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Carvin B2000 bass amp won\'t power on, need schematic....

L

legg

Guest
On Thu, 1 Oct 2020 15:21:36 -0700, David Farber
<farberbear.unspam@aol.com> wrote:

On 9/21/2020 8:55 PM, David Farber wrote:
On 9/21/2020 12:00 PM, legg wrote:
On Mon, 21 Sep 2020 09:57:39 -0700, David Farber
farberbear.unspam@aol.com> wrote:

On 9/21/2020 8:34 AM, legg wrote:
On Mon, 21 Sep 2020 09:59:22 -0400, legg <legg@nospam.magma.ca> wrote:

On Sun, 20 Sep 2020 22:17:29 -0700, David Farber
farberbear.unspam@aol.com> wrote:

Actuslly, the second relay looks more like a line voltage
selector. It will close for line voltages below 180VAC.

It looks like this unit isn\'t power factor corrected.


If that\'s the case, then you could do a quick fix by
relocating the voltage select relay to the inrush
position, short out the old voltage select relay
contact position, then place a large sticker on
the back indicating \"100-130VAC INPUT ONLY\".

RL

What an ingenious workaround! I\'ll definitely check out that relay swap
option.

By the way, the user informed me the model was not purchased in 2000. It
was purchased in 2009. There is a schematic for that year but it looks
incomplete to me. I\'ve uploaded it to:
https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

Thanks for your reply.

The following schematic covers models:
DCM1540L
DCM2000L
DCM3000L
DCM3800L
B2000 Rev J

https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

It has a line input and power stage looks similar to the
one you\'re fooling with, but I don\'t see a tube section
inserted anywhere.

You can wade through other Carvin docs:

https://carvinaudio.com/pages/power-amplifier-schematic

The older B2000 had a 60Hz transformer power supply, unlike
your unit.

RL

That\'s a great find. I wonder if the schematic I found earlier in my
research,
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161
interconnects with this new one you found.

Thanks for your reply.
--
David Farber
Los Osos, CA

Schematic is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

I finally was able to figure out where all the power supply components
were hiding. They were obscured by the heat sinks. The culprits were
Q800 and Q802. Their part numbers are STGW30NC60W and they were both
shorted across all three terminals.
Check the gate components, if the fets fail. They don\'t always
survive.

The primary housekeeper around Q803 should run independently, with big
fets out of circuit, so you can check basic control and drive circuits
without a lot of risk (taking in mind it\'s still a primary-connected
circuit.

RL
 
P

Phil Allison

Guest
David Farber wrote:

------------------
.
Schematic is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

I finally was able to figure out where all the power supply components
were hiding. They were obscured by the heat sinks. The culprits were
Q800 and Q802. Their part numbers are STGW30NC60W and they were both
shorted across all three terminals.
** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.



...... Phil
 
D

David Farber

Guest
On 10/1/2020 11:51 PM, Phil Allison wrote:
David Farber wrote:

------------------
.
Schematic is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

I finally was able to figure out where all the power supply components
were hiding. They were obscured by the heat sinks. The culprits were
Q800 and Q802. Their part numbers are STGW30NC60W and they were both
shorted across all three terminals.


** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.



..... Phil
Thank you Phil and RL. After much poking and prodding trying to reverse
engineer which circuit was going where, the previous 105 ohm low
readings across D809 and D810 are now normal. Maybe a spec of solder
took up residence in the area when I was desoldering the adjacent
transistors, Q800 and Q802?

Next (but still without a new set of IGBT\'s installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT\'s and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I\'ll update you after the new
parts arrive and are installed.

I do have one other question regarding the 25A line fuse. What the heck
is that supposed to protect? If the power supply fails/shorts, the
thermistor bypass relay de-energizes and then the line voltage is sent
through the thermistor. I think the 25A fuse will win that battle and
not protect anything. The specs on the back of the amp say, 2050W into 2
ohms so I guess a large fuse is necessary however wouldn\'t a smaller
fuse, maybe a slo-blo type, make more sense?

One last comment about the schematic. This B2000 model is a mono amp so
anything in the schematic that says CH2, does not exist though about
one-third of the circuit board has empty spots for those components.

Thanks for your replies.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:

------------------

** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.


Next (but still without a new set of IGBT\'s installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT\'s and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I\'ll update you after the new
parts arrive and are installed.
** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.

As you Variac up, the wave should snap on staring with a very low duty cycle, then fill out to a perfectly symmetrical square wave.



I do have one other question regarding the 25A line fuse. What the heck
is that supposed to protect? If the power supply fails/shorts, the
thermistor bypass relay de-energizes and then the line voltage is sent
through the thermistor. I think the 25A fuse will win that battle and
not protect anything. The specs on the back of the amp say, 2050W into 2
ohms so I guess a large fuse is necessary however wouldn\'t a smaller
fuse, maybe a slo-blo type, make more sense?
** At full power with 2ohms load, the AC will be 25amps RMS.

( 2100 /120 = 17.5 with a PF of about 0.7 = 25. )

If you know the speaker being used is 4 or 8 ohms and the player does not thrash the heck out of it - then a 15amp slo-blo will do OK.


..... Phil
 
D

David Farber

Guest
On 10/3/2020 4:33 PM, Phil Allison wrote:
David Farber wrote:

------------------


** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.


Next (but still without a new set of IGBT\'s installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT\'s and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I\'ll update you after the new
parts arrive and are installed.

** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.

As you Variac up, the wave should snap on staring with a very low duty cycle, then fill out to a perfectly symmetrical square wave.



I do have one other question regarding the 25A line fuse. What the heck
is that supposed to protect? If the power supply fails/shorts, the
thermistor bypass relay de-energizes and then the line voltage is sent
through the thermistor. I think the 25A fuse will win that battle and
not protect anything. The specs on the back of the amp say, 2050W into 2
ohms so I guess a large fuse is necessary however wouldn\'t a smaller
fuse, maybe a slo-blo type, make more sense?


** At full power with 2ohms load, the AC will be 25amps RMS.

( 2100 /120 = 17.5 with a PF of about 0.7 = 25. )

If you know the speaker being used is 4 or 8 ohms and the player does not thrash the heck out of it - then a 15amp slo-blo will do OK.


.... Phil
Thanks for the tips. I\'ll check out the drive to each IGBT while
powering it up slowly.

--
David Farber
Los Osos, CA
 
D

David Farber

Guest
On 10/3/2020 4:33 PM, Phil Allison wrote:
David Farber wrote:

------------------


** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.


Next (but still without a new set of IGBT\'s installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT\'s and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I\'ll update you after the new
parts arrive and are installed.

** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.
The parts finally arrived. I\'m a bit confused as to how the schematic of
the IGBT in the datasheet compares to the resistance readings on the
component itself.
http://datasheet.octopart.com/STGW30NC60WD-STMicroelectronics-datasheet-10835944.pdf

Placing the positive probe on pin 2 and the negative probe on pin 3
reads open circuit. If I then put the positive probe on pin 1 and the
negative probe on pin 3 it reads open circuit. Then going back to my
original test of positive on pin 2 and negative on pin 3, I get a
reading of a good diode check around 475 ohms. Subsequently reversing
the probes from pins 1 and 3 and then going back to pins 2 and 3, that
will revert to an open circuit. These readings are what I expect when
testing an FET. According to the datasheet, there is a diode across pins
2 and 3. That would mean if I put positive on pin 3 and negative on pin
2, I should get a good diode check reading but I get an open circuit.
Can you make sense out of these tests?

Thanks for your reply.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:

----------------
The parts finally arrived.
** From where ????



http://datasheet.octopart.com/STGW30NC60WD-STMicroelectronics-datasheet-10835944.pdf
** Shows a a reverse diode HAS been added to the device.

If it is genuine, you should see diode conduction ( 0.8 to 1V) with a DMM set to \"diode check\" range.



..... Phil
 
D

David Farber

Guest
On 10/18/2020 3:27 PM, Phil Allison wrote:
David Farber wrote:

----------------

The parts finally arrived.

** From where ????



http://datasheet.octopart.com/STGW30NC60WD-STMicroelectronics-datasheet-10835944.pdf


** Shows a a reverse diode HAS been added to the device.

If it is genuine, you should see diode conduction ( 0.8 to 1V) with a DMM set to \"diode check\" range.



.... Phil
Parts were from Digi-Key. I took another look at the original, shorted
parts. They are, STGB30NC60WD. I somehow managed to omit the \"D\" at the
end of the part number when I ordered the replacements (and also omitted
it when I reported to the group what the part number was). That would
explain why the reverse diode is absent. I guess it\'s a very good thing
I checked all of this out before powering it up again. I will order the
correct parts and check back with you in a week or so.

By the way, I noticed a potential problem with checking the input
waveforms to the gates of Q800 and Q802. If I put one scope probe across
one transisor, from G to E, that should be OK however if I want to see
both waveforms together while powering up the unit and then connect a
second probe to the scope on the other transistor, the common ground of
the probe will short out Q802. Should I just float the ground on one of
the probes? Will that work? The amp will be powered by my Sencore
isolation transformer/Variac.

Thanks for your reply.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:

====================

By the way, I noticed a potential problem with checking the input
waveforms to the gates of Q800 and Q802. If I put one scope probe across
one transisor, from G to E, that should be OK however if I want to see
both waveforms together while powering up the unit and then connect a
second probe to the scope on the other transistor, the common ground of
the probe will short out Q802. Should I just float the ground on one of
the probes? Will that work?
** Both signals come from the same transformer - out of phase.

You can monitor the outputs of the 3525 IC or the primary side of the tranny without the iso in use.

Plus check continuity of secondary windings and their connections to the IGBTS.

..... Phil
 
D

David Farber

Guest
On 10/18/2020 6:38 PM, Phil Allison wrote:
David Farber wrote:

====================


By the way, I noticed a potential problem with checking the input
waveforms to the gates of Q800 and Q802. If I put one scope probe across
one transisor, from G to E, that should be OK however if I want to see
both waveforms together while powering up the unit and then connect a
second probe to the scope on the other transistor, the common ground of
the probe will short out Q802. Should I just float the ground on one of
the probes? Will that work?



** Both signals come from the same transformer - out of phase.

You can monitor the outputs of the 3525 IC or the primary side of the tranny without the iso in use.

Plus check continuity of secondary windings and their connections to the IGBTS.

.... Phil
Thanks for following up with the details Phil.

--
David Farber
Los Osos, CA
 
D

David Farber

Guest
On 10/18/2020 7:32 PM, David Farber wrote:
On 10/18/2020 6:38 PM, Phil Allison wrote:
  David Farber wrote:

===================
By the way, I noticed a potential problem with checking the input
waveforms to the gates of Q800 and Q802. If I put one scope probe across
one transisor, from G to E, that should be OK however if I want to see
both waveforms together while powering up the unit and then connect a
second probe to the scope on the other transistor, the common ground of
the probe will short out Q802. Should I just float the ground on one of
the probes? Will that work?



** Both signals come from the same transformer - out of phase.

You can monitor the outputs of the 3525 IC or the primary side of the
tranny without the iso in use.

Plus check continuity of secondary windings and their connections to
the IGBTS.

....  Phil


Thanks for following up with the details Phil.

--
David Farber
Los Osos, CA
Note: The tests I performed below were without the control board
connected. The control board is responsible for connecting the earth
ground to the audio ground. The schematic of the control board is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161

The schematic of the main board is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161

I received the correct parts and installed them. I checked the waveform
at the primary side of T2. As I powered it up slowly with the Variac,
there was no gradual change in the duty cycle. It was either flat line
or full on. I checked the signal across Q802 from drain to source and it
was a very clean square wave and measured approximately 400 Vpp. At this
point I could reassemble everything and see if it actually will perform
properly. But before I do that, I would like to figure out the operation
of the power supply circuit that is rectified by diodes D805-D808. It\'s
easy to see that when pin 20 of T3 goes positive, D805 conducts and
becomes the V+ line. From that point, it feeds the load and then I
imagine it ends up going through ground via the terminal marked HI RAIL
on T3 and also through the other ground circuit which is in series with
the array of capacitors, C811-812, C849-850, and C34, C36, and C51.
Apparently there is also a connection to the bridge circuit, D809-D812.
Is there some voltage adding going on there with the secondary
transformer windings interacting with the two bridge circuits? This is
not a configuration that I have come across before. At the very least
I\'d like to know where ground is for the V+ supply coming from the
cathodes of D805 and D806. I am measuring 90 volts individually across
capacitors C850 C852.

Thanks for your reply.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:

==================
As I powered it up slowly with the Variac,
there was no gradual change in the duty cycle. It was either flat line
or full on.
** Very bad.

Check the 22uF on pin 8 of the PWM IC.

This cap enables the Soft Start circuitry.

https://www.ti.com/lit/ds/symlink/uc3525a.pdf?ts=1604980536419&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUC3525A

Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


..... Phil
 
D

David Farber

Guest
On 11/9/2020 8:06 PM, Phil Allison wrote:
David Farber wrote:

==================

As I powered it up slowly with the Variac,
there was no gradual change in the duty cycle. It was either flat line
or full on.


** Very bad.

Check the 22uF on pin 8 of the PWM IC.

This cap enables the Soft Start circuitry.

https://www.ti.com/lit/ds/symlink/uc3525a.pdf?ts=1604980536419&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUC3525A

Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


.... Phil
I hadn\'t realized that the ramp up occurred within 1 second. I powered
it on without the Variac and sure enough, the waveform made a gradual
change within that 1 second timeframe. Everything seems to powering up
OK. Checking the audio will be next.

I\'m still curious about the power supply question I asked in my previous
post (see below) regarding how the two bridge diode circuits seem to be
adding voltage in a series circuit.
============================================

At this point I could reassemble everything and see if it actually will
perform properly. But before I do that, I would like to figure out the
operation of the power supply circuit that is rectified by diodes
D805-D808. It\'s easy to see that when pin 20 of T3 goes positive, D805
conducts and becomes the V+ line. From that point, it feeds the load and
then I imagine it ends up going through ground via the terminal marked
HI RAIL on T3 and also through the other ground circuit which is in
series with the array of capacitors, C811-812, C849-850, and C34, C36,
and C51. Apparently there is also a connection to the bridge circuit,
D809-D812. Is there some voltage adding going on there with the
secondary transformer windings interacting with the two bridge circuits?
This is not a configuration that I have come across before. At the very
least I\'d like to know where ground is for the V+ supply coming from the
cathodes of D805 and D806. I am measuring 90 volts individually across
capacitors C850 C852.

Thanks for your reply.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:

=================>
Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


I hadn\'t realized that the ramp up occurred within 1 second. I powered
it on without the Variac and sure enough, the waveform made a gradual
change within that 1 second timeframe. Everything seems to powering up
OK. Checking the audio will be next.
** So far - so good.

I\'m still curious about the power supply question I asked in my previous
post (see below) regarding how the two bridge diode circuits seem to be
adding voltage in a series circuit.
===========================================
** Yep- it sure is complicated !!.

The DC supply is *series stacked* with a low an high voltage components.

Then a pair of IGBTs for each channel is used to *regulate* the voltage to the main BJT amplifiers so it TRACKS the incoming audio. Maybe not perfectly but reasonably close to demand and just a lite more volts than needed by the load at any moment. The low voltage DC supply sets a fixed lower limit.

Look up \"class H\" on Wiki.

I only know of one other amp maker doing this, Lab Gruppen.

Crazy complicated - why not go Class D an keep it simple ??


...... Phil
 
P

Phil Allison

Guest
David Farber wrote:

==================

** FYI Dave,

The marketing for this model (B2000) is totally wrong.

1. It is not a \"mono block\"- it has two distinct power channels that must drive two different speakers.

2. It sure as HELL ain\'t \"class D\" Either.

The PSU tracks so it is \"clearly class H\"

WTF ???



..... Phil
 
D

David Farber

Guest
On 11/10/2020 8:48 PM, Phil Allison wrote:
David Farber wrote:

==================


Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


I hadn\'t realized that the ramp up occurred within 1 second. I powered
it on without the Variac and sure enough, the waveform made a gradual
change within that 1 second timeframe. Everything seems to powering up
OK. Checking the audio will be next.

** So far - so good.


I\'m still curious about the power supply question I asked in my previous
post (see below) regarding how the two bridge diode circuits seem to be
adding voltage in a series circuit.
============================================


** Yep- it sure is complicated !!.

The DC supply is *series stacked* with a low an high voltage components.

Then a pair of IGBTs for each channel is used to *regulate* the voltage to the main BJT amplifiers so it TRACKS the incoming audio. Maybe not perfectly but reasonably close to demand and just a lite more volts than needed by the load at any moment. The low voltage DC supply sets a fixed lower limit.

Look up \"class H\" on Wiki.

I only know of one other amp maker doing this, Lab Gruppen.

Crazy complicated - why not go Class D an keep it simple ??


..... Phil

Hi Phil,
My experience with commercial(?), high powered audio gear with switching
power supplies is almost nil. I\'ll check out class H on Wiki and while
I\'m there, I\'ll check out any other classes that I haven\'t come across.

Yesterday, I installed the PC board into the chassis and connected the
front panel connectors. The result was the earth ground became tied to
the power supply ground which should have made voltage testing much
easier except for the fact that I could no longer access the bottom of
the PC board. It\'s next to impossible to accurately put a probe on
anything from the component side. Many parts are covered in epoxy(?) or
hot glue(?) and the power transistors are totally obscured by the heat
sinks that surround them.

Thanks for your reply.
--
David Farber
Los Osos, CA
 
D

David Farber

Guest
On 11/10/2020 9:22 PM, Phil Allison wrote:
David Farber wrote:

==================

** FYI Dave,

The marketing for this model (B2000) is totally wrong.

1. It is not a \"mono block\"- it has two distinct power channels that must drive two different speakers.

2. It sure as HELL ain\'t \"class D\" Either.

The PSU tracks so it is \"clearly class H\"

WTF ???



.... Phil



Hi Phil,
When I was still trying to figure out if the schematic matched the pc
board, I mentioned in passing that the second channel audio amplifier
components were not installed. There are however marked out spaces for
them. In summary, any components that refer to CH2 do not exist. As to
whether it is class D or class H (I don\'t think my electronics training
from the 1970\'s went past class C), I\'ll leave that up to you and in the
meantime, I\'ll turn to the internet to update my knowledge about the
alphabet soup of amplifier classes.

Thanks for your reply.
--
David Farber
Los Osos, CA
 
P

Phil Allison

Guest
David Farber wrote:
===================
** FYI Dave,

The marketing for this model (B2000) is totally wrong.

1. It is not a \"mono block\"- it has two distinct power channels that must drive two different speakers.

2. It sure as HELL ain\'t \"class D\" Either.

The PSU tracks so it is \"clearly class H\"

WTF ???





Hi Phil,

When I was still trying to figure out if the schematic matched the pc
board, I mentioned in passing that the second channel audio amplifier
components were not installed. There are however marked out spaces for
them. In summary, any components that refer to CH2 do not exist.
** So you posted the wrong schematic.

Bound to be many differences when the PSU only has to power 1 channel instead of 2.


As to
whether it is class D or class H (I don\'t think my electronics training
from the 1970\'s went past class C),
** No, classes G and H are more recent inventions.

If you have not kept up with the literature (ie electronics magazines) since the early 70s you are living in the dark ages. Before the internet ruined everything, I used to buy 4 magazines each month. Only one of them is still published.

Wireless World from the UK was the best, but it folded years ago.


I\'ll leave that up to you and in the
meantime, I\'ll turn to the internet to update my knowledge about the
alphabet soup of amplifier classes.
** Be sure not to confuse the topic with \"alphabet people\".



...... Phil
 
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