Sony DA3300ES T6.24l 250v fuse keep blowing

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Amosika

Joined Oct 6, 2021
13
Hi,I have this old sony DA3300ES AVR which I use for my computer. Last Monday the sound just cut out while playing but there was no protection or power off. I did checked connections and speaks but still no sound. I even did hard rest but still the same. It turned on fine and speakers indicators also shows on the screen and the hear the click noise when I turn on the avr. Today I opened it up and saw that all 4 of the T6.24l 250v fuse were blown. I replaced them to see why and the first 2 immediately blown again after powering. What could be the issue because I tested the main diode connected to the fuse and it seems ok. Please what else could lead to this?
 

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Thread Starter

Amosika

Joined Oct 6, 2021
13
Do you have a schematic?
Did you test the other bridge rectifier?
Yes. When its placed on the board both P(+) and N(-) are opened and beeps when tested but when I take it out of the board only the P is opened but the N is still closed. I tested the ohmns resistor there and its fine. Is it that the rectifier is bad or what? But the other rectifier on the other side seems fine because when its on the board only the P is opened and N is closed. What could be the issue here.
 

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Amosika

Joined Oct 6, 2021
13
Do you have a schematic?
Did you test the other bridge rectifier?
This is the reading I got for the rectifier.
When I put the position leads to the Negative and test the AC outlets I get no reads at all either on both sides( same as negative to positive) but when I put positive to positive,I get readings on both AC and the same as negative yo Negative I get readings on both AC. Does it means the rectifier is bad?
 

AlbertHall

Joined Jun 4, 2014
11,594
These fuses are in the UK version (not the USA version) and are just before the bridge rectifiers. Since all 4 blow, it would suggest a drastic failure of both rectifiers.
Or a short circuit following the rectifiers, possibly the reservoir capacitors after the rectifiers.
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
Or a short circuit following the rectifiers, possibly the reservoir capacitors after the rectifiers.
I tested the bridge rectifier and they were good. So what I did was to insect new fuse and disconnect the power that goes to Amp board. After I disconnected it,the fuse never blown. So meaning some of the Darlington are shot. But it seems the readings are different from normal transistors. How do I test it.
 

AlbertHall

Joined Jun 4, 2014
11,594
As you are looking for a shorted device you need to test collector to emitter and collector to base.
The bit that is different for a darlington is emiiter to base so you don't need to worry about that bit.
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
As you are looking for a shorted device you need to test collector to emitter and collector to base.
The bit that is different for a darlington is emiiter to base so you don't need to worry about that bit.
Thank you very much guys for your help. I detected that the surround back left channel was the problem. The pair Darlington were blown and opened. I've taken them out and now the avr is stable and working fine. I will order a new one to replace them next week . thanks for your time
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
As you are looking for a shorted device you need to test collector to emitter and collector to base.
The bit that is different for a darlington is emiiter to base so you don't need to worry about that bit.
Its weird. After taking the transistors off I still get the fuse blown again after couple of minutes. I checked again and all Darlington seems good but still it keeps blowing fuse. Is it because of the 2 unreplaced transistors needs to be replaced? Bridge is good and the remaining transistors are also good according to the readings. What's wrong now?
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
I checked this morning and I have both surround back Darlington damaged and also left front channel. How did that happened? All my speakers are working fine and I have no leak wires or something. Also the speakers are new energy speakers I bought for my new Harman Kardon AV 3700. But now it has been stable for a while. I will make an order to replace these resistors but before I want to know if there are somethings I need to check before replacement?
 

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abrsvc

Joined Jun 16, 2018
97
I would start looking at the protector board for problems there. There are voltages present and conditions that are causing these components to short. Whether or not the protection circuit can detect these is up to debate, but there is a fault somewhere that you are not seeing. Measure the voltages on the pads of the removed transistors and post those here. That may provide a clue. Unlike older designs, this unit does not use a voltage amp IC. Check the pre-driver circuits as well (page 54 of the service manual)
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
I would start looking at the protector board for problems there. There are voltages present and conditions that are causing these components to short. Whether or not the protection circuit can detect these is up to debate, but there is a fault somewhere that you are not seeing. Measure the voltages on the pads of the removed transistors and post those here. That may provide a clue. Unlike older designs, this unit does not use a voltage amp IC. Check the pre-driver circuits as well (page 54 of the service manual)
Alright sir,I will take some time tomorrow and check them to see if there is a leak voltage or over voltage somewhere that caused these six transistors to damage before replacement,then post the results here. Thank you for suggestions.
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
I would start looking at the protector board for problems there. There are voltages present and conditions that are causing these components to short. Whether or not the protection circuit can detect these is up to debate, but there is a fault somewhere that you are not seeing. Measure the voltages on the pads of the removed transistors and post those here. That may provide a clue. Unlike older designs, this unit does not use a voltage amp IC. Check the pre-driver circuits as well (page 54 of the service manual)
I don't know how it happened but after several checked up,I got 2 swelling capacitors on tge surround back A class Amp board section and also got this dead transistor on the BIAS board. I think these must be causing the issue. Aside these everything is good I don't know if this fead transistor can affect a JRC ic it was linked to but I checked up a zina diode that was also linked to it and it was good. Is it advisable to change the ic too? How to I check for a bad ic? I will appreciate your help
 

Thread Starter

Amosika

Joined Oct 6, 2021
13
I would start looking at the protector board for problems there. There are voltages present and conditions that are causing these components to short. Whether or not the protection circuit can detect these is up to debate, but there is a fault somewhere that you are not seeing. Measure the voltages on the pads of the removed transistors and post those here. That may provide a clue. Unlike older designs, this unit does not use a voltage amp IC. Check the pre-driver circuits as well (page 54 of the service manual)
 

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Thread Starter

Amosika

Joined Oct 6, 2021
13
I continued to dig further and found out that a whole bunch of c124 transistors are dead. I tested them out and they're about 6 of them on the Aclass board and one on the BIAS board which don't read at all at any ohmns on and off the board. What could be the possible reason? Also I tested the JRC 4565D ice and the out put is 1095 but the rest of the legs stay btn 600-700. Are they good? I suspect those 2 ic to be the issue killing those transistors
 

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