Alpine MRV-F300S

Dr Zeus · 7th June 2011, 04:49 AM

Got this amp in for repair. I noticed some connection problems under the PCB for the RCA and fixed. Upon power applicaiton, the amp appears a slight attept at powering up but fails and powers off no more than 1/4 second later. Measuring with the scope I see the amp pulse a +10v wave at the fets. I can also observe a very brief ~+-60vDC on the center legs of the rectifiers. I'm guessing this amp is tethering in/out of protection as several pins of the TL494 pulse every ~4 seconds

Perry Babin · 7th June 2011, 04:51 PM

Do you see a pulse of DC on the bridging speaker terminals of any channel as the amp goes in/out of protection?

Dr Zeus · 8th June 2011, 04:12 AM

There is something wrong with chanel 2 (This is a 4 channel amp) where I can observe a +-20v severely clipped sine wave with no signal input to the amplifier. The outputs for channel 2 are Q211 and Q212 and they are not measuring shorted.

Dr Zeus · 8th June 2011, 04:30 AM

i just found C205, a yellow mylar cap near some of the opamps with a bad solder joint which I just fixed. Now I cannot get channel 2 to pulse anything on the scope more than just insignificant DC. All channels have +-.2vDC of pulsing activity on them. Amp still power cycles like before.

Dr Zeus · 8th June 2011, 12:51 PM

TL494

Pin 1: 0
Pin 2: 0.882
Pin 3: 0.090
Pin 4: 4.97 (Drops to ~2.5-3v every ~4 seconds)
Pin 5: 1.684
Pin 6: 3.738
Pin 7: 0
Pin 8: 13.74
Pin 9: ~0 (Pulses to .5v)
Pin 10: ~0 (Pulses to .5v)
Pin 11: 13.74
Pin 12: 13.74
Pin 13: 5.05
Pin 14: 5.05
Pin 15: 5.05
Pin 16: 0.001

Dr Zeus · 8th June 2011, 01:54 PM

When pulsing, the center leg of Q509 (a 5KF10P20FR) hits -40vDC momentarilly. On the other hand, Q508 (a 5JF10P20F) only hits about 12vDC before rocketting back to 0v.

Dr Zeus · 02:50 PM

Quote:

Do you see a pulse of DC on the bridging speaker terminals of any channel as the amp goes in/out of protection?

Referencing amp general ground pulse of -15vDC is on all speaker terminals. Referencing RCA shields I see no more than about -0.150vDC on speaker terminals. Referencing non-bridging speaker terminals or RCA shields I see +-20vDC on the center legs of the main rectifiers; D508 D509. Also I meant to say D508/D509 in my previous post, not Q.

Perry Babin · 8th June 2011, 03:10 PM

Can you post a photo of the inside of the amp. I have no information on this amp.

In general, there is an isolation between the primary and secondary grounds. When the secondary ground is pulled away from the primary ground, the problem is often a protection circuit component. Typically it's a PNP transistor with it's emitter connected to the positive rail (or sometimes to 5v) and it's collector connected to something near the power supply IC. You may have a problem like this.

Dr Zeus · 8th June 2011, 03:34 PM

I like the "army" of opamps.

Dr Zeus · 8th June 2011, 03:41 PM

Heres some pictures of the back of the PCB where identifications are easier to read.

7th June 2011, 04:49 AM	#1
Dr Zeus diyAudio Member Join Date: Oct 2010	Alpine MRV-F300S Got this amp in for repair. I noticed some connection problems under the PCB for the RCA and fixed. Upon power applicaiton, the amp appears a slight attept at powering up but fails and powers off no more than 1/4 second later. Measuring with the scope I see the amp pulse a +10v wave at the fets. I can also observe a very brief ~+-60vDC on the center legs of the rectifiers. I'm guessing this amp is tethering in/out of protection as several pins of the TL494 pulse every ~4 seconds

7th June 2011, 04:51 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Do you see a pulse of DC on the bridging speaker terminals of any channel as the amp goes in/out of protection? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

8th June 2011, 03:10 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Can you post a photo of the inside of the amp. I have no information on this amp. In general, there is an isolation between the primary and secondary grounds. When the secondary ground is pulled away from the primary ground, the problem is often a protection circuit component. Typically it's a PNP transistor with it's emitter connected to the positive rail (or sometimes to 5v) and it's collector connected to something near the power supply IC. You may have a problem like this. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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8th June 2011, 04:12 AM	#3
Dr Zeus diyAudio Member Join Date: Oct 2010	There is something wrong with chanel 2 (This is a 4 channel amp) where I can observe a +-20v severely clipped sine wave with no signal input to the amplifier. The outputs for channel 2 are Q211 and Q212 and they are not measuring shorted.

8th June 2011, 04:30 AM	#4
Dr Zeus diyAudio Member Join Date: Oct 2010	i just found C205, a yellow mylar cap near some of the opamps with a bad solder joint which I just fixed. Now I cannot get channel 2 to pulse anything on the scope more than just insignificant DC. All channels have +-.2vDC of pulsing activity on them. Amp still power cycles like before.

8th June 2011, 12:51 PM	#5
Dr Zeus diyAudio Member Join Date: Oct 2010	TL494 Pin 1: 0 Pin 2: 0.882 Pin 3: 0.090 Pin 4: 4.97 (Drops to ~2.5-3v every ~4 seconds) Pin 5: 1.684 Pin 6: 3.738 Pin 7: 0 Pin 8: 13.74 Pin 9: ~0 (Pulses to .5v) Pin 10: ~0 (Pulses to .5v) Pin 11: 13.74 Pin 12: 13.74 Pin 13: 5.05 Pin 14: 5.05 Pin 15: 5.05 Pin 16: 0.001

8th June 2011, 01:54 PM	#6
Dr Zeus diyAudio Member Join Date: Oct 2010	When pulsing, the center leg of Q509 (a 5KF10P20FR) hits -40vDC momentarilly. On the other hand, Q508 (a 5JF10P20F) only hits about 12vDC before rocketting back to 0v.

8th June 2011, 03:34 PM	#9
Dr Zeus diyAudio Member Join Date: Oct 2010	I like the "army" of opamps.

8th June 2011, 03:41 PM	#10
Dr Zeus diyAudio Member Join Date: Oct 2010	Heres some pictures of the back of the PCB where identifications are easier to read.

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