Fender Passport Event SMPS won't start up

[Delta362]

I'm working on a Fender Passport Event that won't power up. SMPS are not my strong suit. I get the +/-170VDC after the input bridge so no fuse is blown, but it doesn't appear that the PWM controller chip is starting up. I've disconnected the power amp and preamp circuits, but am having trouble solving this.

I've confirmed the startup resistor is good, caps and other components directly around U502 circuit are also good, including proper continuity to rule out bad solder joints. Voltages to the U502 ICE2B365 are as follows:
1: -166.9 VDC
2: -166.5 VDC
3: -166.7 VDC
4: +166.8 VDC
5: +168.8 VDC
6: N/C
7: -156.7 VDC
8: -166.7 VDC

Looking at the datasheet for the ICE chip, it seems that it wants 13.5V to get started, but I'm only getting around a 10V differential to it (pin 7 to pin 8). The zener Z507 checks ok on diode test function of my meter. What should I be checking next?

[Jon Snell]

What have you got on pin 8 of the transformer; it hould be pulsing with respect to AC Ground NOT normal ground. Around 470kHZ ish.

[Delta362]

What's the best way to have my scope read that? I understand that my AC ground (pin 8) is sitting at -170VDC, and the chassis is sitting at 0V. What's the best and safest way to check that signal with my scope? (Rigol 1052E)?

[Jon Snell]

Basic requirement is an isolated mains supply rated at twice the power requirement of the power supply.
This is a must as nothing can be measured without that basic requirement.


Plug the power supply input into the isolated mains. Connect your Earthed oscilloscope to the mains ACGND and scope the test point as shown.

[Delta362]

Thanks for the clarifications and notes, Jon! I'll get myself an isolation transformer before proceeding. I'll reply back once I can safely take those measurements.

[sugeda]

Check approximately 12v on pin7 of the U502.

[Delta362]

I'm not getting any AC waveform on pin 8 of the transformer with respect to ACGND. I measure <0.2ohms for the winding so it's not an open winding.

I'm getting 10.3VDC from pin 7 to pin 8 of the ICE chip U502.

[Jon Snell]

If there is more than 9volts on U502, it will oscillate if it is not faulty.
I would check R543 before condemning the chip.

[Delta362]

R543 is good. Got a suggestion on a replacement chip since the ICE2B365 is obsolete?

[Delta362]

I found this one. Looks to be similar specs and available.
https://www.mouser.com/ProductDetail...E3BR0665JXKLA1

[Jon Snell]

I would order one from Fender. If no longer available, maybe this one will work. A bit like the TOP*** chips.

[Delta362]

Fender does not have them available anymore. I found a few other types that look closer, but have a minimum order of a few hundred.

https://www.mouser.com/ProductDetail...2BcphYrA%3D%3D

One of the problems I found on the newer versions is the topology is different as the ones in stock didn't use the startup resistor. I was looking for flyback type. Would I need to remove components on my board, or something else if I subbed in either the ICE3BR0665JXKLA1 or ICE3A2565?

Is there a surface mount version in existence? if so, perhaps I could mount it on an SMT to DIP8 socket board adapter.