I have an old school earthquake 6 channel amp (power house) that has two channels down.
Power supply section is good so I removed the D998/B778 combo on one of the bad channels to find the input is negative rail volts. If I put a 50hz sine to the RCAs for those channels I get a 50hz square wave at the removed transistors input (Full rail voltage) and when stopped its sits at negative rail volts. I cant find the schematics for the board and Im just starting out in amp repair as a hobby, so any help is greatly appreciated.
Thanks guys
Power supply section is good so I removed the D998/B778 combo on one of the bad channels to find the input is negative rail volts. If I put a 50hz sine to the RCAs for those channels I get a 50hz square wave at the removed transistors input (Full rail voltage) and when stopped its sits at negative rail volts. I cant find the schematics for the board and Im just starting out in amp repair as a hobby, so any help is greatly appreciated.
Thanks guys
If the amplifier as usual has negative feedback around it, and being the loop open because of the absence of this transistors, seems ok to me to find square waves in place of proper sines, and that the output steady voltage takes any undefined voltage.
How are the two channels 'down'?
Was the negative rail voltage present on the speaker output before you did any work on the amp?
If not, what were the conditions when you did read rail voltage?
Was the negative rail voltage present on the speaker output before you did any work on the amp?
If not, what were the conditions when you did read rail voltage?
Both channels have no sound, they are channels 1 and 2 and are run from the same RCA input. I have now replaced the B778/D998 pair and have the following on each pin.
Base - a square wave from Neg rail to 0v when a sine is applied to the RCAs or Neg rail v with no signal applied
Collector - Neg rail or positive rail (D998 + and B778 -)
Emitter - B778 has the same square wave as above when signal is applied and Neg rail v with no signal. D998 has a small top half of a sine with a signal applied.
Base - a square wave from Neg rail to 0v when a sine is applied to the RCAs or Neg rail v with no signal applied
Collector - Neg rail or positive rail (D998 + and B778 -)
Emitter - B778 has the same square wave as above when signal is applied and Neg rail v with no signal. D998 has a small top half of a sine with a signal applied.
Do you have any DC offset on either channel (measured directly across the two speaker terminals for the channel) with all components installed?
would anyone have a schematic for a 6 channel powerhouse earthquake amp.
or even a lead on how to get one
Thanks for any help
or even a lead on how to get one
Thanks for any help
I didn't see your reply on Saturday.
Is this amp bridgeable?
If so, post a photo of the speaker terminals and make a note of the two dead channels as they are marked on the terminals.
Is this amp bridgeable?
If so, post a photo of the speaker terminals and make a note of the two dead channels as they are marked on the terminals.
Hi Mate, yes its bridgeable (each set of two channels) do you want a pic of inside the amp of the connections or the actual screw connectors
Thanks
Thanks
At least, the screw terminals so I can see how they're labeled. I need you to try wiring it a bit different than normal and need to see the markings so I can tell you how to wire it.