Phase Linear D500 (only a small breakdown remains)

[Domoticloud]

Hello to all technicians and audiophiles who, like me, love "Phase Linear" amplifiers.
I have a D500 (dual 500) that works, but once turned on with its "Power" button, it won't turn off!?...
You have to unplug the power cord, and after a few minutes, plug it back in, it stays off, until... you press the "Power" button again to turn it back on.
Are you familiar with this problem?

For information and for those who are unfamiliar with this large D500 model:
The Power button is part of a circuit board, which controls the three power and/or protection relays.
The "Mains" power does not pass through this "Power switch."

Thank you in advance for all your feedback.


Bonjour à tous les techniciens et audiophiles qui aiment, comme moi, les amplis "Phase Linear". Je possède un D500 (dual 500) qui fonctionne, mais qui, une fois allumé avec son bouton "Power", ne veux plus s'éteindre !?...
Il faut enlever la prise et après quelques minutes, en remettant la prise il reste bien éteint, et cela, jusqu'au moment où... on active à nouveau le bouton "power" pour le rallumer.
Connaissez-vous ce problème ?
Pour info et pour ceux qui ne connaissent pas ce gros modèle D500:
Le bouton Power fait partie d'une carte électronique, qui pilote les trois relais de puissance et/ou de protection.
Le "Secteur" ne passe pas par ce "commutateur Power"

Merci d'avance pour tous vos retours.

 

[wattsabundant]

The schematic for this amp is nearly impossible to read and understand. There is a time delay relay on the transformer primary acting as a soft start. Q508 controls the relay. I would check it.

 

[Domoticloud]

Thank you for your feedback. I have already replaced this MPSA42. The old one had an hfe of 80 and the new one (NOS Mpsa42) has an hfe of 100. Changing these two transistors Q508 and Q505 did not eliminate the fault. The amp turns on fine with the Power button, but if you press the switch again to turn it off, the amp stays on...

 

[TimD]

Myself, I'd grab a voltmeter and start at the relay and work back towards the switch. Despite the obscurity on the schematic, that circuit does not appear to be terribly complex, and I would think that the fault would reveal itself rather quickly.

You also mentioned blurry schematics . . . the D500 service manual at thecarversite.com has a pretty decent image if you have not see that one.

 

[eykensf]

I had this problem and I replaced the button itself and the issue was fixed. It is a mechanical problem. I found the latching switch on eBay : https://www.benl.ebay.be/itm/253756288609

 

[Domoticloud]

Despite the Off>On ignitions and to my great surprise…! It was apparently the ALPS push button that was failing to prevent it from turning off (yet measured and “inside slides clean” after disassembly)?! The fault was finally in front of my nose but I didn’t want to believe it. Now there remains the small problem of the left “LED bar” to repair because after switching on, the “Red Dot” comes to stand on -40db. instead of zero (small short circuit when handling the card because the 25mF 150v chemical always remains charged!)