Scratching My Head w/ Crown CDi 4000

So I'll try to keep this brief. I have been trying to fix this amp that doesn't want to power on.. Yes I have read all the posts and seen the most common problem with this series is the cap 196 that is part of the start circuit. this was a design flaw from factory and changing it usually takes care of all the problems. No luck. What is making things the most difficult is that all the circuit is very small surface mount. It seems from measurements that I'm not getting the Kickstart signal that should occur with the SMP power supply. I'll attach schematic. Looking at page 6, power supply. All my measurements are referenced to V_BULKRTN. At power on I get ~168vdc across the main caps after the bridge. At TP31(C8) I get 0vdc. At the top of the resister divider feeding V_KSTART I have 168vdc and at the midpoint of resisters 84vdc. So testing the Zeners, D28, D29 in circuit both the 16v diodes test good .7vdc forward and open on reverse. The D25 tests good also in circuit. I also notice that I never get 30v_CTRL and thus no 15v_CTRL. That goes to alot of stuff. So that is a good start. One question where does the 30v_CTRL originate?? Is it the power transformer circuit at B6?? But that is the primary so not sure?
I have many years of repairing equipment but almost no experience with SMPS supplies. Understand just a little from Youtube. Anyway this is a very common problem with this line of Crown amps. But not the capacitor it usually is.

1694467983066.png 1694468040067.png


  • crown_xti4000_power_amplifier_sch.pdf
    1.4 MB · Views: 126
As there are a multitude of different topologies in SMPS, there is no single cure to fix them.
Remains the "hard" way...

Wel, how do I try to repair a SMPS...
I remove the transformer so there is a seperation between the primary and the secundary.
Check the transformer for shorts or broken windings.

Check for any burned traces or cold solderjoints on the primary and secundary side.

Check each component if they are ok.
The power transistors, -Fets have no shorts or the like?
Replace if needed.

Then I feed the needed voltages to each secundary circuit to see if there are no shorts or what ever.
If so, remedy them end repeat the test.
Now you're sure that the secundary is ok.

Let's go to the primary.

Here again try each primary low voltage circuit by applying the required voltage.

Then check the power circuit.


DC voltage after rectification of the AC input.

All ok? Insert the transformer. It should work now.

Mostly that is...
Good luck.