On my way to work, old but still sounding very sweet Punch 600a4 was playing perfectly fine through all 4 speakers. Cranked a volume a little up... BOOM!... static from rears, distorted sound from fronts... turned it of immediately... And, a smell of burnt voice coils from rears, of course 
(good thing, that not from fronts). Third time I see different older RF's doing the same damn thing
I have no idea what is dead inside, today's night I'll try figuring this out. Is there anything specific to look at these amps to have any kind of protection from these accidents? I never had these catastrofic failures with other brands
(good thing, that not from fronts). Third time I see different older RF's doing the same damn thing I have no idea what is dead inside, today's night I'll try figuring this out. Is there anything specific to look at these amps to have any kind of protection from these accidents? I never had these catastrofic failures with other brands
Under normal operating conditions, the amps should not be failing. If the amp had been recently repaired, something may have been missed (unmatched emitter resistors or unmatched output transistors, gate resistors out of tolerance, drivers leaking or open...). Any of these can cause failures under normal operating conditions.
The reason they burn coils is because of the DC offset. The offset is most often caused by shorted output transistors. The only protection is to shut down the drive circuit for the output transistors. This is done through over-current sensing. This typically protects the power supply (well.. it protects the ps about 50% of the time) but it offers no protection for the speakers.
You can protect the speakers by installing a large bi-polar capacitor in series with the speaker.
The reason they burn coils is because of the DC offset. The offset is most often caused by shorted output transistors. The only protection is to shut down the drive circuit for the output transistors. This is done through over-current sensing. This typically protects the power supply (well.. it protects the ps about 50% of the time) but it offers no protection for the speakers.
You can protect the speakers by installing a large bi-polar capacitor in series with the speaker.
Thank you for reply! It was repaired, front channel was blown, outputs + driver + a huge mess through all SOT23's there... This channel still works great
Very likely, some resistors on failed channel became unmatched... Someone used it bridged before. I'll check this out.
Bi-polar capacitor in series with speaker is an awesome idea!!! Please, let me know what capasitor would you recommend? I would cry
if some amp will torture my fronts.
Very likely, some resistors on failed channel became unmatched... Someone used it bridged before. I'll check this out.
Bi-polar capacitor in series with speaker is an awesome idea!!! Please, let me know what capasitor would you recommend? I would cry
if some amp will torture my fronts.Any cap that will not interfere with the low end crossover frequency for the speakers will work.
For example, if you have a high pass crossover frequency of 200Hz (via an electronic crossover) for the front speakers, you would want a cap that would cross the speakers at 200Hz or lower. For a 4 ohm load, you would need a cap of 200uf or more.
For example, if you have a high pass crossover frequency of 200Hz (via an electronic crossover) for the front speakers, you would want a cap that would cross the speakers at 200Hz or lower. For a 4 ohm load, you would need a cap of 200uf or more.
Even more puzzled right now...
Opened it - replaced 2 blown FET's, replaced drivers just in case, replaced gate and emitter resistors (these were so not matched...). Bench tested - all channels working. Put it in a car - works (except for my rear right speaker, which is blown and very noisy). Cranked volume - works... 15 minuts - no problem. Turned HU off - BAM! - same speaker loudly popped. Turned it on again - smoke from my poor speaker So it works, but when there is sharp change in input signal, FET's fails.. - no ideas in my head
Edit:
Disassembled it - everything ok. Bench tested - works!!! What can cause these DC spikes in output, which are killing speakers/FET's?
Opened it - replaced 2 blown FET's, replaced drivers just in case, replaced gate and emitter resistors (these were so not matched...). Bench tested - all channels working. Put it in a car - works (except for my rear right speaker, which is blown and very noisy). Cranked volume - works... 15 minuts - no problem. Turned HU off - BAM! - same speaker loudly popped. Turned it on again - smoke from my poor speaker
So it works, but when there is sharp change in input signal, FET's fails.. - no ideas in my headEdit:
Disassembled it - everything ok. Bench tested - works!!!
What can cause these DC spikes in output, which are killing speakers/FET's?One the bench, is there a pop in any channel when the amp is switched on or off?
If there is no pop, reverse the RCA left-right connections (in the vehicle) to see if the pop moves to another channel. If you're concerned that you'll damage a speaker, use a woofer or a junk speaker.
I wouldn't reconnect it to the defective speaker. A defective speaker could present a very low impedance which could cause the amp to fail.
If there is no pop, reverse the RCA left-right connections (in the vehicle) to see if the pop moves to another channel. If you're concerned that you'll damage a speaker, use a woofer or a junk speaker.
I wouldn't reconnect it to the defective speaker. A defective speaker could present a very low impedance which could cause the amp to fail.
Update:
It isn't working right on bench. If amp is cold, there is very powerful DC spike on initial startup (only in trouble channel), then DC goes down, then a little up and then back to zero and stays that way. I can adjust bias now.
Then if I run amp ander load, turn it off (it's warm now) then turn it on - there is full DC in channel without any spikes. Zero feedback to bias adjustments.
Fets replaced; drivers replaced; all gate/emitter resistor replaced. Even almost all SOT23's replaced. Still no go
MAGIC...
It isn't working right on bench. If amp is cold, there is very powerful DC spike on initial startup (only in trouble channel), then DC goes down, then a little up and then back to zero and stays that way. I can adjust bias now.
Then if I run amp ander load, turn it off (it's warm now) then turn it on - there is full DC in channel without any spikes.
Zero feedback to bias adjustments.Fets replaced; drivers replaced; all gate/emitter resistor replaced. Even almost all SOT23's replaced. Still no go
MAGIC...Do you have an oscilloscope?
Have you checked for broken leads on components or broken solder connections? If you can't see clearly due to flux or other debris, clean the board with acetone and a toothbrush. Do this outside with good ventilation.
Does the DC offset always swing the same way (to the positive rail or to the negative rail)?
Did you check the gate drive resistors after replacing the outputs? Measure from the gate lead of one transistor to the gate lead of the other parallel transistor. This should show 2x the resistance of a single gate resistor. It will also confirm that you have a good connection to the board from both transistors.
Did you check the 20 ohm driver resistors?
If none of this helps, get a schematic for the amp from Rockford and forward it to me.
Have you checked for broken leads on components or broken solder connections? If you can't see clearly due to flux or other debris, clean the board with acetone and a toothbrush. Do this outside with good ventilation.
Does the DC offset always swing the same way (to the positive rail or to the negative rail)?
Did you check the gate drive resistors after replacing the outputs? Measure from the gate lead of one transistor to the gate lead of the other parallel transistor. This should show 2x the resistance of a single gate resistor. It will also confirm that you have a good connection to the board from both transistors.
Did you check the 20 ohm driver resistors?
If none of this helps, get a schematic for the amp from Rockford and forward it to me.
Thanks, Perry! Board is very clean and I carefully inspected everything. I replaced all mentioned resistors, but I'll double check all readings again today.
There is still no scope on my work table I watched a several of them on ebay, but at the end they were bid up a way too much. Still looking.
I'll try getting schematic from Rockford. Layout of the board makes it extremely difficult, almost impossible, to compare channels. And much greater then average number of SOT23's only adds up...
I really appreciate your help
There is still no scope on my work table
I watched a several of them on ebay, but at the end they were bid up a way too much. Still looking.I'll try getting schematic from Rockford. Layout of the board makes it extremely difficult, almost impossible, to compare channels. And much greater then average number of SOT23's only adds up...
I really appreciate your help
update
Cleaned everything one more time - no effect, same DC spikes in one channel. Then I noticed a little sparks sometimes happening between voltage regulators heatsinks... Tried to bend them (with power on ) bam... one big spark and blown power supply FET's and LM339D voltage comparator Replaced everything... and it works!!!
Is it possible to have a disturbance in one channel due to unstable power supply? No spikes of DC right now, just clean sound.
Cleaned everything one more time - no effect, same DC spikes in one channel. Then I noticed a little sparks sometimes happening between voltage regulators heatsinks... Tried to bend them (with power on
) bam... one big spark and blown power supply FET's and LM339D voltage comparator Replaced everything... and it works!!!Is it possible to have a disturbance in one channel due to unstable power supply?
No spikes of DC right now, just clean sound.- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.