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

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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.

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• Are there 2 PSUs involved?

.... Phil

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

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

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

Hi Phil,

I've found what I think is a partial schematic for this model which I've added to my Carvin folder here:

Thanks for your reply.

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:

Thanks for your reply.

Unfortunately, this doesn't cover the power section.

RL

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

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:

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

RL

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..... Phil

I found this NTC-5D11 on eBay.

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

Thanks for your reply.

That's a great find. I wonder if the schematic I found earlier in my research,

Thanks for your reply.

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Newark has the same for 50 cents each.

I gave that number for tests using a Variac only.

.... 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 wrote ==================:

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.

Schematic is here:

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.

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

RL

RL