David Farber wrote:

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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 he
https://carvinaudio.com/pages/archiv...-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...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