Go with the easiest item first - the relay. Find the coil terminals and apply 24 volts (2x 9V batteries in series will work). If it clicks the relay is ok. Measure between it's contacts when it is energised and see if it conducts
The terminals to the left of it on the picture are most likely connected to the power on delay circuit. Test that 24V is appearing here after a short delay. If not - youre looking at the control circuit being faulty.
If that all works, you need to look further. By the look of it, those 2 big white power resistors have a thermal fuse sandwiched between them. It's possible that's blown.
NOTE: I haven't read back in this thread to know how technically able you are to do any of this. Bear in mind this is working with LIVE power and can be dangerous if you're inexperienced!
The terminals to the left of it on the picture are most likely connected to the power on delay circuit. Test that 24V is appearing here after a short delay. If not - youre looking at the control circuit being faulty.
If that all works, you need to look further. By the look of it, those 2 big white power resistors have a thermal fuse sandwiched between them. It's possible that's blown.
NOTE: I haven't read back in this thread to know how technically able you are to do any of this. Bear in mind this is working with LIVE power and can be dangerous if you're inexperienced!
OK, i've now reviewed the thread. Sorry, but if you aren't comfortable with testing and measuring a live circuit, you will have to stop here and get the amp professionally repaired. Better to spend some money than to risk your own life.
I would say I'm somewhat experienced, and I've had a few, nasty close calls that make me quadruple check everything when i'm doing any work with mains power.
I would say I'm somewhat experienced, and I've had a few, nasty close calls that make me quadruple check everything when i'm doing any work with mains power.
Thanks for that Jaycee, i understand and would take it to someone with more experience than i but the fact is that i am unemployed due to the credit crunch and simply have no money. What i do have is time and since working on this amp i have tought myself (with the help of some great folk on this site) some very invaluable lessons in electronics. I am very passionate about learning electronics, to the point that i am considering going back to college to do a course in electronics.
I have worked with live circuits and through not being completely confident i know not to rush but to take real caution and make sure that i have prepared before powering on.
Truth is, with your experience, i would have said the same thing to me.
I will check the relay first and take it from there.
I have worked with live circuits and through not being completely confident i know not to rush but to take real caution and make sure that i have prepared before powering on.
Truth is, with your experience, i would have said the same thing to me.
I will check the relay first and take it from there.
I have just desoldered R901 and R902 (big resistors next to relay in picture 1) and also TH901 (thermostat) which are all taped together. The thermostat/thermal fuse tests good for continuity but the resistors have no continuity nor do they show any resistance.
The part No for the resistors are RWH20G10RJ and they have 'MEGGITT SBCHE 11 CGS 10R J DL JM printed on each one. In the srvice manual, it states that it is resistor 20W 10.
The part No for the resistors are RWH20G10RJ and they have 'MEGGITT SBCHE 11 CGS 10R J DL JM printed on each one. In the srvice manual, it states that it is resistor 20W 10.
I'd say you found the problem 🙂
Getting exact replacements could be tricky. What i'd probably do here is to use an aluminium clad resistor and mount it in the case somewhere. Assuming the two resistors were in parallel, that'd mean about 5 ohms at 40W. A 6R8 ohm resistor would work, and you can get 50W aluminium clad ones.
This also shows that the thermal fuse did not work as intended - if it had done so, it would have opened before the resistors did.
I wonder what the thermistor is there for...
edit: This part looks suitable as a direct replacement:
http://cpc.farnell.com/unbranded/lsr-100-10/resistor-audio-10w-10r/dp/RE04031?_requestid=458749
edit 2: Meh, CPC are ambiguous. At the top it says 10W. In the description it says 20W. The parametric search says it's 20W too. Looking at it, it's really 10W
I wouldn't mess about, and I'd replace them both with one of these:
http://cpc.farnell.com/welwyn/wh50-5r-ji/resistor-ww-50w-5-5r/dp/RE03490?_requestid=459186
Getting exact replacements could be tricky. What i'd probably do here is to use an aluminium clad resistor and mount it in the case somewhere. Assuming the two resistors were in parallel, that'd mean about 5 ohms at 40W. A 6R8 ohm resistor would work, and you can get 50W aluminium clad ones.
This also shows that the thermal fuse did not work as intended - if it had done so, it would have opened before the resistors did.
I wonder what the thermistor is there for...
edit: This part looks suitable as a direct replacement:
http://cpc.farnell.com/unbranded/lsr-100-10/resistor-audio-10w-10r/dp/RE04031?_requestid=458749
edit 2: Meh, CPC are ambiguous. At the top it says 10W. In the description it says 20W. The parametric search says it's 20W too. Looking at it, it's really 10W
I wouldn't mess about, and I'd replace them both with one of these:
http://cpc.farnell.com/welwyn/wh50-5r-ji/resistor-ww-50w-5-5r/dp/RE03490?_requestid=459186
Thanks Jaycee,
yes it is tricky to get hold of. I have just done a search on google to no avail.
There is a 20w 10 ohm resistor on ebay but it looks totally different and the pins are not wide enough apart.
yes it is tricky to get hold of. I have just done a search on google to no avail.
There is a 20w 10 ohm resistor on ebay but it looks totally different and the pins are not wide enough apart.
What makes this confusing is that on the service manual there is no R902. It just states R901 being a 20w 10r resistor but in actual fact there are 2 10r resistors but i don't know there wattage. Would it be 11w as on the resistor it states 'meggitt sbche 11 cgs 10r j dl jm'. The print on the resistor is the only thing i can go by.
Maplins do some 10w wirewound 10r resistors that will fit perfectly, so could i use 2 of these? If so i can go a collect today and get them soldered in straight away.
Maplins do some 10w wirewound 10r resistors that will fit perfectly, so could i use 2 of these? If so i can go a collect today and get them soldered in straight away.
Ah - yes then, it is likely that they are using 2x 10W resistors. The maplin devices should be suitable.
One thing I would advise you do, is to get yourself an IEC kettle lead, and splice a lamp socket in series with the Live wire. Before powering up after youve replaced the resistors, use this modified cable with a 60W light bulb in the socket. This serves as a safety device - if you have a fault, the bulb will light up and save the circuit from damage.
One thing I would advise you do, is to get yourself an IEC kettle lead, and splice a lamp socket in series with the Live wire. Before powering up after youve replaced the resistors, use this modified cable with a 60W light bulb in the socket. This serves as a safety device - if you have a fault, the bulb will light up and save the circuit from damage.
Ok will do.
Would you put the amp pcb's back in before power on? Or just leave it in present state (last picture)?
Would you put the amp pcb's back in before power on? Or just leave it in present state (last picture)?
I'd leave the actual power amps themselves disconnected, and test the power supply part. Make sure nothing can short - use insulation tape over the loose wires that would connect the power amps.
Once you have confirmed the power supply powers up and produces the correct voltages, you can move on to reconnecting the power amp modules.
I'd recommend you buy a 1Kohm 10W resistor and use this to discharge the supply - those capacitors can store a hell of a lot of charge even after power off. You can connect the 1K resistor over each capacitor (using suitable crocodile clip leads) to "bleed" them after power off before doing anything else.
Once you have confirmed the power supply powers up and produces the correct voltages, you can move on to reconnecting the power amp modules.
I'd recommend you buy a 1Kohm 10W resistor and use this to discharge the supply - those capacitors can store a hell of a lot of charge even after power off. You can connect the 1K resistor over each capacitor (using suitable crocodile clip leads) to "bleed" them after power off before doing anything else.
Ok, well i installed the new resistors (2 x 10w 10r wirewound high power) powered the unit up with a 60w light bulb in series with the live and the power light on the rotel came on for a split second then off. The new resistors are blown again.
The light bulb did not light at all.
There must be something else gone around that area that is making those resistors blow, but what?
I suppose i am just one step nearer to fixing my amp.
The light bulb did not light at all.
There must be something else gone around that area that is making those resistors blow, but what?
I suppose i am just one step nearer to fixing my amp.
Have you checked the lyts in power supply for shorts ?
Remember this is dangeros work. Drain them over night with a resistor, to be shure there´s no power left, before you desolder and messure them one by one.
Remember this is dangeros work. Drain them over night with a resistor, to be shure there´s no power left, before you desolder and messure them one by one.
Yes have just checked for continuity of power supply and it is all good.
Decided to de-solder everything on the same pcb as the resistors and have found a fault with the relay. I opened the relay up and there is burn marks on both terminals and when i manually close the realy, there is no continuity from the pins underneath. I will order a new one. Although the service manual suggests a 12v relay, in actual fact it is a 24v relay.
I also desoldered the thermistor which tests well for continuity but are there other tests i should be doing on this?
Also the spark killer (c920) was desoldered, it measures no continuity which is ok right? but the pins are not long enough to reach the contacts in my DMM to test properly. How can i test this?
The diode tests good also.
Decided to de-solder everything on the same pcb as the resistors and have found a fault with the relay. I opened the relay up and there is burn marks on both terminals and when i manually close the realy, there is no continuity from the pins underneath. I will order a new one. Although the service manual suggests a 12v relay, in actual fact it is a 24v relay.
I also desoldered the thermistor which tests well for continuity but are there other tests i should be doing on this?
Also the spark killer (c920) was desoldered, it measures no continuity which is ok right? but the pins are not long enough to reach the contacts in my DMM to test properly. How can i test this?
The diode tests good also.
What's your e-mail - I think I have RB-1090 schematic that coresponds to your amplifier version? I'll send it to you and it'll be easier for you to sort it out.
If the relay didn't close, the resistors will burn out. They're not meant to take the load for anything more than a second or two. This is why I prefer the aluminium clad types - they take a lot more punishment.
I'd be tempted to test the transformer without the softstarter. The light bulb in series with the live would softstart it enough for a test.
I'd be tempted to test the transformer without the softstarter. The light bulb in series with the live would softstart it enough for a test.
dayking79, did you ever get to the bottom of your troubled 1090? I have a problem that is turning out to be remarkably similar to yours...
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