Rotel RB 1090 for repair in the shop works and measures properly at all functions ....Though protection is trigger happy when load is 4 R.
Surprisingly got another one for repair which had soft start issues that are already fixed and doesn't present this style of sensitivity ....
One reason could be the capacitors in the protection area one of them at fault might made the protection circuit trigger happy ....Kinda rear for Rotel, Kinda rear to happen for both ch. checked and and replaced no effect .
Protection IC has common for both ch dedicated PSU any fault there could make the protection trigger happy cheked and replaced no effect
Soft start relay could be at fault ( quite common ) and demands go up contacts ark and this triggers protection checked no findings there ....
No sign of offset there at all times
Next will be to split the protection circuit to understand if this is coming from overvoltage protection at the output or over current protection .
Next will be a comparison between the two amplifiers to see if any of the parts is different... ( fault amplifier appears to be alike the schematic Working amplifier might have a revision in the protection circuit that makes it less trigger happy ) Will have to check that ....
Any one been there before please let me know ...
Kind regards
Sakis
Surprisingly got another one for repair which had soft start issues that are already fixed and doesn't present this style of sensitivity ....
One reason could be the capacitors in the protection area one of them at fault might made the protection circuit trigger happy ....Kinda rear for Rotel, Kinda rear to happen for both ch. checked and and replaced no effect .
Protection IC has common for both ch dedicated PSU any fault there could make the protection trigger happy cheked and replaced no effect
Soft start relay could be at fault ( quite common ) and demands go up contacts ark and this triggers protection checked no findings there ....
No sign of offset there at all times
Next will be to split the protection circuit to understand if this is coming from overvoltage protection at the output or over current protection .
Next will be a comparison between the two amplifiers to see if any of the parts is different... ( fault amplifier appears to be alike the schematic Working amplifier might have a revision in the protection circuit that makes it less trigger happy ) Will have to check that ....
Any one been there before please let me know ...
Kind regards
Sakis
Hi,
it can be a fault of output device(s). The protection monitoring the emitter current of only one NPN output transistor. If any of the other 3 is not working, the increased emitter current of the monitored one will activate the protection.
Sajti
it can be a fault of output device(s). The protection monitoring the emitter current of only one NPN output transistor. If any of the other 3 is not working, the increased emitter current of the monitored one will activate the protection.
Sajti
Will check but i dont think so machine that has any output issues doesn't deliver 700W rated power before clipping
But yes i will check that also
To take your opinion as valid there is only two conditions one that any of outputs is "open" extremelly rear for MOT 200 Sanken And/or a emitter resistor is open "more possible".
will see
Then again the same type of fault for both ch ???? That will be odd
Hi Sakis
Perhaps we are looking at different schematics but there are 2 of everything in RB1090, 1090-2 and 1090-3 at least. There appear to be 2 complete amplifiers including their own uPC1237 protection circuits, each on its own mirror-image PCB.
ROTEL RB 1090 Service Manual download, schematics, eeprom, repair info for electronics experts
Perhaps we are looking at different schematics but there are 2 of everything in RB1090, 1090-2 and 1090-3 at least. There appear to be 2 complete amplifiers including their own uPC1237 protection circuits, each on its own mirror-image PCB.
ROTEL RB 1090 Service Manual download, schematics, eeprom, repair info for electronics experts
That is correct Ian these are totally individual amplifiers fault though is common for both amps ( both Boards )
I would check the ressitors on the base, and emitter of the NPN output devices.
I guess, that it deliver the rated power if one transistor is not working. Resistive load is not as critical.
Same type of fault is not common same time, but it can be a faulty series of resistors.
Sajti
Mike is working with the amp and a minute ago he said to me that at some point while measuring various conditions on the amp around clipping behavior his test point for the scope was on the board meaning before protection relay .
He noticed that at protection mode and that means amplifier is working but output relay is not engaged that output ( audio signal ) increased by some 15 volts up when the load is disconencted ...
That clearly points to main capacitors .....
We are checking that as we speak
He noticed that at protection mode and that means amplifier is working but output relay is not engaged that output ( audio signal ) increased by some 15 volts up when the load is disconencted ...
That clearly points to main capacitors .....
We are checking that as we speak
Checked with the working amplifier main capacitors appear to produce the same current and the same ripple
AC loss detect is formed with one diode one resistor and one 4.7uf cap Often you find issues there...Its powered from the one of the main transformers .
For ch A trafo features only rail voltage and for ch B it features rail voltage and AUX power supply feeding the protection and the balanced input card ...
Condition will be either a resistor partially open a diode with a leak and when the machine is fully loaded the voltage drop on the AC side is too much or marginal and protection thinks that AC is gone or too low and then protection is active
For ch A trafo features only rail voltage and for ch B it features rail voltage and AUX power supply feeding the protection and the balanced input card ...
Condition will be either a resistor partially open a diode with a leak and when the machine is fully loaded the voltage drop on the AC side is too much or marginal and protection thinks that AC is gone or too low and then protection is active
No emitter resistor appears to have any issue and no base stopper also Later i will verify that once more while the amplifier is at full load
In comparison with the "working amplifier " we noticed that fault amplifier is missing a couple of electrolytics on the circuit
Both of them a related to protection circuit
Its C701 and 702 pin 1 of protection IC and C717 next to Q 749 that sums either overload detection or high temp to feed the protection IC
Seems that the "fault" amplifier never been messed around in the past and also seems by numbers that the fault amplifier has a far smaller serial number than the working one
We install them and post here
Both of them a related to protection circuit
Its C701 and 702 pin 1 of protection IC and C717 next to Q 749 that sums either overload detection or high temp to feed the protection IC
Seems that the "fault" amplifier never been messed around in the past and also seems by numbers that the fault amplifier has a far smaller serial number than the working one
We install them and post here
schematic is drawn wrong protection IC circuit is supposed to be identical buth they are not I think i have to pull out the working amplifier to find out which is the correct circuit
Pins 1 and 2 are configured wrong in the schematic capacitor exists in pin 1 in the one side and capacitor doesn't exist on pin 1 of the other ch
Mess
Pins 1 and 2 are configured wrong in the schematic capacitor exists in pin 1 in the one side and capacitor doesn't exist on pin 1 of the other ch
Mess
OK protection scheme appears different in the available schematics of the company
As you see it the upper schematic is wrong around IC 701
The schematic of the lower IC 702 appears to be the correct one
On the existing schematic and on my faulty amplifier Pin 3 goes to ground through capacitor 709 22nf
On my working amplifier RB 1090 later serial number pin 3 goes to ground directly
So you have a pretty messed up schematic existing on the net and a pretty messed up PCB on the earlier models of 1090....
As you see it the upper schematic is wrong around IC 701
The schematic of the lower IC 702 appears to be the correct one
On the existing schematic and on my faulty amplifier Pin 3 goes to ground through capacitor 709 22nf
On my working amplifier RB 1090 later serial number pin 3 goes to ground directly
So you have a pretty messed up schematic existing on the net and a pretty messed up PCB on the earlier models of 1090....
Closing argument
For earlier RB 1090 that appear to have trigger happy protection circuits usually in difficult loads of 4R ....
Please correct all factory mods done on the pcb following the part of the schematic that is around Protection IC 702
The IC 701 is supposed to be alike but it seems that is drawn wrong .
C 701 and 702 has to be installed according to the placement and schematic of IC 702
Add capacitors C717 and C718 if missing from your amplifier
IN later models also appears that C709 22nf is no longer there and Pin 3 of the IC goes directly to ground . But this has only to do with the reset of protection In earlier models when the unit is on protect for any reason protection will not reset if the condition of the fault no longer exists unless you restart the amplifier . In later models and without the capacitor C 709 protection will reset if the fault condition no longer exists ( like High temperature )
Amp is up and running
For earlier RB 1090 that appear to have trigger happy protection circuits usually in difficult loads of 4R ....
Please correct all factory mods done on the pcb following the part of the schematic that is around Protection IC 702
The IC 701 is supposed to be alike but it seems that is drawn wrong .
C 701 and 702 has to be installed according to the placement and schematic of IC 702
Add capacitors C717 and C718 if missing from your amplifier
IN later models also appears that C709 22nf is no longer there and Pin 3 of the IC goes directly to ground . But this has only to do with the reset of protection In earlier models when the unit is on protect for any reason protection will not reset if the condition of the fault no longer exists unless you restart the amplifier . In later models and without the capacitor C 709 protection will reset if the fault condition no longer exists ( like High temperature )
Amp is up and running
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