I was looking at the Soundstream 6500 schematic, and noticed that ICF17:B doesn't seem to be described.
Would that be the reason why I'm seeing -12.8v on Pin7 of this Lanzar 6000D's ICF17? Its a JRC/TL072. I tried replacing all OpAmps and no change. All other pins and opamps are checking out OK.
On the PS side of things, I found the PS struggles and draws extra current (8A) when input voltage is less than about 12.2vDC, even thought the drive signal looked somewhat OK. The fix was to drop gate resistors from 100ohms down to 47ohms. Now the amp draws 2A even at very low voltage (10v) and the PS fets no longer get HOT. MJE172/182 drivers staying at ambient.
Output fets, IRFP360 (x16), driven also by MJE172/182, about half of them were found damaged, broken legs, or shorted, so I clipped all the bad ones and placed an order for a new full set.
Amp produces audio otherwise.
I'm really just looking for a second opinion on Pin 7 of ICF17. I tried tracing and continuity checking this pin to other components and I actually could not find any components connected to this Pin7, which looks similar to the SS6500D schematic. Perhaps this IC is just floating its B side output?
Would that be the reason why I'm seeing -12.8v on Pin7 of this Lanzar 6000D's ICF17? Its a JRC/TL072. I tried replacing all OpAmps and no change. All other pins and opamps are checking out OK.
On the PS side of things, I found the PS struggles and draws extra current (8A) when input voltage is less than about 12.2vDC, even thought the drive signal looked somewhat OK. The fix was to drop gate resistors from 100ohms down to 47ohms. Now the amp draws 2A even at very low voltage (10v) and the PS fets no longer get HOT. MJE172/182 drivers staying at ambient.
Output fets, IRFP360 (x16), driven also by MJE172/182, about half of them were found damaged, broken legs, or shorted, so I clipped all the bad ones and placed an order for a new full set.
Amp produces audio otherwise.
I'm really just looking for a second opinion on Pin 7 of ICF17. I tried tracing and continuity checking this pin to other components and I actually could not find any components connected to this Pin7, which looks similar to the SS6500D schematic. Perhaps this IC is just floating its B side output?
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The supply is regulated and when there is significant input voltage, the duty cycle is reduced so there is additional deadtime.
As the input voltage drops, the duty cycle increases to a point where both banks of FETs are on at the same time, causing increased current draw.
An easier solution is to replace two of the pulldown resistors (one for each output of the 494), with 1k resistors, replacing the 4.7k.
A lot of amps have unused op-amps. It's possible that that's what 17b is. Are pins 5 and 6 connected to anything?
As the input voltage drops, the duty cycle increases to a point where both banks of FETs are on at the same time, causing increased current draw.
An easier solution is to replace two of the pulldown resistors (one for each output of the 494), with 1k resistors, replacing the 4.7k.
A lot of amps have unused op-amps. It's possible that that's what 17b is. Are pins 5 and 6 connected to anything?
If I understand that correctly, you are suggesting changing out existing 4.7k for 1k pull down resistors? This amp actually appears to already be using 1k pulldown resistors. Comparison to the SSxxx6500D schematic, this Lanzar 6000D is using 4 (1k) pulldown resistors instead of 2 (4.7k) as shown on the schematic. Using 47ohm gate resistors helped immensely. The leading edge of the drive signal at low input voltage is exactly square whereas before wasn't so clean.
Pins 5/6 of ICF17 are not connected to anything.
Pins 5/6 of ICF17 are not connected to anything.
For all of this type of amp I repaired, going from 4.7k > 1k for two pulldown resistors was all that was needed. Maybe later amps need something else (using different FETs, deadtime, frequency...) but before someone replaces all of the gate resistors, they should try replacing only 2 pulldown resistors.
If 5/6 are unconnected, that half of the op-amp is unused.
If 5/6 are unconnected, that half of the op-amp is unused.
I'd like to think the 47 ohm gate resistors I've used as a positive though I did consider modifying the pulldowns originally.
See, this amp is arguable using non-flame resistant resistors on all 1/4w and 1/8w resistors everywhere. Such that as a fire hazard on any type of failure but most commonly seen in an amp's power supply, I feel more comfortable with the 47 ohm flameproof units I've affixed to this amp over the originals.
Being that this amp uses non-flame resistant resistors everywhere, it'll probably be the last type of this amp I care to repair anyways.
See, this amp is arguable using non-flame resistant resistors on all 1/4w and 1/8w resistors everywhere. Such that as a fire hazard on any type of failure but most commonly seen in an amp's power supply, I feel more comfortable with the 47 ohm flameproof units I've affixed to this amp over the originals.
Being that this amp uses non-flame resistant resistors everywhere, it'll probably be the last type of this amp I care to repair anyways.
What amps other than PG use flameproof gate resistors in the power supply?
The gate resistors are the least of the problem when the PS FETs fail.
The gate resistors are the least of the problem when the PS FETs fail.
Metal film vs carbon film. OK so not officially flame-proof. Just I've seen Carbon Film resistors actually glow red hot and catch actual fire than I have metal film resistors. This amp is almost exclusively using all carbon film resistors.
Next time I'll investigate pulldown modifications. Thank you
Next time I'll investigate pulldown modifications. Thank you
The coating is what typically makes them flame up or not. Paint coating (typically glossy) burns. A ceramic coating (typically dull/matte) generally does not burn.
It is true that the metal film/oxide resistors typically have a ceramic coating and carbon film typically have a paint coating.
Most amps use painted resistors which burn. This isn't generally a problem. In amps that have resistors with ceramic coatings, they are typically only used sparingly and typically only found in the output section. In class D, you will find them as gate resistors for the output transistors and in a few other locations. In other (linear type) amps, they are often used as source/emitter resistors.
This is just to clarify so that people aren't worried about repairing amps that have standard resistors.
It is true that the metal film/oxide resistors typically have a ceramic coating and carbon film typically have a paint coating.
Most amps use painted resistors which burn. This isn't generally a problem. In amps that have resistors with ceramic coatings, they are typically only used sparingly and typically only found in the output section. In class D, you will find them as gate resistors for the output transistors and in a few other locations. In other (linear type) amps, they are often used as source/emitter resistors.
This is just to clarify so that people aren't worried about repairing amps that have standard resistors.