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

[David Farber]

This Carvin B2000 bass amplifier was brought to me with the problem that
it wouldn\'t turn on. The user said it was working fine until there was a
bright flash that could be seen through the front grill. Then it went
dead. I opened it up and found a very fried and crispy looking disc
which I think is an MOV. It\'s labeled TR1 on the \"main board close up\"
as seen in these pictures. You can see by the photo it parallels the
(removed) relay\'s normally open contact (AC out?) and the common, AC in
contact.
Photos are here, https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

The other photos are to give you a general idea of what the board looks
like. The reason I took photos of the entire board is that Carvin\'s own
website, https://carvinaudio.com/pages/bass-amp-schematics shows
different versions of the B2000 schematic but none of them matches what
I see in the version I\'m trying to troubleshoot. There is one vacuum
tube in the unit, a 12AX7.

After cutting out the MOV, and then powering it up, the power relays
would not engage. The other issue is that when I pulled out one of the
two power relays for inspection of its discolored contacts after it
failed to power up, one of the pins came out of its coil. There is no
writing on the relay and its physical construction doesn\'t look at all
familiar to any relays I\'ve ever seen. I need to replace it assuming the
unit is worth fixing.

Does anyone have a schematic for this amp? There is a description of the
amp here:
https://carvinaudio.com/pages/archive-carvin-b2000-lightweight-mono-block-2050w-bass-amp-head

The owner said it was purchased around 2000. It looks in good shape for
being 20 years old. According to this report,
https://www.thetonerooms.com/threads/carvin-amps-out-of-business.3035/
Carvin went of business in 2017.

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

 

[Phil Allison]

David Farber wrote:

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

This Carvin B2000 bass amplifier was brought to me with the problem that
it wouldn\'t turn on. The user said it was working fine until there was a
bright flash that could be seen through the front grill. Then it went
dead. I opened it up and found a very fried and crispy looking disc
which I think is an MOV. It\'s labeled TR1 on the \"main board close up\"
as seen in these pictures. You can see by the photo it parallels the
(removed) relay\'s normally open contact (AC out?) and the common, AC in
contact.
Photos are here, https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

The other photos are to give you a general idea of what the board looks
like. The reason I took photos of the entire board is that Carvin\'s own
website, https://carvinaudio.com/pages/bass-amp-schematics shows
different versions of the B2000 schematic but none of them matches what
I see in the version I\'m trying to troubleshoot. There is one vacuum
tube in the unit, a 12AX7.

After cutting out the MOV, and then powering it up, the power relays
would not engage. The other issue is that when I pulled out one of the
two power relays for inspection of its discolored contacts after it
failed to power up, one of the pins came out of its coil. There is no
writing on the relay and its physical construction doesn\'t look at all
familiar to any relays I\'ve ever seen. I need to replace it assuming the
unit is worth fixing.

Does anyone have a schematic for this amp? There is a description of the
amp here:
https://carvinaudio.com/pages/archive-carvin-b2000-lightweight-mono-block-2050w-bass-amp-head

The owner said it was purchased around 2000. It looks in good shape for
being 20 years old. According to this report,
https://www.thetonerooms.com/threads/carvin-amps-out-of-business.3035/
Carvin went of business in 2017.

** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.


..... Phil

 

[David Farber]

On 9/20/2020 8:06 PM, Phil Allison wrote:

David Farber wrote:

===================
This Carvin B2000 bass amplifier was brought to me with the problem that
it wouldn\'t turn on. The user said it was working fine until there was a
bright flash that could be seen through the front grill. Then it went
dead. I opened it up and found a very fried and crispy looking disc
which I think is an MOV. It\'s labeled TR1 on the \"main board close up\"
as seen in these pictures. You can see by the photo it parallels the
(removed) relay\'s normally open contact (AC out?) and the common, AC in
contact.
Photos are here, https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

The other photos are to give you a general idea of what the board looks
like. The reason I took photos of the entire board is that Carvin\'s own
website, https://carvinaudio.com/pages/bass-amp-schematics shows
different versions of the B2000 schematic but none of them matches what
I see in the version I\'m trying to troubleshoot. There is one vacuum
tube in the unit, a 12AX7.

After cutting out the MOV, and then powering it up, the power relays
would not engage. The other issue is that when I pulled out one of the
two power relays for inspection of its discolored contacts after it
failed to power up, one of the pins came out of its coil. There is no
writing on the relay and its physical construction doesn\'t look at all
familiar to any relays I\'ve ever seen. I need to replace it assuming the
unit is worth fixing.

Does anyone have a schematic for this amp? There is a description of the
amp here:
https://carvinaudio.com/pages/archive-carvin-b2000-lightweight-mono-block-2050w-bass-amp-head

The owner said it was purchased around 2000. It looks in good shape for
being 20 years old. According to this report,
https://www.thetonerooms.com/threads/carvin-amps-out-of-business.3035/
Carvin went of business in 2017.



** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.


.... Phil

Hi Phil. I think I\'ll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I\'ll also put a 200 watt light bulb in series
with the Variac just in case. If there\'s no overload, then I may as well
pull out the other identical inrush relay and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?

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

 

[Phil Allison]

David Farber wrote:

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

** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.




Hi Phil. I think I\'ll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I\'ll also put a 200 watt light bulb in series
with the Variac just in case.

** That\'s fine.

If there\'s no overload, then I may as well
pull out the other identical inrush relay

* Are there 2 PSUs involved?

and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?

** 20A at 120VAC at least.


..... Phil

 

[legg]

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

On 9/20/2020 8:06 PM, Phil Allison wrote:
David Farber wrote:

===================
This Carvin B2000 bass amplifier was brought to me with the problem that
it wouldn\'t turn on. The user said it was working fine until there was a
bright flash that could be seen through the front grill. Then it went
dead. I opened it up and found a very fried and crispy looking disc
which I think is an MOV. It\'s labeled TR1 on the \"main board close up\"
as seen in these pictures. You can see by the photo it parallels the
(removed) relay\'s normally open contact (AC out?) and the common, AC in
contact.
Photos are here, https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

The other photos are to give you a general idea of what the board looks
like. The reason I took photos of the entire board is that Carvin\'s own
website, https://carvinaudio.com/pages/bass-amp-schematics shows
different versions of the B2000 schematic but none of them matches what
I see in the version I\'m trying to troubleshoot. There is one vacuum
tube in the unit, a 12AX7.

After cutting out the MOV, and then powering it up, the power relays
would not engage. The other issue is that when I pulled out one of the
two power relays for inspection of its discolored contacts after it
failed to power up, one of the pins came out of its coil. There is no
writing on the relay and its physical construction doesn\'t look at all
familiar to any relays I\'ve ever seen. I need to replace it assuming the
unit is worth fixing.

Does anyone have a schematic for this amp? There is a description of the
amp here:
https://carvinaudio.com/pages/archive-carvin-b2000-lightweight-mono-block-2050w-bass-amp-head

The owner said it was purchased around 2000. It looks in good shape for
being 20 years old. According to this report,
https://www.thetonerooms.com/threads/carvin-amps-out-of-business.3035/
Carvin went of business in 2017.



** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.


.... Phil


Hi Phil. I think I\'ll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I\'ll also put a 200 watt light bulb in series
with the Variac just in case. If there\'s no overload, then I may as well
pull out the other identical inrush relay and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?

It\'s a fairly common form used in HVAC switching, but more easily
obtained with a plastic dust cap. The open air parts are seldom
used outside of self enclosed fan-free environments, for obvious
reasons.

You may have a relay on both input (inrush limiting) and output
(click and pop supression).

You\'ll need to establish what the supply voltage is for the coils.

Check for Panasonic JTV or TEconnect T9AS1D series SPST NO.

RL

 

[legg]

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.

RL

 

[legg]

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

 

[David Farber]

On 9/20/2020 10:40 PM, Phil Allison wrote:

David Farber wrote:

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



** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.




Hi Phil. I think I\'ll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I\'ll also put a 200 watt light bulb in series
with the Variac just in case.

** That\'s fine.

If there\'s no overload, then I may as well
pull out the other identical inrush relay

* Are there 2 PSUs involved?


and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?


** 20A at 120VAC at least.


.... Phil

Hi Phil,

I\'ve found what I think is a partial schematic for this model which I\'ve
added to my Carvin folder here:
https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

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

 

[David Farber]

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.
--
David Farber
Los Osos, CA

 

[legg]

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.

Unfortunately, this doesn\'t cover the power section.

RL

 

[legg]

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

 

[Phil Allison]

Phil Allison wrote:

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

The blown device is a PTC thermistor


** Of course that should be an * NTC thermistor*.

https://passive-components.eu/how-to-use-ntc-thermistors-for-inrush-current-limiting/


...... Phil

 

[David Farber]

On 9/21/2020 3:57 PM, Phil Allison wrote:

Phil Allison wrote:

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



The blown device is a PTC thermistor


** Of course that should be an * NTC thermistor*.

https://passive-components.eu/how-to-use-ntc-thermistors-for-inrush-current-limiting/


..... Phil

I found this NTC-5D11 on eBay.
https://www.ebay.com/itm/141513042814
The datasheet says it\'s 5 ohms, continuous current 4 amps, and 0.0156
ohms at max current.

I still need to check the circuit first to make sure there is no overload.

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

 

[David Farber]

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

 

[Phil Allison]

David Farber wrote:

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

** Of course that should be an * NTC thermistor*.

https://passive-components.eu/how-to-use-ntc-thermistors-for-inrush-current-limiting/


I found this NTC-5D11 on eBay.
https://www.ebay.com/itm/141513042814
The datasheet says it\'s 5 ohms, continuous current 4 amps, and 0.0156
ohms at max current.

** Way to much to pay for shipping.

Newark has the same for 50 cents each.

I still need to check the circuit first to make sure there is no overload.

** The original NTC may be way higher in value than 5 ohms - up to 50 ohms maybe.

I gave that number for tests using a Variac only.


..... Phil

 

[David Farber]

On 9/20/2020 10:40 PM, Phil Allison wrote:

David Farber wrote:

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



** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.




Hi Phil. I think I\'ll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I\'ll also put a 200 watt light bulb in series
with the Variac just in case.

** That\'s fine.

If there\'s no overload, then I may as well
pull out the other identical inrush relay

* Are there 2 PSUs involved?


and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?


** 20A at 120VAC at least.


.... Phil

Before I went to the trouble of dismantling my audio dummy load resistor
setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and
soldered them in place of the thermistor. (My supply of resistors in the
low ohm, high power range is almost nil.) I know you said to use at
least a 5 watt resistor but I wanted to get some idea of what kind of
current the amp would draw on power up. I did put a 200 watt lamp in
series. By the time the line voltage was up to 50 ACV, the lamp was
glowing at about half strength and the AC current was about 1 amp. The
voltage across the resistors was over 3 volts so they were already
overloading. At that point I aborted the test. If I do repeat this test
with the 8 ohm, audio, 25 watt dummy load resistor, should I leave the
light bulb in series? Would it take more than 2 amps of continuous AC
power even when bringing up the voltage slowly? What if I bypass the
relay contacts and eliminate the resistors? There shouldn\'t be any
inrush surge while bringing the voltage up slowly, right?

I should also mention that the power amp has a 25 amp line fuse inside.
Does that sound reasonable? Neither the schematic nor the PC board
indicate what the fuse rating should be.

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

 

[Phil Allison]

David Farber wrote
==================:

Before I went to the trouble of dismantling my audio dummy load resistor
setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and
soldered them in place of the thermistor. (My supply of resistors in the
low ohm, high power range is almost nil.) I know you said to use at
least a 5 watt resistor but I wanted to get some idea of what kind of
current the amp would draw on power up. I did put a 200 watt lamp in
series.

** Completely spoils the test.

By the time the line voltage was up to 50 ACV, the lamp was
glowing at about half strength and the AC current was about 1 amp.

** So nearly 50V AC was across the 200W lamp.

Odds are very high the PSU is a dead short to the AC supply - though the bridge rectifier may be OK. Check that and some FETs with a multimeter on diode tests.



..... Phil

 

[David Farber]

On 9/24/2020 8:18 PM, Phil Allison wrote:

David Farber wrote
==================:

Before I went to the trouble of dismantling my audio dummy load resistor
setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and
soldered them in place of the thermistor. (My supply of resistors in the
low ohm, high power range is almost nil.) I know you said to use at
least a 5 watt resistor but I wanted to get some idea of what kind of
current the amp would draw on power up. I did put a 200 watt lamp in
series.

** Completely spoils the test.


By the time the line voltage was up to 50 ACV, the lamp was
glowing at about half strength and the AC current was about 1 amp.

** So nearly 50V AC was across the 200W lamp.

Odds are very high the PSU is a dead short to the AC supply - though the bridge rectifier may be OK. Check that and some FETs with a multimeter on diode tests.



.... Phil


I will recheck for shorts in the PSU.

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

 

[David Farber]

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.

I still have one issue that needs resolving. I performed an in circuit
diode test across D809 and D810. They both read 105 ohms (regardless of
the polarity of the probes). In essence, connecting either one of those
diode\'s terminal with one probe and then connecting the other to ground
yields that same 105 ohm reading. On the other side of that bridge diode
circuit, D811 and D812 yield normal front to back in circuit diode
readings. Desoldering any of the components is quite a chore because of
the double-layered board. I am stumped trying to figure out the
troubleshooting path of least resistance here. I haven\'t ruled out that
the 105 ohm reading may just be normal but my gut feeling says it\'s not.

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

 

[legg]

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

<snip>

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.

I still have one issue that needs resolving. I performed an in circuit
diode test across D809 and D810. They both read 105 ohms (regardless of
the polarity of the probes). In essence, connecting either one of those
diode\'s terminal with one probe and then connecting the other to ground
yields that same 105 ohm reading. On the other side of that bridge diode
circuit, D811 and D812 yield normal front to back in circuit diode
readings. Desoldering any of the components is quite a chore because of
the double-layered board. I am stumped trying to figure out the
troubleshooting path of least resistance here. I haven\'t ruled out that
the 105 ohm reading may just be normal but my gut feeling says it\'s not.

The anodes of D809 and D810 are DC-shorted through the transformer
winding. The 105R reading is likely between LORAIL+ and ground.

RL

RL