I have been working on this Luxman C1000 preamp.
It actually worked fine for 20 mins and then started rapidly clicking the relay on and off rapidly.
The circuit board with that relay is attached.
I am getting 48 v AC at the 2 coil prongs on the relay. I should get DC only, no AC there.
They are fed from the power supply right after the bridge rectifier.
What could be happening in this.
Thanks.
Srinath.
It actually worked fine for 20 mins and then started rapidly clicking the relay on and off rapidly.
The circuit board with that relay is attached.
I am getting 48 v AC at the 2 coil prongs on the relay. I should get DC only, no AC there.
They are fed from the power supply right after the bridge rectifier.
What could be happening in this.
Thanks.
Srinath.
Attachments
How do you know you are getting AC ? A DVM reading isn't proof of AC if that is what you are using. Many DVM's show a voltage reading on AC ranges even when connected to DC.
If you isolate that "804" connection (or at least prove its not that going high and turning the relay off) then favourites would be one of the rectifiers going open circuit, a dodgy reservoir cap or the relay drive transistor going intermittent open circuit.
If you isolate that "804" connection (or at least prove its not that going high and turning the relay off) then favourites would be one of the rectifiers going open circuit, a dodgy reservoir cap or the relay drive transistor going intermittent open circuit.
I am reading AC, and no dc. Yea I know the DMM can read dc for ac and ac in a dc circuit.
804 goes to the winker board - the winker board also get a 12v dc from another connection into it. You're saying 804 is likely to be getting a higher voltage than what its intended to from the winker - I'll post that board 1 sec.
It goes to 703, and 702 is 12V DC from the powersupply.
Thanks.
Srinath.
Attachments
It was a possibility it could be getting a higher voltage but having seen the circuit... no 🙂
If the fault is intermittent then I would just change the parts I mentioned above as a first step (and check the whole PCB for dries). If its still faulty after that then go for the other semiconductors and the 10uf cap at the left.
I know its an unscientific way of fixing it but when things are intermittent it can be the best approach.
To actually find the fault you need to monitor the supply and the base drive to the relay driver transistor to see where the problem lies... is the transistor being told to turn off or is it just going open circuit intermittently.
If the fault is intermittent then I would just change the parts I mentioned above as a first step (and check the whole PCB for dries). If its still faulty after that then go for the other semiconductors and the 10uf cap at the left.
I know its an unscientific way of fixing it but when things are intermittent it can be the best approach.
To actually find the fault you need to monitor the supply and the base drive to the relay driver transistor to see where the problem lies... is the transistor being told to turn off or is it just going open circuit intermittently.
Not intermittent at all ... the relay always flutters ... 60 hz or 120 hz is what I am not sure ...
10 uf cap ... first try, why, its the easiest he he ... and I have a nice shiny new cap to put in there.
Its like my method of "trouble shooting" - remove parts 1 at a time till something changes.
Cool.
Srinath.
10 uf cap ... first try, why, its the easiest he he ... and I have a nice shiny new cap to put in there.
Its like my method of "trouble shooting" - remove parts 1 at a time till something changes.
Cool.
Srinath.
If the relay flutters, then id go with Mooly, and check the rectifier diodes first. Also the fly back diode (if there is one, cant see pic on my mobile....)
Then caps after, if no improvement.
Then caps after, if no improvement.
Lol, i managed to get the schematic big enough for me to read... Lots of diodes there! I thought most were resistors!
Good luck! Id listen to Mooly, and ignore me lol...i must be getting old, time to go to the optician ��
Good luck! Id listen to Mooly, and ignore me lol...i must be getting old, time to go to the optician ��
C803 swapped with a 50v 68uf (only had that on hand) and I got 27 v DC @ the relay.
Not touched 801 yet.
Cool.
Srinath.
Not touched 801 yet.
Cool.
Srinath.
That's good 🙂
The cap value is important because it will partly determine the drop out time of the relay.
The cap value is important because it will partly determine the drop out time of the relay.
From 22uf 50v, I put a 68uf 50v. Is that likely to cause another problem.
It seems to turn itself on in about the same time frame as it fluttered that relay before.
Cool.
Srinath.
It seems to turn itself on in about the same time frame as it fluttered that relay before.
Cool.
Srinath.
That is no problem, it seems to be about the same time as the usual amp/preamp speaker protect relay.
Thanks so much.
Cool.
Srinath.
Thanks so much.
Cool.
Srinath.
This pre amp now works perfectly, or like it did in the first 20 mins I owned it ... but the balance seems to have very little effect.
Like when I flip it left, the left channel is working, but the right channel it still making sound, it only drops maybe 3 db, or even less. Same with right too.
Is that called channel separation ? If so, I dont have much separation ...
I will open it and check for what's in there to change ...
Cool.
Srinath.
Like when I flip it left, the left channel is working, but the right channel it still making sound, it only drops maybe 3 db, or even less. Same with right too.
Is that called channel separation ? If so, I dont have much separation ...
I will open it and check for what's in there to change ...
Cool.
Srinath.
Probably normal and as designed. Usually the balance control is only needed for fine adjustment. You would have to study the circuit to see how it could be altered, probably by shorting or lowering a couple of resistors.
Yea I would guess so, there is 3000 components in this thing, I am not going in there fishing with a soldering iron. Its a miracle I got out of that thing without burning something. Thanks mooly.
Cool.
Srinath.
Cool.
Srinath.
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