Hello
I'm working on a t2500-1bd (not the constant power version). This amp had 2 bad output FETs and a bad PNP at the gate that pulls down the drive signal. After replacing them with used, but good parts (to test) the amp powers up and plays music fine. The issue comes when I turn the volume up with a speaker connected. The amp will seemingly turn off with a brief second and come back on, before the amp turns off it is drawing about 10amps of power, sometimes it is a little bit more/less. When this happens, I see the protect light come on and then turn off when the amp comes back on. I've tried 1ohm and 2ohm speaker configurations with same results.
If I remove the speaker and run the amp with no load, I can drive the amp into clipping (about 200 volts peak-peak) without any issues. The HV rail test point is reading about 108-110V at idle. With a speaker connected and playing music, it will drop to around 93V before the amp turns off.
The +/-25V rails (RF schematic calls it +LV_CLEAN and -LV_CLEAN), looks stable before the amp turns off as well. Gate drive to power supply FETs look normal until the amp turns off.
DC offset is <50mV
DC voltage at the power input terminals when the amp turns off is no less than 13.20V.
Playing a 40Hz tone with a speaker attached and my oscilloscope looking at the output of the amp. The sine wave looks nice and clean up to the point it turns off.
I think the issue is on the BD power supply card. Maybe some noise is getting onto the protection circuit when high current is present? Anyone have the schematic for the BD PS card? Or potentially know any specific components to check?
I also noticed I sometimes get a slight hum at the speaker with RCAs connected to the amp with no audio playing. Sometimes it goes away.
I'm working on a t2500-1bd (not the constant power version). This amp had 2 bad output FETs and a bad PNP at the gate that pulls down the drive signal. After replacing them with used, but good parts (to test) the amp powers up and plays music fine. The issue comes when I turn the volume up with a speaker connected. The amp will seemingly turn off with a brief second and come back on, before the amp turns off it is drawing about 10amps of power, sometimes it is a little bit more/less. When this happens, I see the protect light come on and then turn off when the amp comes back on. I've tried 1ohm and 2ohm speaker configurations with same results.
If I remove the speaker and run the amp with no load, I can drive the amp into clipping (about 200 volts peak-peak) without any issues. The HV rail test point is reading about 108-110V at idle. With a speaker connected and playing music, it will drop to around 93V before the amp turns off.
The +/-25V rails (RF schematic calls it +LV_CLEAN and -LV_CLEAN), looks stable before the amp turns off as well. Gate drive to power supply FETs look normal until the amp turns off.
DC offset is <50mV
DC voltage at the power input terminals when the amp turns off is no less than 13.20V.
Playing a 40Hz tone with a speaker attached and my oscilloscope looking at the output of the amp. The sine wave looks nice and clean up to the point it turns off.
I think the issue is on the BD power supply card. Maybe some noise is getting onto the protection circuit when high current is present? Anyone have the schematic for the BD PS card? Or potentially know any specific components to check?
I also noticed I sometimes get a slight hum at the speaker with RCAs connected to the amp with no audio playing. Sometimes it goes away.
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Perfect into 4 ohms up to clipping?
What are you using for a 12v supply?
Are you 100% sure that it's not dipping instantaneously well below 13.2v?
Side note, LV protection is sensed through the remote wire.
Do you have all of the screws back into the bottom backing plate and all tight?
What are you using for a 12v supply?
Are you 100% sure that it's not dipping instantaneously well below 13.2v?
Side note, LV protection is sensed through the remote wire.
Do you have all of the screws back into the bottom backing plate and all tight?
Hi Perry, it turned out to be not having the screws holding the board onto the casing. Once I put those in, the amp plays without cutting off now. The ground planes on the board without the screws probably isn't rated for the power levels and caused voltage drop in certain areas causing it to cut off.
Thanks for your help!
Thanks for your help!
They use the screws as part of the design in other amps as well. The T20001bd is the best example. Many of the connections are made through nothing other than the metal backing plate.
