HELP: Zen V4 blowing fuse (and smoke as well)

jag · 17th November 2002, 04:24 AM

Phew, everything connected finally... Fuse set to 1.5Amp, powered up with 150W bulb in series - about 75 volts across the transformer primary and 20 volts at unregulated supply output. R0 measures about .6V. So far so good.

Connected directly to the mains (120V across the transformer primary). Fuse blows (1.5A) - a whiff of smoke around the power resitor area (not sure which one). Increase fuse to 2A - switch on - fuse blows again with a whiff of smoke - looks like it is R0 this time. Want to make sure which resistor is heating up - increase fuse to 3A - switch on - R0 & R1 are red hot (quite a bit of smoke) - immediately switch off - looks like they survived. The fuse did not blow up this time.

Here is the board picture - discoloration can be seen on R0 & R1. Any help greatly appreciated. Thanks...

jag · 17th November 2002, 04:26 AM

Here is the power supply. 47.5K bleeder resistor on the supply rails.

jag · 17th November 2002, 04:27 AM

Transformer primaries...

jag · 17th November 2002, 04:14 PM

Quote:

From Zen4 article:
If the voltages all check out then you have a 95% chance that everything is proper.If not,it is time do start doing your detective work.This is best done slowly. Wait till the next day.

I took the advice (it was past midnight anyhow). Connected the 150W bulb back in series (fuse set to 1.5A) and switched it on. This time the bulb glows only for the inrush current = open circuit (very small current flowing). Indeed, the primaries are at 125V and unregulated voltage is 50V. The voltages are shown below. Looks like Q2 is blown. I can change it (will have to wait for digikey UPS delivery). But, the question now is: why did it blow at 50V when it was working fine at 20V (what was causing such high bias currents to flow so that R0/R1 will glow redhot). Any ideas? Q3 seems fine with diode tester. R0/R1 measures 1.4ohm. Maybe I should fire up the other channel (with 150W bulb in series) and measure all the voltages rather than just the R0 voltage...

MikeW · 17th November 2002, 05:25 PM

Are you using IRFP044? They are only rated for 55 volts and you are very close to that. It looks like you did blow up your mosfets. Try IRFP140's. If you need a couple I may have a few. Good luck, Mike.

jleaman · 17th November 2002, 05:41 PM

nice boards im going to perchase a set now for my computer. : O ) ill power a set of nice litte speakers for awsome sound.

jag · 17th November 2002, 06:02 PM

Quote:

Originally posted by MikeW
Are you using IRFP044? They are only rated for 55 volts and you are very close to that. It looks like you did blow up your mosfets. Try IRFP140's. If you need a couple I may have a few. Good luck, Mike.

Well it is showing 54V since there is no load on the transformer. Just fired up the other channel, and all the voltages match up

. The unregulated voltage under load is 48V. Next: mono music from Zen4 after 1 hour of initial burn-in.

jag · 17th November 2002, 06:04 PM

Quote:

Originally posted by JasonL
nice boards im going to perchase a set now for my computer. : O ) ill power a set of nice litte speakers for awsome sound.

Yeah, yeah you can laugh at my expense...atleast you are in a good mood

jleaman · 17th November 2002, 06:12 PM

im not realy in a good mood as i cant get my heat sinks machined till my friend gets back : O ( and i dont have my new puter yet.. : O (

jleaman · 17th November 2002, 06:48 PM

This is the message:

Jason, would you mind asking "Jag" to email me Help@passdiy.com, If he has trouble getting the replacement parts I can help. R0 R1 have obviously had too much current pulled through them.

Thanks for the favor.
karen

17th November 2002, 05:25 PM	#5
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	Are you using IRFP044? They are only rated for 55 volts and you are very close to that. It looks like you did blow up your mosfets. Try IRFP140's. If you need a couple I may have a few. Good luck, Mike. __________________ MikeW

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17th November 2002, 05:41 PM	#6
jleaman Banned Join Date: Apr 2002	nice boards im going to perchase a set now for my computer. : O ) ill power a set of nice litte speakers for awsome sound.

17th November 2002, 06:12 PM	#9
jleaman Banned Join Date: Apr 2002	im not realy in a good mood as i cant get my heat sinks machined till my friend gets back : O ( and i dont have my new puter yet.. : O (

17th November 2002, 06:48 PM	#10
jleaman Banned Join Date: Apr 2002	This is the message: Jason, would you mind asking "Jag" to email me Help@passdiy.com, If he has trouble getting the replacement parts I can help. R0 R1 have obviously had too much current pulled through them. Thanks for the favor. karen