My Sugden Masterclass IA-4 made a smokeshow today... Schematic would definitely help to repair it.
Thanks
Thanks
I have found a burned 10 ohm 1/4 watt carbon resistor labeled R33 on the right channel amplifier board.
What should i check before replacing this resistor?
What should i check before replacing this resistor?
Im removing all the diode and transistor to test them, i have not finished but for now they are all good. Nothing seem damaged except the 10ohm resistor. I think i will replace this resistor and try to power up the amplifier.
But before can someone help me on how to adjust the bias.
* the output transistor are Sanken 2SC2922
But before can someone help me on how to adjust the bias.
* the output transistor are Sanken 2SC2922
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Without circuits your only guide is the good channel. If the amp powers up I would measure and record the current in the good channel, then if possible set it (or force by overiding any vbe generator) to zero. Perform the same procedure on the bad channel (set to zero bias) and then use a bulb tester to power the amp. Hopefully that will allow you to work on it. Unless you reduce the bias the Class A biasing makes use of a bulb tester impossible.
You could always try an email to Sugden asking if there is a known issue for this. I asked them about a lockup problem on the latest CD21SE when CDRW's were inserted and they kindly sent me details of a resistor change on the servo PCB together with photos.
You could always try an email to Sugden asking if there is a known issue for this. I asked them about a lockup problem on the latest CD21SE when CDRW's were inserted and they kindly sent me details of a resistor change on the servo PCB together with photos.
I have replaced the resistor and powered the amp, everything seem to be normal. I didnt touched the bias adjustement on the bad channel so it is like it was before.
Like you sugested me i will check the good side and try to adjust the bad channel to the same.
I already Emailed Sugden about this issue, since the amp is still under warranty. I will try to get all the missing iformations with them.
Thanks,
Like you sugested me i will check the good side and try to adjust the bad channel to the same.
I already Emailed Sugden about this issue, since the amp is still under warranty. I will try to get all the missing iformations with them.
Thanks,
That sounds promising.
Have a measure at the volt drop across these resistors and compare left and right. How close to the resistors dissipation rating is it.
Have a measure at the volt drop across these resistors and compare left and right. How close to the resistors dissipation rating is it.
I have took the current from the fuse after I let the amplifier get to normal temperature of operation. On the good side and it showed 1.4A, so i have checked the repaired side the same way and it was at 1.42A so I have adjusted it to 1.4A like the good side.
I dont know if its the good way to do it, but im sure it's pretty close.
The IA-4 played beautifull music for a full 8h with no issue.
I dont know if its the good way to do it, but im sure it's pretty close.
The IA-4 played beautifull music for a full 8h with no issue.
Pleased it's working OK. It's worth measuring the volt across that resistor (on both channels) though. 1/4w at 10Ω means no more than around 1.5 volts dc and preferably less for long term reliability.
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