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J

jo shua

Guest
On Wednesday, 4 March 2015 at 02:30:16 UTC, palli...(edited) wrote:
Hi,

recently, a regular customer brought in his QSC PL-9, a \"9kW\" beast of an amp.

The model was first released nearly 20 years ago, as the flagship of the PowerLight range. My customer\'s example sat in its box until about two years ago when he purchased it and had it shipped to Sydney from the USA.

The model is no longer sold or supported by QSC and was never sold here. Its smaller brother (the PL-6 ) was sold here but is now similarly orphaned..

I agreed to have a look and found that one channel had simply stopped with no signs of serious damage - ie no blown fuses.

The amp consists of four, large modules - two PSUs and two amplifiers stacked on top of each other in pairs and crammed into a 3RU steel box. Access is just terrible and one needs the service manual just to find out how to get the modules out.

Eventually I did and still found no signs of damage, no power devices were shorted or tracks blown and it all looked fine. Next, I transferred the amp module from the dead channel onto the PSU of the working one and it ran just fine. So, it had to be a faulty PSU module.

The PL-9 has the weirdest circuitry I have ever seen, the SMPS is massive and claimed to be PFC but there is no PFC stage involved. What QSC did was to modulate drive to the power switching stage in proportion to the AC voltage at any moment, smoothing out the current draw but without the ability to regulate the resulting DC voltages. It works well enough, as I could see from the good channel. The SMPS produces four DC voltages: 50,100,150 and 200 volts all positive. Max current on the 200V rail is 25amps !!!

Each amplifier is a bridge mode pair with one output grounded - not so unusual until you realise the DC supply jumps in three steps from +50V to +200V in line with the audio signal. QSC have included an elaborate scheme to correct the anomalies this generates and it appears to work.

My customer tried to source a new PSU module here and was told the last selling price was $2500 - but with none available. He might however take advantage of QSC\'s cash rebate deal. Anyone who buys a new PL380 from an authorised dealer is entitled to an US$800 rebate from QSC, if they return a PL-9 or PL-6 to the factory. No requirement that it be in working order is mentioned.

The PL380 is rated at 8kW and is of conventional class D design with no PFC in the SMPS. It is built on a single PCB and amazingly there are only *six* active power devices in the whole amp, compared to several dozen in the PL-9.

Anyhow, I persisted with the faulty PSU a bit longer, running it on the bench on its own from my iso tranny. It did not start up but I could tell an auxiliary switching PSU was pulsing, trying to start up. Making a one turn loop with the ground clip linked to the tip of a scope probe and dropping it over the tiny transformer I saw bursts of HF every 120mS or so. This auxiliary PSU develops a series of low DC voltages to run the daughter board on the main SMPS, +5, +/-15 etc.

If it does not run - nothing runs, so that might be the only fault. Pretty soon, I discovered 22uF SMD TANTALUM cap that read 5 ohms resistance. It was the input filter for a +12V regulator IC. Got it off the daughter board pronto and fitted a regular electro in place, mounted close to the tiny transformer. It then ran fine and all the low voltage DC rails came up.

The main SMPS will not run unless a control voltage from the amp module is present and the manual gives a clue how to circumvent this - the LED in an opto needs to be energised. So, very gingerly I applied the probes of my old Fluke series 2, in diode test mode, to the relevant pins.

Blow me down, the whole shebang came to life and I had four high power DC rails. A couple of hours more work and I had all the modules back in the case and wired up. Initially the dead channel still refused to start - bugger!
Then I spotted an obvious error with the AC supply to another auxiliary
SMPS on the amp module. Fixed that and it came up.

Next, I performed a series of power output tests to both channels, using steady sine waves and bursts of 4 or 8 on and 16 off with a 4 ohm dummy load. This confirmed QSC\'s rated output of 3.4kW per channel with 4 ohm loads. I did not try 2 ohms, where QSC rate the output as 4.5kW per channel but expect it would have passed.

My customer uses the PL-9 to drive six, horn loaded bass bins in his PA system, each with a 600W, 15inch, 8ohm speakers.

The PL-9 and PL-6 have a reputation for poor reliability, so I hope I never sees this beast again and if it ever blows up it can stay that way, as far as I am concerned.


... Phil
Hi,

Much appreciated post.

Does anyone know how I can privately get in touch with Phil?

Regards
 
W

Wilson F.

Guest
Hello
I would like to help owners of DMR-ES20 to fix the known \"zero\" error.
This occur due a failure on PSU section that can\'t provide correct voltages to other sections/modules.
Is recommended replace 7 electrolytic capacitors (a cap kit) with 105°C range.

C1143 100uF 350V
C1150 56uF 35V
C1280 680uF 10V
C1400 470uf 16V
C1270 1000uf 16V
C1260 1500uF 10V
C1281 47uF 25V
 
A

amdx

Guest
On 8/29/2020 1:29 PM, jo shua wrote:
On Wednesday, 4 March 2015 at 02:30:16 UTC, palli...(edited) wrote:
Hi,

recently, a regular customer brought in his QSC PL-9, a \"9kW\" beast of an amp.

The model was first released nearly 20 years ago, as the flagship of the PowerLight range. My customer\'s example sat in its box until about two years ago when he purchased it and had it shipped to Sydney from the USA.

The model is no longer sold or supported by QSC and was never sold here. Its smaller brother (the PL-6 ) was sold here but is now similarly orphaned.

I agreed to have a look and found that one channel had simply stopped with no signs of serious damage - ie no blown fuses.

The amp consists of four, large modules - two PSUs and two amplifiers stacked on top of each other in pairs and crammed into a 3RU steel box. Access is just terrible and one needs the service manual just to find out how to get the modules out.

Eventually I did and still found no signs of damage, no power devices were shorted or tracks blown and it all looked fine. Next, I transferred the amp module from the dead channel onto the PSU of the working one and it ran just fine. So, it had to be a faulty PSU module.

The PL-9 has the weirdest circuitry I have ever seen, the SMPS is massive and claimed to be PFC but there is no PFC stage involved. What QSC did was to modulate drive to the power switching stage in proportion to the AC voltage at any moment, smoothing out the current draw but without the ability to regulate the resulting DC voltages. It works well enough, as I could see from the good channel. The SMPS produces four DC voltages: 50,100,150 and 200 volts all positive. Max current on the 200V rail is 25amps !!!

Each amplifier is a bridge mode pair with one output grounded - not so unusual until you realise the DC supply jumps in three steps from +50V to +200V in line with the audio signal. QSC have included an elaborate scheme to correct the anomalies this generates and it appears to work.

My customer tried to source a new PSU module here and was told the last selling price was $2500 - but with none available. He might however take advantage of QSC\'s cash rebate deal. Anyone who buys a new PL380 from an authorised dealer is entitled to an US$800 rebate from QSC, if they return a PL-9 or PL-6 to the factory. No requirement that it be in working order is mentioned.

The PL380 is rated at 8kW and is of conventional class D design with no PFC in the SMPS. It is built on a single PCB and amazingly there are only *six* active power devices in the whole amp, compared to several dozen in the PL-9.

Anyhow, I persisted with the faulty PSU a bit longer, running it on the bench on its own from my iso tranny. It did not start up but I could tell an auxiliary switching PSU was pulsing, trying to start up. Making a one turn loop with the ground clip linked to the tip of a scope probe and dropping it over the tiny transformer I saw bursts of HF every 120mS or so. This auxiliary PSU develops a series of low DC voltages to run the daughter board on the main SMPS, +5, +/-15 etc.

If it does not run - nothing runs, so that might be the only fault. Pretty soon, I discovered 22uF SMD TANTALUM cap that read 5 ohms resistance. It was the input filter for a +12V regulator IC. Got it off the daughter board pronto and fitted a regular electro in place, mounted close to the tiny transformer. It then ran fine and all the low voltage DC rails came up.

The main SMPS will not run unless a control voltage from the amp module is present and the manual gives a clue how to circumvent this - the LED in an opto needs to be energised. So, very gingerly I applied the probes of my old Fluke series 2, in diode test mode, to the relevant pins.

Blow me down, the whole shebang came to life and I had four high power DC rails. A couple of hours more work and I had all the modules back in the case and wired up. Initially the dead channel still refused to start - bugger!
Then I spotted an obvious error with the AC supply to another auxiliary
SMPS on the amp module. Fixed that and it came up.

Next, I performed a series of power output tests to both channels, using steady sine waves and bursts of 4 or 8 on and 16 off with a 4 ohm dummy load. This confirmed QSC\'s rated output of 3.4kW per channel with 4 ohm loads. I did not try 2 ohms, where QSC rate the output as 4.5kW per channel but expect it would have passed.

My customer uses the PL-9 to drive six, horn loaded bass bins in his PA system, each with a 600W, 15inch, 8ohm speakers.

The PL-9 and PL-6 have a reputation for poor reliability, so I hope I never sees this beast again and if it ever blows up it can stay that way, as far as I am concerned.


... Phil
Hi,

Much appreciated post.

Does anyone know how I can privately get in touch with Phil?

Regards
Have you tried, Phil Allison <pallison49@gmail.com> ?


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
 
P

Phil Allison

Guest
amdx wrote:

===========
... Phil
Hi,

Much appreciated post.

Does anyone know how I can privately get in touch with Phil?

Regards

Have you tried, Phil Allison <pallison49@gmail.com> ?
** Phil is right here if the OP wants to ask something.



...... Phil
 
K

Ken Layton

Guest
John:

Were those schematics helpful to you? Did you figure out your problem? It\'s been a while so I thought I would ask for a followup.
 
W

William Muff

Guest
On Thursday, March 2, 2000 at 3:00:00 AM UTC-5, Al, N2NKB wrote:
Nice story. Hats off to Paul from Bose.
Al
FarberBear wrote in message <20000302142637...@ng-de1.aol.com>...
Update on this repair:
I decided to try the Bose website for a contact number. They have an 800 number
listed so I tried that. The first time I called Bose customer service, I was on
hold for an hour and then got cut off. The second time I called, I was only on
hold for 30 minutes. Finally, a Bose customer service rep answered. In order to
talk to someone who actually knows the insides of this amp, you have to
persuade the customer service rep to let you talk to a techncian even though
you are not an authorized Bose dealer and don\'t have a schematic. I pleaded
with the customer service rep to just give me 5 minutes with a tech to ask my
question. He connected me to a tech\'s voice mail. Honestly, I didn\'t think I
would get a call back. When a tech did call me back the following day, he was
extremely helpful. He walked me through the troubleshooting steps. In about 15
minutes, we pinpointed the problem to a leaky smd transistor which is
responsible for switching the optocoulpler which in turn, controls the power
on/off via a triac.The reason the problem only occurred in cd mode had
something to do with the load on the 10V control line. When the unit is powered
up, 10 volts is applied to the power amp to electronically switch it on. Of
course the cd player put more load on this 10 volt supply than the tuner did
but I guess it was enough of a difference that the already leaking transistor
couldn\'t do its job. Once the transistor was replaced, the set worked like a
charm.

I tip my hat to Paul Bedard of Bose Corp. who took the time to help me solve
this crazy problem. He then *called* me back later in the day to see if his
advice solved the problem. I hope the other manufacturers are taking notes here
on how to administer good service relations with small independent shops.
Do you happen to have any info on the amperage of the 10v line? I\'m trying to mimic it to turn on an sa3 amp with no bose reciever.
 
D

David Farber

Guest
On 9/8/2020 5:04 PM, William Muff wrote:
On Thursday, March 2, 2000 at 3:00:00 AM UTC-5, Al, N2NKB wrote:
Nice story. Hats off to Paul from Bose.
Al
FarberBear wrote in message <20000302142637...@ng-de1.aol.com>...
Update on this repair:
I decided to try the Bose website for a contact number. They have an 800 number
listed so I tried that. The first time I called Bose customer service, I was on
hold for an hour and then got cut off. The second time I called, I was only on
hold for 30 minutes. Finally, a Bose customer service rep answered. In order to
talk to someone who actually knows the insides of this amp, you have to
persuade the customer service rep to let you talk to a techncian even though
you are not an authorized Bose dealer and don\'t have a schematic. I pleaded
with the customer service rep to just give me 5 minutes with a tech to ask my
question. He connected me to a tech\'s voice mail. Honestly, I didn\'t think I
would get a call back. When a tech did call me back the following day, he was
extremely helpful. He walked me through the troubleshooting steps. In about 15
minutes, we pinpointed the problem to a leaky smd transistor which is
responsible for switching the optocoulpler which in turn, controls the power
on/off via a triac.The reason the problem only occurred in cd mode had
something to do with the load on the 10V control line. When the unit is powered
up, 10 volts is applied to the power amp to electronically switch it on. Of
course the cd player put more load on this 10 volt supply than the tuner did
but I guess it was enough of a difference that the already leaking transistor
couldn\'t do its job. Once the transistor was replaced, the set worked like a
charm.

I tip my hat to Paul Bedard of Bose Corp. who took the time to help me solve
this crazy problem. He then *called* me back later in the day to see if his
advice solved the problem. I hope the other manufacturers are taking notes here
on how to administer good service relations with small independent shops.
Do you happen to have any info on the amperage of the 10v line? I\'m trying to mimic it to turn on an sa3 amp with no bose reciever.

Hi William,
As this interaction happened over 20 years ago, I only have a vague
recollection of this repair. Unfortunately, I am unable to answer your
question about the amperage of the 10v line.

Good luck.
--
David Farber
Los Osos, CA
 
D

David Farber

Guest
On 9/8/2020 5:04 PM, William Muff wrote:
On Thursday, March 2, 2000 at 3:00:00 AM UTC-5, Al, N2NKB wrote:
Nice story. Hats off to Paul from Bose.
Al
FarberBear wrote in message <20000302142637...@ng-de1.aol.com>...
Update on this repair:
I decided to try the Bose website for a contact number. They have an 800 number
listed so I tried that. The first time I called Bose customer service, I was on
hold for an hour and then got cut off. The second time I called, I was only on
hold for 30 minutes. Finally, a Bose customer service rep answered. In order to
talk to someone who actually knows the insides of this amp, you have to
persuade the customer service rep to let you talk to a techncian even though
you are not an authorized Bose dealer and don\'t have a schematic. I pleaded
with the customer service rep to just give me 5 minutes with a tech to ask my
question. He connected me to a tech\'s voice mail. Honestly, I didn\'t think I
would get a call back. When a tech did call me back the following day, he was
extremely helpful. He walked me through the troubleshooting steps. In about 15
minutes, we pinpointed the problem to a leaky smd transistor which is
responsible for switching the optocoulpler which in turn, controls the power
on/off via a triac.The reason the problem only occurred in cd mode had
something to do with the load on the 10V control line. When the unit is powered
up, 10 volts is applied to the power amp to electronically switch it on. Of
course the cd player put more load on this 10 volt supply than the tuner did
but I guess it was enough of a difference that the already leaking transistor
couldn\'t do its job. Once the transistor was replaced, the set worked like a
charm.

I tip my hat to Paul Bedard of Bose Corp. who took the time to help me solve
this crazy problem. He then *called* me back later in the day to see if his
advice solved the problem. I hope the other manufacturers are taking notes here
on how to administer good service relations with small independent shops.
Do you happen to have any info on the amperage of the 10v line? I\'m trying to mimic it to turn on an sa3 amp with no bose reciever.

Hi William,
As this interaction happened over 20 years ago, I only have a vague
recollection of this repair. Unfortunately, I am unable to answer your
question about the amperage of the 10v line.

Good luck.
--
David Farber
Los Osos, CA
 
S

server

Guest
On Tuesday, August 25, 2020 at 11:32:47 PM UTC-7, micky wrote:
In alt.home.repair, on Tue, 25 Aug 2020 11:20:58 -0500, Mark Lloyd
not@mail.invalid> wrote:

On 8/25/20 9:15 AM, micky wrote:

[snip]

OTOH we had to rescan about a month ago and that was the first time in
more than 2 years. More than 5 years?

We had to rescan earlier this year, just because of a new subchannel
(56-4, AntennaTV) that the local NBC station added.

So does that mean if you hadn\'t rescanned, you\'d still have gotten all
the channels but that one.

Could you have just punched in 56,4 and the tv would find it, and then
ou could add it to the internal list, but they said to rescan because
that\'s a simple instruction and applies to everyone, whereas the
instructions for adding a station vary by tv.

[snip]
After the FCC repack in LA several channels moved frequencies so that needed a rescan. KCAL channel 9 has added
3 subchannels but not at the same time so you would need a rescan for each addition. We had an old Magnavox
where you could select the RF channel and a few seconds later it would identify the PSIP and report the
channel. It gets more interesting in that the channel 28 carrier for KCET also has KLCS (ch 58) as subchannels
but behaves as if ch 58 is its own carrier. Likewise channel 50 KOCE is now
subchannels on KSCI ch 18. It did
take them quite a while before they got is sorted so that my TVs and computers would recognize it properly.

G²
 
G

gregz

Guest
<stratus46@yahoo.com> wrote:
On Tuesday, August 25, 2020 at 11:32:47 PM UTC-7, micky wrote:
In alt.home.repair, on Tue, 25 Aug 2020 11:20:58 -0500, Mark Lloyd
not@mail.invalid> wrote:

On 8/25/20 9:15 AM, micky wrote:

[snip]

OTOH we had to rescan about a month ago and that was the first time in
more than 2 years. More than 5 years?

We had to rescan earlier this year, just because of a new subchannel
(56-4, AntennaTV) that the local NBC station added.

So does that mean if you hadn\'t rescanned, you\'d still have gotten all
the channels but that one.

Could you have just punched in 56,4 and the tv would find it, and then
ou could add it to the internal list, but they said to rescan because
that\'s a simple instruction and applies to everyone, whereas the
instructions for adding a station vary by tv.

[snip]

After the FCC repack in LA several channels moved frequencies so that
needed a rescan. KCAL channel 9 has added
3 subchannels but not at the same time so you would need a rescan for
each addition. We had an old Magnavox
where you could select the RF channel and a few seconds later it would
identify the PSIP and report the
channel. It gets more interesting in that the channel 28 carrier for KCET
also has KLCS (ch 58) as subchannels
but behaves as if ch 58 is its own carrier. Likewise channel 50 KOCE is now
subchannels on KSCI ch 18. It did
take them quite a while before they got is sorted so that my TVs and
computers would recognize it properly.

G²
I realize many TVs have very poor or no programming ability, some with more
utility than others. Most in Pittsburgh wonder where the local channel 13
VHF-H went. They can no longer receive the new 60 mHz ch 4 frequency with
tiny antennas LOL.

Greg
 
R

Ralph Mowery

Guest
In article <1402910627621668581.396219zekor-comcast.net@news.eternal-
september.org>, zekor@comcast.net says...
I realize many TVs have very poor or no programming ability, some with more
utility than others. Most in Pittsburgh wonder where the local channel 13
VHF-H went. They can no longer receive the new 60 mHz ch 4 frequency with
tiny antennas LOL.
With so many on cable or other means of getting TV signals other than
off the air, I bet the TV companies spend little time worring about the
tuner part for the antennas.
 
C

crazy chicken

Guest
I am having the exact same problem. What is broken, the VCR or VHS that is making it B&W. Is everything B&W because my VHS tapes are too old and have eroded? I have tapes since 1990, so do they still work 30 years later? Is there no solution to this problem? I am trying to get my tapes to digital, and I need to solve this problem.
Thanks for reading!
- A Chicken
 
D

Dave Platt

Guest
In article <0e80f69b-170d-4252-9982-7405105d3484n@googlegroups.com>,
crazy chicken <craziestchicken2007@gmail.com> wrote:
I am having the exact same problem. What is broken, the VCR or VHS that is making it B&W. Is everything B&W
because my VHS tapes are too old and have eroded? I have tapes since 1990, so do they still work 30 years
later? Is there no solution to this problem? I am trying to get my tapes to digital, and I need to solve this
problem.
https://www.broadcaststore.com/pdf/model/793700/TT198%20-%204802.pdf
has some useful information about how VHS color recording works,
although the details of the testing procedure it suggests won\'t help
you all that much.

With tapes in good condition, and a VCR in good condition and
alignment, color playback should work OK. It\'s unlikely that several
different tapes would have degraded in the same way, so the fault is
more probably with the VCR.

VHS can lose color because of dirty or bad playback heads in the drum,
or because of a fault in the color-conversion circuits (VHS stores the
color information in a different frequency band than is used by NTSC
video). A failed 3.68 MHz color-reference oscillator would be one
such possible fault, and I\'m sure there are plenty of others.

Sure, there\'s a solution: try a different VCR, preferably one which is
in known-good condition.

Your existing VCR might be repairable; it might need something as
simple as a good professional cleaning (and I don\'t mean a \"cleaning
tape\", I mean a by-hand cleaning by a technician who knows how to do
it properly and who won\'t damage the heads) or it might need circuitry
repairs. Old VHS players are common enough that simply buying a
(used) replacement is likely to be cheaper than a repair.

Another possibility - if you have hooked your VCR up to a TV/monitor
using an S-video cable, try a different cable. S-Video sends the
luminance (brightness) signal on one wire, and the chroma (color)
signal on another wire. A broken wire or pin could cut off the chroma
and leave you seeing black-and-white. See if the problem is still
there if you use a composite-video cable (RCA plug/jack, usually
yellow) rather than S-Video.

If you\'re trying to video-capture onto a PC, you might have a problem
with your video-capture card.
 
G

Guy Patterson

Guest
On Friday, September 25, 2020 at 10:02:18 PM UTC-4, crazy chicken wrote:
I am having the exact same problem. What is broken, the VCR or VHS that is making it B&W. Is everything B&W because my VHS tapes are too old and have eroded? I have tapes since 1990, so do they still work 30 years later? Is there no solution to this problem? I am trying to get my tapes to digital, and I need to solve this problem.
Thanks for reading!
- A Chicken
A specific model number would be helpful. I may still have service records somewhere on VCRs. But no, the age of the tape has nothing to do with a loss of chroma in playback assuming the signal to noise ratio is still respectable (viewable image without severe noise). The chroma sub carrier won\'t degrade any faster than any other part of the composite waveform will.

Old VCRs suffer the same issues as modern garbage does: lazy electrolytic caps as they age. If you only need this to run long enough to do a digital transfer, try taking the cover off the VCR and heating the innards for about 10 minutes with a hair dryer (don\'t use a real heat gun). With a good hot soak, a weak electro cap can increase it\'s value and lower it\'s ESR enough to allow the color to work as it should. If it responds to heat, make all your transfers while it stays hot.
 
C

crazy chicken

Guest
Thank you so much! I will tell you if any of this works! If it does, anyone else that comes into the google group will see your message and leave!
 
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