Hi all,
I have had this amp 10 years now, it's been sitting in storage until I had time to change out the caps and do all the ECO's, which are now done, but the damn thing won't start now and I am working my way thru the schematics and just can't figure out why. Yes it was working 10 years ago when parked.
There may be a startup sequence I am not familiar with, so it could be just me, but I have read the manual and I am just not getting any LED light up on the front panel, nor LED100 or LED101 on the VSMB board. I have confirmed I'm getting power to VSMB board and VR1 and VR12 are working, there are voltages all around the board, but when I push the main power button on the front, nothing, no change, no current draw...nothing. Is there some sort of time delay? Manual says nothing about holding in the power button to turn on, only off.
Any thoughts?
Would appreciate some help from someone who knows the 300 series please and thanks.
Cheers
I have had this amp 10 years now, it's been sitting in storage until I had time to change out the caps and do all the ECO's, which are now done, but the damn thing won't start now and I am working my way thru the schematics and just can't figure out why. Yes it was working 10 years ago when parked.
There may be a startup sequence I am not familiar with, so it could be just me, but I have read the manual and I am just not getting any LED light up on the front panel, nor LED100 or LED101 on the VSMB board. I have confirmed I'm getting power to VSMB board and VR1 and VR12 are working, there are voltages all around the board, but when I push the main power button on the front, nothing, no change, no current draw...nothing. Is there some sort of time delay? Manual says nothing about holding in the power button to turn on, only off.
Any thoughts?
Would appreciate some help from someone who knows the 300 series please and thanks.
Cheers
Well it's fixed! Yeah!
A bit of intense troubleshooting, but I found there is a onboard smart monitor chip which monitors all major parameters and shuts down the amp if any one of them is out of normal range, there is a chart in the service manual that shows all the states of the pins, and it turns out that there was a "fault", in that it thought there was an over temp situation and it wouldn't start. I found a cold solder joint on the current regulator board on one of the series connected thermal switches, reflowed the joint and put it all back together (getting pretty good at it now, it's been apart 3 or 4 times in the last week
) and it fired right up, zero DC offset, all voltages look good, so now it just needs to warm up for a couple of hours and I can go thru all the adjustments to make sure bias etc is all up to spec.
And Pyramid said it was a very difficult amp to troubleshoot and I should send it in and pay whatever the exorbitant fee was (he never did tell me) ...well poop on them I say. It had a DC offset when I bought it and one of the regulators for the +/-115 was off, found 2 little TO-92s on the current regulator board that had faults, a 2N5401 and MPSA64, replaced those and that's all it was.
I may post a thread in the next few days for the 300 series with tips and tricks that I have learned along the way, hoping that it may help someone else one day. It's a complex amp...looking forward to hearing it finally after 10 years of it sitting in the closet.
Cheers
A bit of intense troubleshooting, but I found there is a onboard smart monitor chip which monitors all major parameters and shuts down the amp if any one of them is out of normal range, there is a chart in the service manual that shows all the states of the pins, and it turns out that there was a "fault", in that it thought there was an over temp situation and it wouldn't start. I found a cold solder joint on the current regulator board on one of the series connected thermal switches, reflowed the joint and put it all back together (getting pretty good at it now, it's been apart 3 or 4 times in the last week
) and it fired right up, zero DC offset, all voltages look good, so now it just needs to warm up for a couple of hours and I can go thru all the adjustments to make sure bias etc is all up to spec. And Pyramid said it was a very difficult amp to troubleshoot and I should send it in and pay whatever the exorbitant fee was (he never did tell me) ...well poop on them I say. It had a DC offset when I bought it and one of the regulators for the +/-115 was off, found 2 little TO-92s on the current regulator board that had faults, a 2N5401 and MPSA64, replaced those and that's all it was.
I may post a thread in the next few days for the 300 series with tips and tricks that I have learned along the way, hoping that it may help someone else one day. It's a complex amp...looking forward to hearing it finally after 10 years of it sitting in the closet.
Cheers
With a bit of logical thinking and working through the amp the fault can often be found.
Breaking it down into sections and working on them makes the job easier.
I bought in a none working Maplin amplifier.
It powered up and made sound but horribly distorted.
I checked every single component on the pcb and they all checked fine.
However I kept coming back to one transistor where the voltages didnt seem quite
right. It diode checked OK. Then it hit me the diode check was wrong way around. Someone had fitted a NPN instead of PNP. Unluckily for me the transistor number had worn off. So after a struggle finding old transistor I found one on ebay, fitted it and amp works fine now.
Its hard enough finding faults without wrong components fitted.
I built up a couple of power amps from my own design.
None worked. Checked my design and nothing special or untoward there.
So out with meter and checked every component.
I found 10k resistor where a 1k one should be.
Checked the component bag and hey presto marked as 1k with 10k resistors in the bag.
So on the phone to Farnell to give them a telling off.
All they did was thank me for letting them know and promised to send out right component next day. That didnt pay for my time debugging the faulty pcb's or time replacing wrong resistors.
Breaking it down into sections and working on them makes the job easier.
I bought in a none working Maplin amplifier.
It powered up and made sound but horribly distorted.
I checked every single component on the pcb and they all checked fine.
However I kept coming back to one transistor where the voltages didnt seem quite
right. It diode checked OK. Then it hit me the diode check was wrong way around. Someone had fitted a NPN instead of PNP. Unluckily for me the transistor number had worn off. So after a struggle finding old transistor I found one on ebay, fitted it and amp works fine now.
Its hard enough finding faults without wrong components fitted.
I built up a couple of power amps from my own design.
None worked. Checked my design and nothing special or untoward there.
So out with meter and checked every component.
I found 10k resistor where a 1k one should be.
Checked the component bag and hey presto marked as 1k with 10k resistors in the bag.
So on the phone to Farnell to give them a telling off.
All they did was thank me for letting them know and promised to send out right component next day. That didnt pay for my time debugging the faulty pcb's or time replacing wrong resistors.
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