Loud popping noises in one channel of my Phase Linear 400 alerted me to potential trouble, the meter was banging violently against its stop.
I disconnected the amp which has an original set of semiconductors and tried to measure the output dc.
Unfortunately it is an intermittent phenomena, the amp works like a charm on the bench, but I am reluctant to put it back in service.
The amp seems older, it has the serial number 2740 and the board has the designation 14A.
Since the intermittent behavior is probably not due to a semiconductor, I wonder what should be changed in the amp to regain confidence, so to speak.
Uwe
I disconnected the amp which has an original set of semiconductors and tried to measure the output dc.
Unfortunately it is an intermittent phenomena, the amp works like a charm on the bench, but I am reluctant to put it back in service.
The amp seems older, it has the serial number 2740 and the board has the designation 14A.
Since the intermittent behavior is probably not due to a semiconductor, I wonder what should be changed in the amp to regain confidence, so to speak.
Uwe
VAS transistor = voltage amplifier stage. It doesn't really come unsoldered, but the heat causes the connections to oxidize. Eventually the connection from the heat sink (collector connection) to the PCB fails. The 7.5k 1 watt resistor in the collector circuit gets fairly warm, too so that might be worth checking.
The Series 2's have a similar problem with the shunt regulators that feed the LF356 op amp. They get hot enough to discolor the PCB, in addition to the failures due to oxidation.
Any amp that's been around this long and seen a lot of use, and isn't forced-air cooled is going to have similar problems. But PL's topology has a really nasty habit of putting out large DC spikes when this stuff happens.
The Series 2's have a similar problem with the shunt regulators that feed the LF356 op amp. They get hot enough to discolor the PCB, in addition to the failures due to oxidation.
Any amp that's been around this long and seen a lot of use, and isn't forced-air cooled is going to have similar problems. But PL's topology has a really nasty habit of putting out large DC spikes when this stuff happens.
You can get the schematic here:
http://www.audio-circuit.dk/Schematics/Phase-Linear-400-pwr-sch.pdf
As saud, it's most likely a bas solder joint. With power on, try tapping carefully on the circuit board with the plastic back end of a screwdriver or similar tool to find the spot............
http://www.audio-circuit.dk/Schematics/Phase-Linear-400-pwr-sch.pdf
As saud, it's most likely a bas solder joint. With power on, try tapping carefully on the circuit board with the plastic back end of a screwdriver or similar tool to find the spot............
Well, I still don't know what you mean.
Many transistors on the pcb have their own little heat sink, and Q6 is off the pcb bolted to the chassis.
Nowhere in my amplifier is a 7.5k resistor (or I am blind!), so I am at a loss what you refer to, are you talking about a PL400 with the pcb 14A?
Uwe
Many transistors on the pcb have their own little heat sink, and Q6 is off the pcb bolted to the chassis.
Nowhere in my amplifier is a 7.5k resistor (or I am blind!), so I am at a loss what you refer to, are you talking about a PL400 with the pcb 14A?
Uwe
Well, I still don't know what you mean.
Many transistors on the pcb have their own little heat sink, and Q6 is off the pcb bolted to the chassis.
Nowhere in my amplifier is a 7.5k resistor (or I am blind!), so I am at a loss what you refer to, are you talking about a PL400 with the pcb 14A?
Uwe
Many transistors on the pcb have their own little heat sink, and Q6 is off the pcb bolted to the chassis.
Nowhere in my amplifier is a 7.5k resistor (or I am blind!), so I am at a loss what you refer to, are you talking about a PL400 with the pcb 14A?
Uwe
My bad, not all the boards are the same. It's 18k on one of my PLs, and 7.5k on the other two. And I've seen three different input stages over the years. Two diff stages, one diff stage, and an op amp. But everything following that is pretty much the same and I've seen the VAS (the 40327 or 40412) open up twice - once fatally. Any solder joint can fail upsetting the DC balance, but the usual suspects are those components that sit there and cook when the amp idles.
Jan Dupont said:
Boy did I find the spot!
I used your tapping technique as well as a temperature probe to see what ails one of my channels. I noticed Q5 was very hot (compared to the trouble free channel), about 70 degrees Celsius.
When I tapped Q7 there was a strong spark. It looked as it I had made a short between the transistor and its cooling fins, but of course that doesn't make sense, they are connected anyways. So I don't know what sparked there, the transistor was not bent or touching anything else. But now my channel shows only half a waveform the other half is lost, Q7 seems dead.
It wasn't the original anyways instead of the MM4003 I found a 2N5415, the other channel is original.
Also the AGX 5 fuses seem to have been changed and increased.
Now I need a cigarette and advise what to attempt next.
Uwe
A reason to that Q5 is getting so hot could be that Q7 was the reason to your problems. If Q7 had an intermittent internal short circuit, you would have the problems you described in post 1.
If you got a spark tapping on Q7 (originally a MM4003 in TO-39 case), you should not get a spark between the TO-39 case and the heatsink (unless the heatsink are touching other components or metal parts). The spike most likely came from one of the pins at the circuit board due to bad soldering.
Change Q7 and make a new test. I have attached the data for the MM4003. There are many Phase Linear threads in this forum with suggestions for replacement Q's.
If needed, contact me through PM.
If you got a spark tapping on Q7 (originally a MM4003 in TO-39 case), you should not get a spark between the TO-39 case and the heatsink (unless the heatsink are touching other components or metal parts). The spike most likely came from one of the pins at the circuit board due to bad soldering.
Change Q7 and make a new test. I have attached the data for the MM4003. There are many Phase Linear threads in this forum with suggestions for replacement Q's.
If needed, contact me through PM.
The 2N5415 is a suitable sub for MM4003 which is very hard to find. . The 2N5415 has a Vce of 200 and the 2N5416 is rated for 300 Vce. Either will work. 2N3440 or 2N3439 are suitable replacements for the the 40327.
If you have the 400 (with analog meters) check the numbers on Q3-Q4. If they are 2N 5401 they should be replaced. There is a service bulletin concerning this. You can view it on my site at Phase Linear bulletins. I have seen Q1 & Q2 become intermittent also.
You may want to consider installing an output relay for this amp. There is information on the site above for a relay board that connects directly to the output jacks.
If you have the 400 (with analog meters) check the numbers on Q3-Q4. If they are 2N 5401 they should be replaced. There is a service bulletin concerning this. You can view it on my site at Phase Linear bulletins. I have seen Q1 & Q2 become intermittent also.
You may want to consider installing an output relay for this amp. There is information on the site above for a relay board that connects directly to the output jacks.
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