 a couple of weeks ago, but I've used the V2 not much since then.

– My intention was to make some comparisons this weekend and the amp was running from Friday evening until this Saturday evening (somewhat more than 24 hours) to burn-in the tubes a bit. I've checked the sound periodiacally and I listened every few hours for a very short time.

– Saturday evening, I've listened again and what I heard was horrible. It sounded like two broken tubes or a broken amp... but it was not music anymore. The sound was totally distorted. I've expected to find one or two bad tubes or a bad cap or whatever, but as I've opened the amp, I've found NOTHING. Everything looks great. The only soldering joints that look bad are those from the parts that Mike has not changed (original MF parts that MF did solder). All solder joints from Mike look perfect and all new caps look fine (no blown caps).

– I hesitate a bit to change for another pair of tubes, because I'm not sure if something is damaged.

– I guess heat can't be the problem since it was running only somewhat more than 24 hours and the tubes have been working fine in the last 1-2 weeks (but as mentioned I've turned the amp on only for short periods).

– The whole amp seems to have a problem. It's not only on only channel.

– I use a 2000mA linear unregulated wallwart with 12VAC with the V2. The output voltage (without load) of this PSU should be within the save limits that Mike has told me.

I have the amp disassembled at the moment. I can take PICS if needed.

[Deleted]

Christian,

It's unlikely that two tubes have gone at the same time.

Ian

[Deleted]

Christian,

Is there any chance you forgot reattach that pesky flying earth lead to the casing when closing up?

Don't forget to recheck your RCA leads too.

[elysion]

Sept 4, 2011 15:01:19 GMT @cjarchez said:

Christian,

Is there any chance you forgot reattach that pesky flying earth lead to the casing when closing up?

Don't forget to recheck your RCA leads too.

The earth lead was connected properly. I have even scratched the anodizing somewhat to have better contact (I did this long ago).

RCA socket should also be OK, but I will check again.

The strange thing is that I has worked flawlessly for about 20 hours (at least) and then it was shite. That's why I have some fear that it could be a defect.

I guess it's best to reassemble the whole thing, recheck everything and then to try again. After that, I could use the original wallwart to see if the 2000mA 12VAC wallwart is the problem.

At least, everything looks OK. No visible problems noticeable on the PCB.

Thanks for your help. I will report back after testing.

[Crispy]

Is there any chance you forgot reattach that pesky flying earth lead

Christian,

I agree that it could be a simple problem with the earth lead or some earth related problem.

When I was converting my V2 into a pre-amp I had the same problem with a poor soldered earth joint on the Jalco headphone socket, it sounded terrible.
After re-soldering the earth the problem disappeared.

You can guarantee it will NOT be any of the work Mike carried out.

Try checking all earth connections it may? solve your problems.

[elysion]

Finally, I've found the problem. The problem was not the V2 amp. It was the source!

I had a Behringer UCA222 connected to the V2. This one had two modifications. It has a heatsink on the DAC/ADC chip and the case has a (very primitive) shielding. I've tried to shield the case with aluminum spray. Spaying has worked good and both UCA222's that I've modded this way have been working. I guess the problem could be that primitive shielding (because it is not properly grounded). The other UCA222 works perfectly though. Maybe something on the UCA222 PCB got contact to the aluminum layer.

[elysion]

You can guarantee it will NOT be any of the work Mike carried out.

His work is perfect. I've seen the differences between his solder joints and those from the MF factory. The solder joints of MF have not the same quality.

A was a bit suprised about the problem, because I encountered it suddenly. Why did it work a couple of hours ago? I had no clue and perhaps I should have changed the source earlier.

[gommer]

That's electronics for you. It works, but something decays slowly without any noticeable influence and then suddenly it's gone.
This 'something' can be mechanical (wire, sparking, solder joints), semiconductors or even passive components.

Just had this at work. Building a prototype (power electronics) and it woks for hours on end, pushing out 3kW without blinking. Then suddenly... bam, shotgun noise, finished. Turned out to be a very small (SMD) underrated ceramic capacitor that exploded. Took half the board with it by shorting (400V to ground). Don't you just love it

[joethearachnid]

Sept 4, 2011 18:52:20 GMT gommer said:

Then suddenly... bam, shotgun noise, finished. Turned out to be a very small (SMD) underrated ceramic capacitor that exploded. Took half the board with it by shorting (400V to ground). Don't you just love it

Pictures or it didn't happen.

(Incinerated PCB pictures are always fun)

-JoetheArachnid

[PinkFloyd]

Glad it all worked out Christian ALWAYS check the source and interconnects before suspecting the amp.... I have been caught out this way a couple of times but never again I remember one time I couldn't get the R/H channel to fire up on a customers amp and was nearly tearing my hair out.... I went so far to replace almost ALL of the components on the board (again) as I couldn't see / measure anything obvious..... STILL nothing.... turns out it was the friggin' interconnect that had come apart inside phono plug

The other time "both" channels didn't work.... long story short, the CD player had packed in

If a V2 / V3 goes pop (both channels) you will definitely smell electrical burning as they all go in the same place (transistors and a few resistors) and they burn the board badly (think charcoal).... you will know if the amp has cooked itself, your nose will tell you

[PinkFloyd]

His work is perfect. I've seen the differences between his solder joints and those from the MF factory. The solder joints of MF have not the same quality.

Thank you Christian, that is a very nice thing to say. The actual MF soldering is fine but the solder they use leaves a lot to be desired... I don't know what type it is but when I recap V2 / V3 etc. you can literally "pull" the capacitors off the board.... it's as if their solder just "touches" the legs of the component and doesn't really "flood" into the joint.

They also solder using Canadian "pin witness" standards.... this is fine if you are doing a lot of in the field repairs as you simply desolder and the part falls out but I have found this type of joint to be pretty flimsy / unreliable (especially where there is movement such as RCA sockets, volume controls etc....)

I prefer to desolder the pad using a desolder pump...... fit the new component and bend the legs over flush on the pads so there is a "mechanical" connection between leg and pad.... I then flood in solder (@ 460 C) to ensure a pretty much bullet proof join... the hotter the tip the faster the solder melts and makes for a nice shiny joint (note: you are more likely to damage a component / produce a dry joint by applying "less" heat for "longer"......)

Mike.

[gommer]

Sept 4, 2011 19:09:04 GMT joethearachnid said:

Sept 4, 2011 18:52:20 GMT gommer said:

Then suddenly... bam, shotgun noise, finished. Turned out to be a very small (SMD) underrated ceramic capacitor that exploded. Took half the board with it by shorting (400V to ground). Don't you just love it

Pictures or it didn't happen.

(Incinerated PCB pictures are always fun)

-JoetheArachnid

Nah, i don't have a habbit of photographing failures. The board was physically ok, besides a PCB track that had acted as a fuse, but half the active components were ruined.

Funny and impressive sight looking at the surroundings of the burned track and cap with a magnifying glass