CROWN XTi4000 AMP WON'T START

[bigdrums925]

Hello: Working on a Crown XTi4000 amp with SMPS. I had this starting up (booting) a few months ago and without using it at all when I tried to fire it up a week ago it would not. No lights, no current draw except for the initial surge, then none. I have the owners, service, and schematic. I will try to post them here. I also find voltages at the various test points. Maybe someone will give this a shot? Thanks! Can I upload a .PDF?
XTi_4000_schematic_138349-11_D_original.pdf

[Jazz P Bass]

You posted that you have the Service Manual.
The one that I have is 7Mb.
Too large to upload.

If you have that one, I would suggest that you read through it as the power supply is very sophisticated.
(As is the whole amplifier)

It is stated in the SM what the supply startup sequence is.

If there are any shorted output section components, the power supply will go into 'crowbar' shutdown.

[bigdrums925]

Like you said Jazz, it is sophisticated. I read the startup sequence before posting.
On pg 7 of the SM it details the startup sequence beginning with "apply 3.3v to power pins"
Not sure what power pins they are referring to however. Do you have some idea?

2nd step says "uC looks at TP17. If it is low enters bootstrap mode"
TP17 is merely a pinhole on the board as opposed to other testpoints being a raised clip.
Would placing a jumper from TP17 to ground insure it being "low"?

I will check the output devices but I was able to get the front panel lights to come on a few months ago
and never used the amp beyond testing so I believe they are still good.

And lastly it is the bootloader mode we want, correct?

[nickb]

Like you said Jazz, it is sophisticated. I read the startup sequence before posting.
On pg 7 of the SM it details the startup sequence beginning with "apply 3.3v to power pins"
Not sure what power pins they are referring to however. Do you have some idea?

2nd step says "uC looks at TP17. If it is low enters bootstrap mode"
TP17 is merely a pinhole on the board as opposed to other testpoints being a raised clip.
Would placing a jumper from TP17 to ground insure it being "low"?

I will check the output devices but I was able to get the front panel lights to come on a few months ago
and never used the amp beyond testing so I believe they are still good.

And lastly it is the bootloader mode we want, correct?

I think the flowchart on the next page is more relevant "Power Up sequence for CEquel". The take away from that chart is that if Vcc is too high the PSU is shutdown. The other one only applies after the power rails are up. You don't want to enter the bootloader as that is for updating the firmware.

Among the many monitoring functions, I'll wager there is a check for the DC offset on the power amp output. If there is an offset the PSU will be shut down. The shut down method seems to be done by killing the +15V_CTL rail via U16. And all that is just a long way round of saying to do as Jazz said - check the power amp output transistors.

[bigdrums925]

Checked the output transistors with no shorts or abnormal measurements detected. This was done with them still mounted.
Taking a look at the "Power up sequence for CEquel" it is much more confusing to me. I see the logic of it, but don't know how
to verify each step. Please advise.

[Jazz P Bass]

I would definitely start on page 22: "Misc notes for root cause & diagnosis ideas for repairs"

[Jazz P Bass]

Checked the output transistors with no shorts or abnormal measurements detected. This was done with them still mounted.
Taking a look at the "Power up sequence for CEquel" it is much more confusing to me. I see the logic of it, but don't know how
to verify each step. Please advise.

Page 25: "Initial Startup".
Do you have +15V_ Cntrl at TP 28? (Page 75)
For that matter, do have "V_ Bulk"?

[g1]

The one that I have is 7Mb.
Too large to upload.

Did you try? The limits were increased recently, though I'm not sure to what amount:
http://music-electronics-forum.com/t29765/#post469351

[bigdrums925]

I do not have +15V at TP28, only about .2V

I tried looking up what V_Bulk means but still don't know.

Having previously removing the board to test the output transistors, I put it back in the chassis to test for the
+15V at TP28 and this time it started up, display shows initially CROWN then says DSP OFF and the ready lights
come on after about 20 seconds. Haven't tested for operation yet.

Your thoughts?

[bigdrums925]

Looks like it's working now. seems that the screws holding the heatsinks down to the chassis must be insulated.
I had to fab them from some plastic stock on my metal lathe.
Would still like to know what V_Bulk is though

Thanks for all the time and consideration and the help making this amp useable.!

[Jazz P Bass]

Did you try? The limits were increased recently, though I'm not sure to what amount:
http://music-electronics-forum.com/t29765/#post469351

I forget what it said when I tried.
I think the limit is 4.7Mg

[Jazz P Bass]

[QUOTE=bigdrums925;471291]Would still like to know what V_Bulk is though.QUOTE]
Look on the schematic/ Page 75.
The mains comes in from the left, gets filtered, then it goes through a bridge rectifier & becomes "V_Bulk".
It's the main dc voltage that the smps will be switching.