Hi
Im not sure this is the right place to ask, but I am frustrated and desparated.. so hopefully some experts can give me some ideal of how to fix this amp.
I have a Rotel RMB-1095 amplifier (produced around 2003). It is a 5 channels, 200w/channel. I only connected and used 2 front channels (L,R) at lower volume (20-25% power). The amp worked well except it RANDOMLY went into protection mode!! Sometime it was 1 hour into the movies, sometime 3,4 hrs, or even every 2-3 days (RANDOMLY, unpredictable!!). When the protection mode kicked in, all 5 LED (for 5 channels) turned on, and sound disappeared (even though I only connected/used 2 front channels!!). As soon as I reset the power (On/Off), the unit worked well again until the next shut down! This unit run quite hot, but I placed 2 computer fans on top cover, so overheat should not be a problem. I tried to isolate the issue and did an experiment:
1. Connected power + signal input + speakers ...... unit shut down
2. Connected power + signal input. DISCONNECTED speakers .... unit shut down.
3. Connected only power. DISCONNECTED signal inputs ...... unit would run perfect for weeks, NO protection mode kicked in!!
Also noted, I have this same setup of speakers, cables, signal input (Denon AVR) for years with other amps... all worked perfect, so we can eliminate the speakers and cables factors.
I sent the amp to Rotel AUTHORIZED service center. Per Rotel's service bulletin, he replaced the 5 resistors (which supposed to be under voltage..etc..), rebuilt "protection power supply" board. He stated that the unit tested and worked fine. As soon as I took it home, the same protection circuit triggered again (no improvement at all!!). I had since brought it back to Rotel's technician 3 times, and he could not anything wrong with it!!
I am so frustrated and tired with this amp. I had invested more than $1500 in to this, hoping I can keep it for another 10 years.... But the protection circuit trigger drove me nut!!. I have invested too much to justify throwing it away!!. Can someone have any idea what to look for? where should I check out? which components might be the issue?? Or even any local shop that is capable of fixing these type of issues?? I am from Orange County, near Los Angeles area... dont mind driving around 100 miles radius if there is somebody around here that know how to fix it. Thank you
Im not sure this is the right place to ask, but I am frustrated and desparated.. so hopefully some experts can give me some ideal of how to fix this amp.
I have a Rotel RMB-1095 amplifier (produced around 2003). It is a 5 channels, 200w/channel. I only connected and used 2 front channels (L,R) at lower volume (20-25% power). The amp worked well except it RANDOMLY went into protection mode!! Sometime it was 1 hour into the movies, sometime 3,4 hrs, or even every 2-3 days (RANDOMLY, unpredictable!!). When the protection mode kicked in, all 5 LED (for 5 channels) turned on, and sound disappeared (even though I only connected/used 2 front channels!!). As soon as I reset the power (On/Off), the unit worked well again until the next shut down! This unit run quite hot, but I placed 2 computer fans on top cover, so overheat should not be a problem. I tried to isolate the issue and did an experiment:
1. Connected power + signal input + speakers ...... unit shut down
2. Connected power + signal input. DISCONNECTED speakers .... unit shut down.
3. Connected only power. DISCONNECTED signal inputs ...... unit would run perfect for weeks, NO protection mode kicked in!!
Also noted, I have this same setup of speakers, cables, signal input (Denon AVR) for years with other amps... all worked perfect, so we can eliminate the speakers and cables factors.
I sent the amp to Rotel AUTHORIZED service center. Per Rotel's service bulletin, he replaced the 5 resistors (which supposed to be under voltage..etc..), rebuilt "protection power supply" board. He stated that the unit tested and worked fine. As soon as I took it home, the same protection circuit triggered again (no improvement at all!!). I had since brought it back to Rotel's technician 3 times, and he could not anything wrong with it!!
I am so frustrated and tired with this amp. I had invested more than $1500 in to this, hoping I can keep it for another 10 years.... But the protection circuit trigger drove me nut!!. I have invested too much to justify throwing it away!!. Can someone have any idea what to look for? where should I check out? which components might be the issue?? Or even any local shop that is capable of fixing these type of issues?? I am from Orange County, near Los Angeles area... dont mind driving around 100 miles radius if there is somebody around here that know how to fix it. Thank you
Without making real measurements in the equipment we can only guess and this is completely useless.
Try to use a different pair of channels because all channels are identical.
Try to use a different pair of channels because all channels are identical.
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It seems that you aren't the only user with that protection shutdown problem. You might get some help and several more suggestions to try if you read this old but well-considered help thread on another forum: RMB 1095 Shuts Down
I have tried all the channels... with all the same result: random shutdown (that worked right away after reset). What upset me the most was I sent it to Rotel's authorized tech for fix... after 3 trips, the tech gave up, couldnt visually find anything wrong!!...
I totally agreed with you. Unfortunately he is the only "rotel's authorized repair shop" within 100 miles radius. I dont know much about electronics, but I believed nothing cant be fixed!!. It just a matter of taking time measure each component. Unfortunately none of the techs I talked to (around here) wanted to do that.... they wanted to replace the whole defective pcb board, which no longer available from Rotel (no longer support these models)
Thank you Ian, during my search for this issue, I did see this thread... unfortunately, it didnt offer any solution to the issue....
Keep in mind intermittent problems can be a PITA to track down
Service manual shows unit uses uPC1237(3 of) for protection functions (offset,mute,overload...).
Since all 5 LEDs indicate protection more likely to be a common function (power supply?) rather than excessive offset or... and all 3 uPC's.
Ideally would monitor Vdc to GND at the bias test points TP1,2,3,4,5 and power supply to the 3 uPC's then wait 2-3 days... Your tech will know this, diy skill would be handy but not worth the risky if you are not suited
Service manual shows unit uses uPC1237(3 of) for protection functions (offset,mute,overload...).
Since all 5 LEDs indicate protection more likely to be a common function (power supply?) rather than excessive offset or... and all 3 uPC's.
Ideally would monitor Vdc to GND at the bias test points TP1,2,3,4,5 and power supply to the 3 uPC's then wait 2-3 days... Your tech will know this, diy skill would be handy but not worth the risky if you are not suited
thank you Mbz, this information is very helpful, I will pass it on to the repair technician... hopefully he can figure it out... this issue has been dragged on for more than a year!!
Hi nguyenphananh,
You mentioned that the fault does not occur in the shop. If that is the case, I can't see your tech being able to diagnose the issue.
You could have an odd fault with your input signals. High leakage current or iffy signal commons could do it. Just because another piece of equipment seems to work doesn't clear your equipment. I would drop off the preamp / signal processor with it next time. If you have any equipment connected to cable TV, disconnect the cable connection to see if that makes a difference. Make certain you isolate all cable connections for that to work. You have to approach this from a system standpoint from what I see.
-Chris
You mentioned that the fault does not occur in the shop. If that is the case, I can't see your tech being able to diagnose the issue.
You could have an odd fault with your input signals. High leakage current or iffy signal commons could do it. Just because another piece of equipment seems to work doesn't clear your equipment. I would drop off the preamp / signal processor with it next time. If you have any equipment connected to cable TV, disconnect the cable connection to see if that makes a difference. Make certain you isolate all cable connections for that to work. You have to approach this from a system standpoint from what I see.
-Chris
Hi Chris
Thank you for the suggestion, I will definitely try what you suggested. To be clear, I have done some of the testing
1. Prior to this Rotel RMB amp, I had the exactly same setup (equipments, connection, cables..etc) connected to the Emotiva XPA-2 amp (2 channels). It worked perfect without issue. After this Rotel amp, I borrowed another Rotel RB-1070 amp (same era, same design, but 2 channels and 120w/channel) and put in place... its been working fine for months without issue.
2. Rotel's "authorized shop" claimed that he tested without issue. However, his technique of testing is very different from my using. He left it on for the whole week. At home, I only watched for 2-4 hrs at the time. As I mentioned before, after the protection kicked in, I recycled the power and the amp worked without problem for hrs, or until next day....etc.
3. Couple weeks ago, I dropped off the amp at the local TV repair shop (I think they are scammer .... but that is another story). They stated that an hour after turned on (with their preamp/player whatever), the amp went into protection mode.... but after reset, it never happened again (so they never fixed or do anything to it...except charged me!!). So with other equipment, and different environment, it happened too (eliminated my power outlet factor).
4. For the equipment and connection, I have 1 HD player (Zappiti 4k HDR) connected by HDMI, and 1 optical input from TV (my TV is older, doesnt support audio return HDMI). These connected to the Denon AVR-3311CI. Then I connected Denon's preout to Rotel's Left and Right (RCA cable). Either listening to TV (audio) or HD player will cause protection mode to kick in.
I did consider changing to another AVR to see if it will make a different, but havent find a replacement. Also the Emotiva and Rotel RB-1070 amp was working fine with this receiver, I assumed the receiver is ok....
Thank you for the suggestion, I will definitely try what you suggested. To be clear, I have done some of the testing
1. Prior to this Rotel RMB amp, I had the exactly same setup (equipments, connection, cables..etc) connected to the Emotiva XPA-2 amp (2 channels). It worked perfect without issue. After this Rotel amp, I borrowed another Rotel RB-1070 amp (same era, same design, but 2 channels and 120w/channel) and put in place... its been working fine for months without issue.
2. Rotel's "authorized shop" claimed that he tested without issue. However, his technique of testing is very different from my using. He left it on for the whole week. At home, I only watched for 2-4 hrs at the time. As I mentioned before, after the protection kicked in, I recycled the power and the amp worked without problem for hrs, or until next day....etc.
3. Couple weeks ago, I dropped off the amp at the local TV repair shop (I think they are scammer .... but that is another story). They stated that an hour after turned on (with their preamp/player whatever), the amp went into protection mode.... but after reset, it never happened again (so they never fixed or do anything to it...except charged me!!). So with other equipment, and different environment, it happened too (eliminated my power outlet factor).
4. For the equipment and connection, I have 1 HD player (Zappiti 4k HDR) connected by HDMI, and 1 optical input from TV (my TV is older, doesnt support audio return HDMI). These connected to the Denon AVR-3311CI. Then I connected Denon's preout to Rotel's Left and Right (RCA cable). Either listening to TV (audio) or HD player will cause protection mode to kick in.
I did consider changing to another AVR to see if it will make a different, but havent find a replacement. Also the Emotiva and Rotel RB-1070 amp was working fine with this receiver, I assumed the receiver is ok....
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Do you have a multimeter?
Measure with all equipment's ON, but with the source completely disconnected from the amplifier, and with multimeter set on voltage, the voltage difference between amplifier GND (from imput connector) and the GND from source (also from output connector).
Measure with all equipment's ON, but with the source completely disconnected from the amplifier, and with multimeter set on voltage, the voltage difference between amplifier GND (from imput connector) and the GND from source (also from output connector).
Hi nguyenphananh,
Sorry you ran into a hack shop. I am really tired of dealing with the aftermath from these people.
Some techs don't actually want to see the equipment fail, then have to figure it out. But, that is their job after all!
Some amplifiers have different methods for signal ground. Sometimes there is a resistor in the ground circuit that can burn open, then ground reference depends entirely on the RCA cable. Any signal on that ground can trigger protection or large DC offsets in the amplifier. There are times a ground trace can burn open as well. Because my bench is carefully laid out, this may not show up on test directly, so you have to test the grounds specifically.
It sounds like you need a better tech, and they are no longer common I'm afraid. Maybe if you look for an older audio only technician, and most work from home these days, you can find someone. One hint is that they will have all the test equipment they need in good repair, and a good parts stock. They absolutely do require a good distortion analyser, modern scope (possibly analogue, or an expensive digital) and other really good equipment. I strongly doubt you will find any half decent tech who does not maintain a good work bench. People who fix video equipment or computers are typically not a good choice.
I don't know if that helps, I hope it does.
-Chris
Sorry you ran into a hack shop. I am really tired of dealing with the aftermath from these people.
Some techs don't actually want to see the equipment fail, then have to figure it out. But, that is their job after all!
Some amplifiers have different methods for signal ground. Sometimes there is a resistor in the ground circuit that can burn open, then ground reference depends entirely on the RCA cable. Any signal on that ground can trigger protection or large DC offsets in the amplifier. There are times a ground trace can burn open as well. Because my bench is carefully laid out, this may not show up on test directly, so you have to test the grounds specifically.
It sounds like you need a better tech, and they are no longer common I'm afraid. Maybe if you look for an older audio only technician, and most work from home these days, you can find someone. One hint is that they will have all the test equipment they need in good repair, and a good parts stock. They absolutely do require a good distortion analyser, modern scope (possibly analogue, or an expensive digital) and other really good equipment. I strongly doubt you will find any half decent tech who does not maintain a good work bench. People who fix video equipment or computers are typically not a good choice.
I don't know if that helps, I hope it does.
-Chris
Thank you Sesebe and Chris. I will definitely try your suggestion. Infact, I think both of you hit the nail, or at least looking in the right direction. Like I mentioned, If I connected the signal inputs, and disconnected the speakers, the amp still shut down. But if I disconnected the signal input, then the amp will work reliably!!. so clearly the RCA signal input path has something to do with it. While I know my way around cars very well, Im a little unfamiliar with electronic. do you meant measure the - and + terminal at RCA connector? if not, I will ask the local tv repair shop to do that.
On the other hand, just like you said, I search up and down 100 miles radius around Los angeles area, none of the shop, tech now aday have the equipment, knowledge to do the proper job, or at least they are not interested to!!
On the other hand, just like you said, I search up and down 100 miles radius around Los angeles area, none of the shop, tech now aday have the equipment, knowledge to do the proper job, or at least they are not interested to!!
Hi nguyenphananh,
Do me a favour and measure the resistance between the two RCA ground shells, and from each shell to the chassis. That can tell us something.
The resistance between the signal contact and ground should be a high resistance. I didn't look at this diagram again, but I would expect somewhere between 10K and 220K resistance.
-Chris
Do me a favour and measure the resistance between the two RCA ground shells, and from each shell to the chassis. That can tell us something.
The resistance between the signal contact and ground should be a high resistance. I didn't look at this diagram again, but I would expect somewhere between 10K and 220K resistance.
-Chris
Like I said, while I know my way around machines, cars... electronic is beyond my expertise, I am almost clueless looking at the pcb board. I planned to pass on these information to the local repair technician tomorrow, hopefully he can figure out something. Anyway, armed with the multimeter, I tried to test your suggestion today. With the amp disconnected and power off, I look at behind the connectors. Unfortunately, these connector were not as basic/simple as I expected!!. I couldnt identify the GND terminal (from behind). As attached picture show. I set the multimeter at 2000 Ohms and measure between the center pin and top pin (3rd metal plate, picture), they are both + I assumed, and these are the result I got:Surround Left: 1984 Left: 1990 Center: 1995 Right: 1995 Surround Right: 1984. So look like the Left channel measurement is a little different than the Center and Right. Whatever it meant I have no ideal... just know if off from the other 2s!!. When I measured between the GND (outer shell of the connectors) and the resistors (example R409 in picture), all 5 channels showed 2.4 (with multimeter set at 200 Ohms). I know my measurement was not right and not what you were suggested... but I like said, I will ask the technician, since I dont know my way around the electronic.
BTW, I am a little confuse. I pulled off the RCA cable from my Denon (power on) and measure the voltage... didnt matter what I set (Vdc 200m, 2000m, 20, 200), it showed 0v?!. I know car stereo claimed their RCA preamp output 2.5v - 4v.... but 0v?? and it working properly?!
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Hi nguyenphananh,
Measure between the RCA shell and an exposed metal part on the case, and between the RCA shells. Then stick the probe into the RCA connector and contact the metal finger inside with the common lead on the case or RCA shell (which might be a lot easier). This is done from the outside of the case. No PCBs to worry about.
The 2.5 volt rating is probably a maximum signal level. You would measure that on the AC scale of your meter, assuming its frequency response is high enough. Normally with a 1KHz constant tone. You should definitely measure 0 VDC! 0.0mVDC if you can range that far down. The equipment is turned on for this measurement.
Be aware that with cheap meters, the frequency response may be totally inaccurate much higher than 60 Hz. Very good hand held meters may go up to 100 KHz, bench to 300 KHz. Specialized meters will measure RF frequencies, really good audio ones up to 1 MHz.
I really hope this helps you to figure this out with your technician's help. Please have him post here with any questions and we will try to help.
-Chris
Measure between the RCA shell and an exposed metal part on the case, and between the RCA shells. Then stick the probe into the RCA connector and contact the metal finger inside with the common lead on the case or RCA shell (which might be a lot easier). This is done from the outside of the case. No PCBs to worry about.
The 2.5 volt rating is probably a maximum signal level. You would measure that on the AC scale of your meter, assuming its frequency response is high enough. Normally with a 1KHz constant tone. You should definitely measure 0 VDC! 0.0mVDC if you can range that far down. The equipment is turned on for this measurement.
Be aware that with cheap meters, the frequency response may be totally inaccurate much higher than 60 Hz. Very good hand held meters may go up to 100 KHz, bench to 300 KHz. Specialized meters will measure RF frequencies, really good audio ones up to 1 MHz.
I really hope this helps you to figure this out with your technician's help. Please have him post here with any questions and we will try to help.
-Chris
Try swapping your brand of speaker cable
I once gave a friend a pair of "high definition" speaker cables for a Rotel amplifier he had just purchased. Using these made the amplifier unstable and caused the transformer to burn out. This led to a replacement being supplied.
On power up the symptoms of loud hum appeared in the replacement but my friend shut the amplifier off in a hurry - averting serious damage. The salesman was called and seeing the "high definition speaker" cables put them in the trash.
Hitherto I had not experienced instability problems with that particular brand of cable with my DIY amplifier.
I once gave a friend a pair of "high definition" speaker cables for a Rotel amplifier he had just purchased. Using these made the amplifier unstable and caused the transformer to burn out. This led to a replacement being supplied.
On power up the symptoms of loud hum appeared in the replacement but my friend shut the amplifier off in a hurry - averting serious damage. The salesman was called and seeing the "high definition speaker" cables put them in the trash.
Hitherto I had not experienced instability problems with that particular brand of cable with my DIY amplifier.
In my case, disconnected the speakers (and it cables), the amp still went into protection mode. When it worked, it worked fine, no hum.... I think we can eliminate the Speakers and it cables.
I dropped off the amp to local TV repair shop today. I showed him your messages. He seems to know and familiar with your suggestion. I will talk to him again on Wednesday for update....
I dropped off the amp to local TV repair shop today. I showed him your messages. He seems to know and familiar with your suggestion. I will talk to him again on Wednesday for update....