Lee, I have just bought an RA3001. It was sold as not working and as I suspected the 47R soft-start resistor has gone o/c along with the 2A fuse. I had one of these amps from new 1o years ago and it did the same thing then. I phoned C-Audio at the time and they sent me a new resistor and told me there was a mod I could do which involved pulling a diode or resistor on the board - I can't remeber which. Can you help.
Thanks
Adrian.
Thanks
Adrian.
Hi Adrian,
1. you have an RA3001, therefore this already has the mod tracked in
2. the soft start fuse IS NOT 2Amp, it MUST be F1.6A
3. the soft start resistor must be 47R
that said, it is almost certain that you have a further fault on the unit.
My suggestion is to start by ensuring that the above are rectified and then prepare a mains lead with a light bulb in series with the live wire and armed with this give me a call on 07799386256 or 07768551482 and i should be able to talk you through a diagnosis.
Lee
1. you have an RA3001, therefore this already has the mod tracked in
2. the soft start fuse IS NOT 2Amp, it MUST be F1.6A
3. the soft start resistor must be 47R
that said, it is almost certain that you have a further fault on the unit.
My suggestion is to start by ensuring that the above are rectified and then prepare a mains lead with a light bulb in series with the live wire and armed with this give me a call on 07799386256 or 07768551482 and i should be able to talk you through a diagnosis.
Lee
Hi Lee,
I've got an RA3000 with an interesting fault. I've had this one since new, but its been in storage for about 5 years.
When i took it out recently and checked it over it seems to have turned into a low-pass filter.
putting a 1kHz sine into it (with no load) gives me a sine out at low levels... as i increase the level the sine turns into a pretty perfect triangle wave.
At 1 kHz it is not possible to get full amplitude out of the amp.
Both channels behave identically. The 15V, 90V and 100V rails all seem fine, I've also injected the signal after the Input op-amps, with the same result.
Running a frequency sweep shows that the amp is working well at, say, 100Hz, but it's behaving as a LP filter as i increase the freq.
Any ideas?
jonathan
I've got an RA3000 with an interesting fault. I've had this one since new, but its been in storage for about 5 years.
When i took it out recently and checked it over it seems to have turned into a low-pass filter.
putting a 1kHz sine into it (with no load) gives me a sine out at low levels... as i increase the level the sine turns into a pretty perfect triangle wave.
At 1 kHz it is not possible to get full amplitude out of the amp.
Both channels behave identically. The 15V, 90V and 100V rails all seem fine, I've also injected the signal after the Input op-amps, with the same result.
Running a frequency sweep shows that the amp is working well at, say, 100Hz, but it's behaving as a LP filter as i increase the freq.
Any ideas?
jonathan
Sounds like the line fuses are missing or o/c the fuses are alongside the heatsink either side of the TX.
with these out (off load) you will get a sine wave at low levels but when you turn the level up it will look triangular. if you turn the amp off at this point and drop the line fuses down you should see a decaying sinewave with both fuses in, if when you drop a fuse the output disapears then you have a fault on the output stage.
one thing this amp suffers from is loose fuses in the fuse holders. sometimes on load you can hear them signing along to the audio. remove the fuse, and with an insulated pair of pliers squeeze the fuse lugs together, when refitting the fuse drop it down so it is central on the fuse lugs and then press down in the middle to ensure both ends pop in at the same time, if the fuse topples and only goes in one side then start again as you will have bent the lugs and be back where you started.
Alternately remove the fuses and holders and fit 10A fuse wire across the points and solder into position, I find these rarely come loose.
Let me know what you find.
Lee
with these out (off load) you will get a sine wave at low levels but when you turn the level up it will look triangular. if you turn the amp off at this point and drop the line fuses down you should see a decaying sinewave with both fuses in, if when you drop a fuse the output disapears then you have a fault on the output stage.
one thing this amp suffers from is loose fuses in the fuse holders. sometimes on load you can hear them signing along to the audio. remove the fuse, and with an insulated pair of pliers squeeze the fuse lugs together, when refitting the fuse drop it down so it is central on the fuse lugs and then press down in the middle to ensure both ends pop in at the same time, if the fuse topples and only goes in one side then start again as you will have bent the lugs and be back where you started.
Alternately remove the fuses and holders and fit 10A fuse wire across the points and solder into position, I find these rarely come loose.
Let me know what you find.
Lee
hmm - i guess its possible that the fuses are o/c.
i'm nowhere near the amp or cct layout at the moment as i'm not due in my workshop for another 3 weeks.
are you suggesting that the LT (75V) rails can charge up from the HT rails ?
i was getting 98V HT and about 90V LT (which i thought was a little high).
would this explain the low-pass behavior of the amp with no load ?
i was getting 6dB/oct rolling off at about 200Hz.
i'll post what i find next time i'm in the workshop, although its at he back of the q now - i've got 14 crowns to do first for a paying client
thanks again,
jonathan
i'm nowhere near the amp or cct layout at the moment as i'm not due in my workshop for another 3 weeks.
are you suggesting that the LT (75V) rails can charge up from the HT rails ?
i was getting 98V HT and about 90V LT (which i thought was a little high).
would this explain the low-pass behavior of the amp with no load ?
i was getting 6dB/oct rolling off at about 200Hz.
i'll post what i find next time i'm in the workshop, although its at he back of the q now - i've got 14 crowns to do first for a paying client
thanks again,
jonathan
Hi Lee, thanks for your help on the phone. I have found the defective 'fet, a P channel BUZ905s, and have removed it. The bulb now dims and everything seems to work OK. I have ordered the part - a 905 - no 's' designation for Monday. Can you remind me what I need to do now with regard to checking the other 'fet's for possible wear and tear.
Thanks
Adi.
Thanks
Adi.
switch the amp on and with no signal and no load (Quiescent state) using a DMM set to mV range measure across each gate resistor (Not with respect to ground but across the resistor legs) you should have ZERO volts drop, any voltage here even 5mV will indicate a soft FET and will need to be replaced. failure to replace them will lead to their demise and the probable weakening of other and it then become a viscous circle.
on the plus side you may have none or just one other which is dodgy. it is incredibly rare to have a whole lot of FETs fail so rare i would not suspect it unless there were some obvious outside cause.
the S suffix indicate a single die device the D suffix indicates a double die device. you only require the single die device in an RA.
thanks
Lee
on the plus side you may have none or just one other which is dodgy. it is incredibly rare to have a whole lot of FETs fail so rare i would not suspect it unless there were some obvious outside cause.
the S suffix indicate a single die device the D suffix indicates a double die device. you only require the single die device in an RA.
thanks
Lee
RA4001
Hi
A friend of mine have tried to repair this beast.
5 MOSFET's were gone to the eternal transistor heaven, all in the same channel. ( 4x 2SJ162 + one 2SK1058)
He purchased new ones, and replaced the faulty ones.
And he replaced the fuse in series with the softstart resistor with a new one, only problem was that this was a T10A fuse...
He switched on the amp, and at least 4 of the new MOSFET's went the same way as the old ones.
He then sendt the amp to me....
I followed Lee's advice (60W light bulb trick), and found that the softstart resistor was defect.
In lack of a replacement resistor, I replaced it with this light bulb, and disconnected power wires from PSU to the MOSFET's, and switched on the amp.
The light bulb glows brightly and dim down slowly, so PSU and brigdes seems OK.
Meassures +/- 68V and + 6V from PSU - I think this is normal, but can anyone confirm this?
I would love to have diagrams for this amp...
The new MOSFET's did not have a branding, so I can't tell if this is a Hitachi/Renesas one, but I guess they were not good enough for this amp.
Any sugestions on what went wrong?
And what to look for, before I replace the MOSFET's?
Best regards,
Alf Gunnar Sørensen
Hi
A friend of mine have tried to repair this beast.
5 MOSFET's were gone to the eternal transistor heaven, all in the same channel. ( 4x 2SJ162 + one 2SK1058)
He purchased new ones, and replaced the faulty ones.
And he replaced the fuse in series with the softstart resistor with a new one, only problem was that this was a T10A fuse...
He switched on the amp, and at least 4 of the new MOSFET's went the same way as the old ones.
He then sendt the amp to me....
I followed Lee's advice (60W light bulb trick), and found that the softstart resistor was defect.
In lack of a replacement resistor, I replaced it with this light bulb, and disconnected power wires from PSU to the MOSFET's, and switched on the amp.
The light bulb glows brightly and dim down slowly, so PSU and brigdes seems OK.
Meassures +/- 68V and + 6V from PSU - I think this is normal, but can anyone confirm this?
I would love to have diagrams for this amp...
The new MOSFET's did not have a branding, so I can't tell if this is a Hitachi/Renesas one, but I guess they were not good enough for this amp.
Any sugestions on what went wrong?
And what to look for, before I replace the MOSFET's?
Best regards,
Alf Gunnar Sørensen
I'm not familiar with the RA4000, i had a feeling the 2SJ162 + 2SK1058's were obsolete ?
I have to say that simply replacing dead output devices and switching it back on is NOT the way to repair an amp (ok.. it works with old peaveys).
you really need to go through a complete procedure of testing with a low voltage current limited power supply to establish that the amp is behaving correctly before you hook it up to the mains.
lee here is very good with the C-audio's so hopefully he'll help you if he's not too busy.
jonathan
I have to say that simply replacing dead output devices and switching it back on is NOT the way to repair an amp (ok.. it works with old peaveys).
you really need to go through a complete procedure of testing with a low voltage current limited power supply to establish that the amp is behaving correctly before you hook it up to the mains.
lee here is very good with the C-audio's so hopefully he'll help you if he's not too busy.
jonathan
SRX3801
Hi Lee, cant e-mail you yet until i'm an 'upgraded' member !
Just like to thank you for your advice with my SRX3801. Two soft output devices replaced and the amp has stopped overheating.
With only about 5mV across the gate resistors this was not enough to bring the protect in, hence throwinig me a little.
In the past with the many XR and RA amps we have used for PA work the 2SJ and 2SK devices seem to fail and bring in the protect circuit immediately and then the light bulb trick sorts the down time out pretty quickly.
Hope the new modular amps and powered speakers are going well for you and keep up the posts on here as your advice is of great help to a many of us.
Hi Lee, cant e-mail you yet until i'm an 'upgraded' member !
Just like to thank you for your advice with my SRX3801. Two soft output devices replaced and the amp has stopped overheating.
With only about 5mV across the gate resistors this was not enough to bring the protect in, hence throwinig me a little.
In the past with the many XR and RA amps we have used for PA work the 2SJ and 2SK devices seem to fail and bring in the protect circuit immediately and then the light bulb trick sorts the down time out pretty quickly.
Hope the new modular amps and powered speakers are going well for you and keep up the posts on here as your advice is of great help to a many of us.
Hi Lee,
I'm finally back in the workshop with this naughty RA3000.
To Refresh you, this one seems to be slew rate limiting.
Both channels behave identically 80V and 100V rails are good.
feeding with a 100Hz sine wave i get full amplitude sine wave out of it (with or without load).
As I increase the frequency, the response rolls off at about 200Hz !
If I increase the signal amplitude, I get a near perfect Triangle suggesting there is some integration going on somewhere.
Last time I was in the amp, I replaced a few of the small electrolytics (suspecting the C56/R98 filter on the feedback line). I also replaced C54/C60 and C55 while i was in there for no real reason except that they might've dried out.
I have tested the signal between the level pots / Input buffer, and the fault is definately somewhere after that.
Any ideas ?
regards,
jonathan
I'm finally back in the workshop with this naughty RA3000.
To Refresh you, this one seems to be slew rate limiting.
Both channels behave identically 80V and 100V rails are good.
feeding with a 100Hz sine wave i get full amplitude sine wave out of it (with or without load).
As I increase the frequency, the response rolls off at about 200Hz !
If I increase the signal amplitude, I get a near perfect Triangle suggesting there is some integration going on somewhere.
Last time I was in the amp, I replaced a few of the small electrolytics (suspecting the C56/R98 filter on the feedback line). I also replaced C54/C60 and C55 while i was in there for no real reason except that they might've dried out.
I have tested the signal between the level pots / Input buffer, and the fault is definately somewhere after that.
Any ideas ?
regards,
jonathan
yeah - i haven't tried calling him because i guess he must be busy - i've got this ra-3 with a bizzare fault.
just out of interest, what problems are you having with your TR ?
i think one of the revisions was the addition of a resistor in the base of each output device... but we're talking about 15 years ago.
j
just out of interest, what problems are you having with your TR ?
i think one of the revisions was the addition of a resistor in the base of each output device... but we're talking about 15 years ago.
j
First of all there's a few non-matched output transistors fitted from a previous repair. One channel appears heavily repaired and has a 200mV output offset compared to the working side, the offset pot runs out of room before it's gone below 150mV. Secondly, when you put it into standby (a dedicated switch) the relays drop out then after a few seconds start to buzz, getting louder till eventually they come back in again! The standby circuit has had alot of components changed and bits bodged in here and there by the phantom dabbler.
Wow ! - I hate it when they let the monkeys play with the goods !
sometimes... and i only do this with my own stock (not customer's amps), I completely strip an amp down and turn it into a 'kit', removing all transistors, and one end of all diodes. This leaves an RC network on the PCB which can be meter-tested.
then i test the transistors off board, and re-build the amp.
very time consuming... did you know an EV P1200 has over 100 transistors ?
haha !
In your case, i'd definately test all the output devices out off the board.
and i'd pull the bias ladder apart and test the components off board too.
I'm not due back to my workshop for a few weeks, but i'll dig out the schematics for you if it helps.
The ones we had seemed to have a badly designed thermal control system... even if the amps were idling, the multicolour LED would cycle through green-red-green - often within a 10 second period - the cooling fans ramped up and down accordingly.
sometimes... and i only do this with my own stock (not customer's amps), I completely strip an amp down and turn it into a 'kit', removing all transistors, and one end of all diodes. This leaves an RC network on the PCB which can be meter-tested.
then i test the transistors off board, and re-build the amp.
very time consuming... did you know an EV P1200 has over 100 transistors ?
haha !
In your case, i'd definately test all the output devices out off the board.
and i'd pull the bias ladder apart and test the components off board too.
I'm not due back to my workshop for a few weeks, but i'll dig out the schematics for you if it helps.
The ones we had seemed to have a badly designed thermal control system... even if the amps were idling, the multicolour LED would cycle through green-red-green - often within a 10 second period - the cooling fans ramped up and down accordingly.
Dear sir, please forgive me for interupting in this discussion, only I too have an RA3000 which I aquired with the softstart circuit disconnected also the LED boards missing. The amp works fine on both channels but I would like to re-connect the softstart circuit. I am reading these posts to find a solution to my amp shortcommings. Please could anyone help with a sketch of the softstart circuit sent to me?
Noizyboy
Noizyboy
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