Carvin vt112 low output

[nickb]

On this chip positive input is pin7 and negative input is pin 14 right? Those measurements were chip out. With the chip in should I have the FS plugged in? I can measure chip in in one direction and flip it around and measure another way.

nosaj

No. Pin 14 is +ve and pin 7 is -ve. So, when you put the chip back in make sure you get chip pin 14 on the +ve socket pin.

Leave the footswitch out for now in case it has it's own issues.

[nosaj]

No. Pin 14 is +ve and pin 7 is -ve. So, when you put the chip back in make sure you get chip pin 14 on the +ve socket pin.

Leave the footswitch out for now in case it has it's own issues.

Ok flipped chip around made no difference. So I took voltages at .02 caps 6.54 and -6.54 respectively, had to bend one over a littleso I could see resistors it was covering because I was going to figure out which resistor hooked up where on the cmos. Took voltages again now different i think moving that cap had something to do with it. so I'm gonna retouch solder joints in that area.
Here's voltages I have now with chip in after several tries I verified pinnumbers to ic datasheet. Compared to the order of the other chips it is the only one with pin1 at the bottom. The 4136 are oriented the other way.

Thanks so much for your help. I think we are there or almost there on the cmos. I'm thinking next step is to input 1khz then checking voltage to see what it is amplified to right before power amp. What should volume control be at and the harmonic control?


jason

pin1 0 pin8 4.17
pin2 0 pin9 4.17
pin3 0 pin10 6.44
pin4 0 pin11 6.44
pin5 4.17 pin12 6.44
pin6 4.03 pin13 4.02
pin7 -6.32 pin14 6.44

[nickb]

pin1 0 OK
pin2 0 OK
pin3 0 OK
pin4 0 OK
pin5 4.17 expected 6.4 Maybe Meter loading?
pin6 4.03 expected 6.4 Maybe Meter loading?
pin7 -6.32 OK
pin8 4.17 OK
pin9 4.17 OK
pin10 6.44 OK
pin11 6.44 OK
pin12 6.44 OK
pin13 4.02 expected 6.4 Maybe Meter loading?
pin14 6.44 OK


Looks good

In this state both normal and sustain signal paths are complete. If the signal is still weak then most likely it is something in common i.e. from the equalizer onwards. In any case, turn the sustain vol up full and apply a 100mvpp 1Khz signal to the sustain input. Using your scope report the signal levels (Vpp) on:


U1-10,
U2-12,
the output of the equalizer
U2-10

[nosaj]

pin1 0 OK
pin2 0 OK
pin3 0 OK
pin4 0 OK
pin5 4.17 expected 6.4 Maybe Meter loading?
pin6 4.03 expected 6.4 Maybe Meter loading?
pin7 -6.32 OK
pin8 4.17 OK
pin9 4.17 OK
pin10 6.44 OK
pin11 6.44 OK
pin12 6.44 OK
pin13 4.02 expected 6.4 Maybe Meter loading?
pin14 6.44 OK


Looks good

In this state both normal and sustain signal paths are complete. If the signal is still weak then most likely it is something in common i.e. from the equalizer onwards. In any case, turn the sustain vol up full and apply a 100mvpp 1Khz signal to the sustain input. Using your scope report the signal levels (Vpp) on:


U1-10,
U2-12,
the output of the equalizer
U2-10

Last question before testing. What about master volume and which input should I choose? I have 3.
Thanks,
Jason

[nosaj]

Ok I chose the sustain channel 1 v 1khz sine input u1 pin 12 5.8v pin 10 2.4v My thinking and looking at schem is I shouldn't get a voltage at pin 10.
Shortly after this I can see what looks like not quite smoke coming from screen resistors so i power off They are yellow violet brown which says 470 ohms So tomorrow I will change them and redo tests. I will also reduce the sine input to .1 v.

Thanks, nosaj

[nickb]

Ok I chose the sustain channel 1 v 1khz sine input u1 pin 12 5.8v pin 10 2.4v My thinking and looking at schem is I shouldn't get a voltage at pin 10.
Shortly after this I can see what looks like not quite smoke coming from screen resistors so i power off They are yellow violet brown which says 470 ohms So tomorrow I will change them and redo tests. I will also reduce the sine input to .1 v.

Thanks, nosaj

Just turn everything up and use the "1&2" input. I meat to say "normal" rather that"sustain" but if it's all up then no matter.

[nickb]

Ok I chose the sustain channel 1 v 1khz sine input u1 pin 12 5.8v pin 10 2.4v My thinking and looking at schem is I shouldn't get a voltage at pin 10.
Shortly after this I can see what looks like not quite smoke coming from screen resistors so i power off They are yellow violet brown which says 470 ohms So tomorrow I will change them and redo tests. I will also reduce the sine input to .1 v.

Thanks, nosaj

If those resistors are overheating you must find the cause first. My guess is the signal amplitude is so great you passed max power and yet you have next to no sound. Turn the master down and check the resistors no longer overheat. Next test the speaker.

[nosaj]

If those resistors are overheating you must find the cause first. My guess is the signal amplitude is so great you past max power and yet you have next to no sound. Turn the master down and check the resistors no longer overheat. Next test the speaker.

I was using a 8ohm dummy load. Will follow up later today

[nosaj]

I was using a 8ohm dummy load. Will follow up later today

Replaced resistors ran .1v input all knobs into input 1and2 maxed no smoking.

U2-12 roughly 10v
U2-10 less than 1v
EQ in roughly 10v

Gonna check schematic to check out the 1458 on the eq board then report back.

Thanks, nosaj

[nosaj]

Replaced resistors ran .1v input all knobs into input 1and2 maxed no smoking.

U2-12 roughly 10v
U2-10 less than 1v
EQ in roughly 10v

Gonna check schematic to check out the 1458 on the eq board then report back.

Thanks, nosaj

And the final culprits is..........the 1458 swapped with one in junk box. BOOM full volume i think we're hear volume is on par with other 50 watters I've got.

Thanks nickb for following me through.

nosaj