Smoke firing up ZenV4... help

[rebojorge]

Ok.... so I have been gathering the parts for quite some time now and finally it is getting to the test phase.

So I conected one channel to a Variac ... forgot to fuse it...

and started to turn it up slowly.... Voltage across R0 .6, good .... turn it up a little more. I was suppling about 100 V AC and voltage across R0, about .7 ... ok, sinks ... getting warmer, nice, but the unregulated suply was only about 42 Volts.... so I turn it up until I got 50 V unregulated supply (wich was suppling about 140 AC to the primary of the trafo), a little bit after that... .look those pretty colors, I didn´t know a resistor could glow!!! ... so I turned it of.

R0 buned.... R1.. probably, (it is not as dark but it is brownish)

So now I am in the process of getting some replacements, and want to know.... What else could have gone?

Also, I am a bit confused... when I was getting about 43 Volts unregulated supply, I measured about 36 VAC on the AC legs of the bridge..... Shouldn´t this give somithing closer to 50 V unreg.?

Thanks.... I will order the parts and probably play with the other channel in the meantime..... pictures of the process will follow.... (in about a month since I am going on a trip for work)

[Netlist]

This is bad news, but carry on.
Like Nelson says: go and drink a Corona, give it a rest and check for bad connections, wrongly connected fets and so on.
Next time, don't push the variac so far at first and measure all voltage carefully.
Have a nice trip and keep us posted.

/Hugo

[rebojorge]

I did... put it all away and drank half a bottle of wine to calm myself down. I´ll probably won´t test it again until I am back.

What I want to know right now is, Aside from R0 and R1, Are there other components that might have been damaged? I will be ordering tomorrow, and don´t want to be missing something when I get back.

Thanks.....

[till]

Are there other components that might have been damaged?

The Transistors.

stay calm, you are not the first expirencing this when building ZEN V4....

[rebojorge]

all right!! ... so it has been a few coronas, few months, + a girlfriend, - that girlfriend ... and now back to spending my evenings on my own.... well at least I will have some time to get this thing working.

I decided to leave that burned channel alone and try again with the untouched one. I wired up everything... I did fuse it this time, and followed the procedure, after about one hour the hottest transistor was abour 140 C ... the sinks I don´t know, but was able to touch them for about five seconds... (is this temp safe?)...
I then conected it to a cheap speaker... and hey... music!!! so the Zen is singing now... and I measured all the voltages in the schematic... all close but not too close... so I want to check with the rest of you here see what you think.

0.69V across R1 and R0
46.5V at the + of C9 (instead of 46... close enough)
39.5 at the Source of Q5 (instead of 42 ... ???)
39.7V on C7 (41 on the schem.)
23V on the Drain of Q1 (as oposed to 22)
3.26 on the Source of Q4 (instead of 4V)
3.39 Source to Gate on Q1 (schem 4V)
3.48 S to G on Q2 ... (4V)
34.1 at the R11, R12 node ... (schem 32V)

So ... non of the values is on the mark... all seme to be within a couple of Volts ... some higher, and most of them lower. Is this normal? Am I missing something? ... should I readjust R4?

Once I know I have this channel working, I will debug the other one.... then the chasis

thanks all

[rebojorge]

am I good to go? ... .Nelson? ... anyone??

[Netlist]

rebojorge,
You are doing just fine. I recall when building my ZenV4 proto the values were even more out of specs but all was fine.
From memory R4 sets the bias and something like 2A is about right.

Carry on with the burned channel. Probably the power mosfets and maybe also the regulator will have to be replaced.

Edit: One thing: 140°C is way too hot. Are you sure?
Are the mosfets well connected to the heatsink?

/Hugo

[rebojorge]

Thanks Hugo....

I will go on to the second channel.

and yes... 140 on the MOSFET ... they are not mounted perfectly yet... actually I am still trying to figure out how to do it best. Right now they have a mica insulator and no grease .... I am thinking about silpads ... Will the thermal conductivity increase? ... does anyone know of a supplier?

[Netlist]

rebojorge,
Do apply grease. The mica's are perfect material. Many would envy you to have them as they are not easy to get (anymore). It's very important to take your time to do this mechanical job in an accurate way.

/Hugo

[rebojorge]

ok then... I will apply grease.

and let you know what happens.
thanks