Good day everyone.
I have on the bench an amp board from DALI SUB E-12F. It is class D amp with a smps on the same board.
The issue is that it powers off way before the rated power is reached (the protection circuit kicks in). It has an independent standby power supply, which stays on after the main power supply is turned off via a relay on the primary side (thus there is no reason to believe that the protection is triggered from the smps IC on the primary side).
The normal value of the positive and negative power rails is +/- 43V.
The positive rail stays stable at +43V (+/- few volts when the bass kicks), but the negative rail goes down to -70 -80V on heavy bass and that triggers the protection. With no sound output both rails stay stable. The filter caps on that rails are 1000uF 63V. Out of the board they measure ~970/~950uF with .0 ESR. Switched the caps between the rails and still the same behavior.
The rectifier diodes and the amp mosfets were tested out of the board with a component tester and they seem to be fine and with identical values.
Any ideas what might be causing the negative rail to go down? If there was an excess load I would expect it to go up, close to reference, but can't figure out where that extra negative power is coming from.
Unfortunately I could not find schematics. Also, the amp seems to be using discrete class D amp circuit (no specialized class D driver IC like IRSxxxx, ICE.. or similar is used), one sound output and common ground for speaker and board. Also there is something that I haven't seen in other class D amps - there is a significant capacitance (~190uF) on the output - 4 electrolytes (68uf @ 160v) after the inductor. They are installed in two parallel series. Each couple is connected on the positive side and negative sides are connected to the amp output and ground (see attached doodle).
p.s. adding a couple of photos for visual aid
I have on the bench an amp board from DALI SUB E-12F. It is class D amp with a smps on the same board.
The issue is that it powers off way before the rated power is reached (the protection circuit kicks in). It has an independent standby power supply, which stays on after the main power supply is turned off via a relay on the primary side (thus there is no reason to believe that the protection is triggered from the smps IC on the primary side).
The normal value of the positive and negative power rails is +/- 43V.
The positive rail stays stable at +43V (+/- few volts when the bass kicks), but the negative rail goes down to -70 -80V on heavy bass and that triggers the protection. With no sound output both rails stay stable. The filter caps on that rails are 1000uF 63V. Out of the board they measure ~970/~950uF with .0 ESR. Switched the caps between the rails and still the same behavior.
The rectifier diodes and the amp mosfets were tested out of the board with a component tester and they seem to be fine and with identical values.
Any ideas what might be causing the negative rail to go down? If there was an excess load I would expect it to go up, close to reference, but can't figure out where that extra negative power is coming from.
Unfortunately I could not find schematics. Also, the amp seems to be using discrete class D amp circuit (no specialized class D driver IC like IRSxxxx, ICE.. or similar is used), one sound output and common ground for speaker and board. Also there is something that I haven't seen in other class D amps - there is a significant capacitance (~190uF) on the output - 4 electrolytes (68uf @ 160v) after the inductor. They are installed in two parallel series. Each couple is connected on the positive side and negative sides are connected to the amp output and ground (see attached doodle).
p.s. adding a couple of photos for visual aid
