Hello,
I have this Rotel RA-1570 Amplifier, and it got stuck in "AMP in Protection mode". I cant seem to be able to find its Service manual anywhere.
I have done the following:-
A.
1. Remove all inputs
2. Remove Channel A Speakers (I don't have Channel B)
3. Power on. ---> Message the same "AMP in Protection mode"
4. No smoke
5. Nothing smells of burning
6. No heated components
B.
1. Disassemble top input board to reach amp in lower level
2. Measure in Diode mode all transistors for any inconsistency. --> No probs here. All similar transistors indicate normal readouts fwd or rev. check between each channel
3. Check for open circuit BIAS resistors (0.22 ohms) --> Measure ok with 4 wire measurement with my DMM
4. Measure in Diode mode all driver Transistors. --> Indicate similar readings between each channel. No open or short circuit.
5. No blown fuses around
6. No additional extra modules present on any of the boards (usually Bluetooth or optical converters etc)
C.
1. Different voltage measurements on Bias resistors though do exists between channels
2. One channel indicates -4mv whilst the other indicates -1.89mv (quite the difference)
3. Which one is the correct ? (I would not know)
4. Asking for a Service manual --> Cant find it anywhere
5. Bias voltage is ~+58v ~-58v DC which appears on collector pins of power transistors. Emitter is 0v DC, and base is around 500mv!
Any help is disparately needed 🙂
Anyone has a manual ?
Thank you in advance !!
I have this Rotel RA-1570 Amplifier, and it got stuck in "AMP in Protection mode". I cant seem to be able to find its Service manual anywhere.
I have done the following:-
A.
1. Remove all inputs
2. Remove Channel A Speakers (I don't have Channel B)
3. Power on. ---> Message the same "AMP in Protection mode"
4. No smoke
5. Nothing smells of burning
6. No heated components
B.
1. Disassemble top input board to reach amp in lower level
2. Measure in Diode mode all transistors for any inconsistency. --> No probs here. All similar transistors indicate normal readouts fwd or rev. check between each channel
3. Check for open circuit BIAS resistors (0.22 ohms) --> Measure ok with 4 wire measurement with my DMM
4. Measure in Diode mode all driver Transistors. --> Indicate similar readings between each channel. No open or short circuit.
5. No blown fuses around
6. No additional extra modules present on any of the boards (usually Bluetooth or optical converters etc)
C.
1. Different voltage measurements on Bias resistors though do exists between channels
2. One channel indicates -4mv whilst the other indicates -1.89mv (quite the difference)
3. Which one is the correct ? (I would not know)
4. Asking for a Service manual --> Cant find it anywhere
5. Bias voltage is ~+58v ~-58v DC which appears on collector pins of power transistors. Emitter is 0v DC, and base is around 500mv!
Any help is disparately needed 🙂
Anyone has a manual ?
Thank you in advance !!
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Hello , Thanks for attending my desperate call. Yes there are are two relays (L +R).
I just assembled everything back. I spent many hours taking it apart, troubleshooting and putting it back altogether today. However I need to check this again by Monday since am travelling from tomorrow until then.
Ok what would then be the culprit in case there is DC on before the relay(s) ?Do you mean power transistor leakage ?
Many thanks
I just assembled everything back. I spent many hours taking it apart, troubleshooting and putting it back altogether today. However I need to check this again by Monday since am travelling from tomorrow until then.
Ok what would then be the culprit in case there is DC on before the relay(s) ?Do you mean power transistor leakage ?
Many thanks
A failed or misbehaving component upstream, soldering defect of the controller chip etc etc 🙂
Some photos of the internals would help understanding the situation.
Hello. As promised am back in my lab, since finished travelling. National Holiday today as it is the Cyprus Independence day.
Ok Back to our subject...
I attach a video ,cause I think it would describe better than words, the situation. In the video one can see clearly that the top PCB is actually for I/O and Logic functions, Control panel, and input selection. The lowest PCB not clearly shown is basically the amp its self. Please review the video as it describes the symptom. My actions are now to remove the amp board and examine the relay area or the relays themselves by removing them from board and check their current consumption using power supply and ammeter.
Any suggestions are welcomed ! Please forgive my shoes. were in my way 🙂
OK, some confusion on the term bias voltage but emitters at 0Vdc is good, could still be open emitter resistor?
Owners manual talks about over current and thermal protection rather than excessive Vdc... so failing in the over current sensing???
Need to find schematic of similiar amp, protection will be the same.
Hello Many thanks for replying..
Yes I can see it. I hooked my voltmeter between Gnd point and checked for DC on these coils either side just to be safe on my readings..! No DC Present
Attachments
Hello, Many thanks for your reply.
Ok I meant Power supply to the transistors is ~+58v ~-58v. Yes I have read the owners manual, and indeed it mentions that. So its over current sensing that takes AMP into protection mode. I tried to find schematics for either latest or earliest models of RA1570 with no success. However I will take your recommendation and check the emitter resistors (0.22Ω) again.
Thank you
Hello everyone. I attached an excel spreadsheet with all my measurements for each transistor and each emitter resistor
Hope that will make it easy for anyone to help me out here, cause changing transistors out of no reason is not the best
I checked the relays and they only consume 0.01A (10mA) at 24v each one. So these are not the issue I would suggest.
I ll appreciate a feedback.
Hope that will make it easy for anyone to help me out here, cause changing transistors out of no reason is not the best
I checked the relays and they only consume 0.01A (10mA) at 24v each one. So these are not the issue I would suggest.
I ll appreciate a feedback.
Above voltages look fine, they don't indicate the common "amp in protection because of high Vdc due to failed outputs/drivers/..."
Looking like there is a failure in the protection circuit, it is reporting a fault when there is none.
Without a schematic this will be difficult. The over current sensing will(?) be done at the emitter of the output transistors, ie, there will be a connection from output emitter to a resistor and/or diode then to the base of the sensing transistor. You need to find and test that transistor, looking for a b-e short.
The other possibility is thermal protection, looking for an additional device (not outputs or bias/temp compensation) mounted to heat sink.
Will try and find a rotel service manual with the above.
Looking like there is a failure in the protection circuit, it is reporting a fault when there is none.
Without a schematic this will be difficult. The over current sensing will(?) be done at the emitter of the output transistors, ie, there will be a connection from output emitter to a resistor and/or diode then to the base of the sensing transistor. You need to find and test that transistor, looking for a b-e short.
The other possibility is thermal protection, looking for an additional device (not outputs or bias/temp compensation) mounted to heat sink.
Will try and find a rotel service manual with the above.
Thanks a lot MBZ for noting all these and to look for a manual. Actually I was just getting ready to ask any of you participating in this thread to may be reach for one on your own countries because over here Distributors and Agents just ask you to bring it in. When you do they are telling you in a couple of days..."is just not worth fixing it buy a new one". I hate that answer !! incompetent people I'd say. ! Thank you once again
I attach here 3 more pictures clearly showing the allocation of parts on the Amplifier PCB. You can see my red pointer showing a part which reminds me of an HAxxxx series chip which is used for something in this whole circuit. Obviously I don't know its use. MBZ mentioned sth earlier that all pre-drivers / power amp transistor measured values seem to be ok and that may be the protection circuit is reporting false and shuts down the amp.
So am feedbacking on that line and am saying that I could not find a transistor either short circuit or open circuit with B-E shorted. Therefore all of my thoughts are focused on this IC mounted inverted on the PCB which I have not checked. May be the designers decided to avoid the use of too many transistors to "simplify" the protection circuit using that type of IC. Also that resistor am pointing is heating up. I used a friends infra red camera and looked around in that PCB. I removed the resistor and its colours match the value measured 18K
Hope that helps even more
So am feedbacking on that line and am saying that I could not find a transistor either short circuit or open circuit with B-E shorted. Therefore all of my thoughts are focused on this IC mounted inverted on the PCB which I have not checked. May be the designers decided to avoid the use of too many transistors to "simplify" the protection circuit using that type of IC. Also that resistor am pointing is heating up. I used a friends infra red camera and looked around in that PCB. I removed the resistor and its colours match the value measured 18K
Hope that helps even more
Attachments
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As I said... I removed that chip previously shown with my red pointer
Its an EMT1237B. Googled that one and it turns out that briefly is a pre-amp and speaker protection circuitry
http://www.omicomputers.com/info-stereo-amplifier-and-speaker-protection-4193.html
So...now ! Since I removed that, does that mean if I turn the amp on and play around with speaker switches (Low volume) the amp will keep on working ? without going into protection mode ?
Stay tuned !!
Its an EMT1237B. Googled that one and it turns out that briefly is a pre-amp and speaker protection circuitry
http://www.omicomputers.com/info-stereo-amplifier-and-speaker-protection-4193.html
So...now ! Since I removed that, does that mean if I turn the amp on and play around with speaker switches (Low volume) the amp will keep on working ? without going into protection mode ?
Stay tuned !!
It sure would be good to have a schematic...
Can you remove that EMT1237B "chip" and post a close-up photo of its component side?
Can you remove that EMT1237B "chip" and post a close-up photo of its component side?
Hello, I found one in local store for a 1.5 euro. I replaced it Issue still same. Followed the PDF attached and some voltages like on pin 4 is 2.4vdc pin8 is 3.4dc and pin 7 is 2.2vdc (while typically on pin 7 is 2.06V) as the pdf file says
@ostripper: Is there a known difference between EMT1237B and uPC1237 ?
Thanks
@ostripper: Is there a known difference between EMT1237B and uPC1237 ?
Thanks