Fender Roc Pro 1000 - Problem with channel distortion

[adiorgelis]

Hello!!!
recently bought an amplifier Roc Pro 1000 and it came with a defect.
How many know it has 3 channels, Clean 1 and 2 Distortion, my amp is only running the Distortion channel 2.
I really need your help to help me solve this problem.

the defect is in the following proportion:
Clean channel is perfect;
Channel 2 Distortion is perfect
Distortion channel 1 when I change the switch or the manual selector switch nothing happens, the LED does not light simply does nothing.

[52 Bill]

Clean channel is perfect;
Channel 2 Distortion is perfect
Distortion channel 1 when I change the switch or the manual selector switch nothing happens, the LED does not light simply does nothing.

Welcome! So the yellow channel works, but the red doesn't?

This amp uses a fairly complex channel switching circuit that uses fet transistors and control voltages to change the channels. If you go to the Fender site, you can download the schematic there and then use it to trace out where the problem is.

What sort of test equipment do you have and what sort of skills do you have regarding electronics?

[adiorgelis]

Welcome! So the yellow channel works, but the red doesn't?

This amp uses a fairly complex channel switching circuit that uses fet transistors and control voltages to change the channels. If you go to the Fender site, you can download the schematic there and then use it to trace out where the problem is.

What sort of test equipment do you have and what sort of skills do you have regarding electronics?

I already have the schematic in hand, I use a multimeter to make measurements, to answer your question, the yellow channel operate normally while red no sign of any.

[Enzo]

Look at the switching circuit for the test point voltages, and see if ALL of yours are changing as they should, and if not, which ones are not.

[52 Bill]

Check Test Point TP31 which is connected to pins 2 and 6 of IC U8. Depending upon what channel is selected, there are three different voltage levels that should appear here, 0-7-14 volts.

If the amp is not switching into red distortion mode, then you should only get two of the voltage levels here. If this is true and you can't get the 7 volt level there, then test diodes CR43 and CR44, as well as the gain select switch S2.

Doing these tests will require you to read voltage with the amp turned on and connected to the ac power line. If you don't know how to do this safely, then find someone that does to help you, or send the amp in to a qualified tech.

[adiorgelis]

Check Test Point TP31 which is connected to pins 2 and 6 of IC U8. Depending upon what channel is selected, there are three different voltage levels that should appear here, 0-7-14 volts.

If the amp is not switching into red distortion mode, then you should only get two of the voltage levels here. If this is true and you can't get the 7 volt level there, then test diodes CR43 and CR44, as well as the gain select switch S2.

Doing these tests will require you to read voltage with the amp turned on and connected to the ac power line. If you don't know how to do this safely, then find someone that does to help you, or send the amp in to a qualified tech.

Clean
IC 8 = 4,50 V
CR43 = 0 V
CR44 = 0 V

Drive Yellow
IC 8 = 6,60 V
CR43 = 0 V
CR44 = 0 V

Drive Red
IC 8 = 2,17 V
CR43 = 1,30 V
CR44 = 1,82 V

CR47
Clean 0,5 V
Yellow - 6,82 V
Red - 3,42 V

CR46
Clean 0,6 V
Yellow - 3,40 V
Red - 0,62 V

CR50
Clean 0,6 V
Yellow - 10 V
Red - 0,6 V

CR51
Clean 10 V
Yellow - 0,62 V
Red - 10 V

with these voltages there, what did you think? the IC is defective? or are the CR's?

[52 Bill]

CR47
Clean 0,5 V
Yellow - 6,82 V
Red - 3,42 V

with these voltages there, what did you think? the IC is defective? or are the CR's?

I don't understand any of these numbers that you have posted, but what seems to be true is that all of the control voltages are off.

Please do the following tests. On the board locate resistor R127, 1K 1Watt (it should be the large resistor next to the footswitch jack). First with the power off read the resistance across the resistor, it should be about 1K. Make sure the footswitch in not plugged into the amp for now.

Next set you meter to read AC voltage. Connect the black lead to the metal chassis and turn on the power to the amp. With the red meter lead, read the AC voltage on both ends of R127. There should be around 30VAC.

Next set you meter to read DC voltage. Connect the black lead to the metal chassis and turn on the power to the amp. With the red meter lead, read the DC voltage on the stripe end of CR47. The voltage there should change depending on what channel is selected. When the clean channel is selected, there should be about +0.5VDC. When the yellow channel is on, there should be about +14VDC and when the red channel is selected, there should be about +7VDC.

If these voltage readings are not right, you will need to find out why.

[g1]

Here's the schematic
Roc_Pro_1000_schematic.pdf

[adiorgelis]

I don't understand any of these numbers that you have posted, but what seems to be true is that all of the control voltages are off.

Please do the following tests. On the board locate resistor R127, 1K 1Watt (it should be the large resistor next to the footswitch jack). First with the power off read the resistance across the resistor, it should be about 1K. Make sure the footswitch in not plugged into the amp for now.

Next set you meter to read AC voltage. Connect the black lead to the metal chassis and turn on the power to the amp. With the red meter lead, read the AC voltage on both ends of R127. There should be around 30VAC.

Next set you meter to read DC voltage. Connect the black lead to the metal chassis and turn on the power to the amp. With the red meter lead, read the DC voltage on the stripe end of CR47. The voltage there should change depending on what channel is selected. When the clean channel is selected, there should be about +0.5VDC. When the yellow channel is on, there should be about +14VDC and when the red channel is selected, there should be about +7VDC.

If these voltage readings are not right, you will need to find out why.

tested and all voltages and values are correct as described above.

[52 Bill]

tested and all voltages and values are correct as described above.

Then if the channels still do not work, U8 is suspect.

Find CR59 and measure the voltage at the stripe end when yellow is selected and when red is selected. There should be +15vdc when red is selected, and -15vdc when yellow is selected.

[adiorgelis]

Then if the channels still do not work, U8 is suspect.

Find CR59 and measure the voltage at the stripe end when yellow is selected and when red is selected. There should be +15vdc when red is selected, and -15vdc when yellow is selected.

measure the voltage of CR59 and they are as described above

[g1]

tested and all voltages and values are correct as described above.

This is a bit confusing. I think what you mean is the voltages are what you listed in post #6, which are actually incorrect compared to the schematic.
So right at TP31 (pin 2&6 of U8, CR47 cathode), you get Clean 0,5 V, Yellow - 6,82 V, Red - 3,42 V. Do you mean those are negative voltages? According to the schematic yellow should be 14V and red should be 6.9V. As the voltages going in to U8 are already incorrect, the problem should be before U8.
Have you checked all diodes CR39 through to CR49?
Do you get the same results with the no footswitch connected as when footswitch is in use?
You said one of the LED's does not light, did you check it?

[g1]

Also, for the voltages listed in post #6, you did not specify where exactly you are measuring. U8, but which pin #? Which side of the diodes you listed, cathode or anode? Please relist your voltages with the exact locations listed.

[adiorgelis]

Also, for the voltages listed in post #6, you did not specify where exactly you are measuring. U8, but which pin #? Which side of the diodes you listed, cathode or anode? Please relist your voltages with the exact locations listed.

IC8 was measured with the tips of the multimeter pins 2 and 6
the new measurement of CRs tip black chassis and red diodes on the listed
Clean
IC 8 = 4,50 V
CR43 = 0 V
CR44 = 0 V

Drive Yellow
IC 8 = 6,60 V
CR43 = 0 V
CR44 = 0 V

Drive Red
IC 8 = 2,17 V
CR43 = 1,30 V
CR44 = 1,82 V

CR47
Clean 0,5 V
Yellow - 6,82 V
Red - 3,42 V

CR46
Clean 0,6 V
Yellow - 13,25 V
Red - 6,39 V

CR50 - negative
Clean - 6.42 V
Yellow - 6,52 V
Red - 6,42 V

CR51 negative
Clean -6,42 V
Yellow - 6,52 V
Red - 6,42 V

[adiorgelis]

This is a bit confusing. I think what you mean is the voltages are what you listed in post #6, which are actually incorrect compared to the schematic.
So right at TP31 (pin 2&6 of U8, CR47 cathode), you get Clean 0,5 V, Yellow - 6,82 V, Red - 3,42 V. Do you mean those are negative voltages? According to the schematic yellow should be 14V and red should be 6.9V. As the voltages going in to U8 are already incorrect, the problem should be before U8.
Have you checked all diodes CR39 through to CR49?
Do you get the same results with the no footswitch connected as when footswitch is in use?
You said one of the LED's does not light, did you check it?

tests with footswitch disconnected, using only the keys of the amplifier