Hi, I am working on ONKYO TX-SR707 for Protection Mode issue and SBL channel failure, as Power AMP transistors repeatedly blows off. Have done most of the channel related resitors , transistors and Caps replacement as suggestted by someone in DIY audio, but now I am stuck on the Current Idling of the SBL Channel,
I dont want to take another chance of amp getting failled again as I have tested it and found powering on for few seconds but goes back into protection mode and heats up too much.
As I googled someone has suggested to go for readjustment of Idling current but couldn't got the details as how much current for each channel should have for this specific model.
Can anybody help me how much is the Idling current for each Channel for the specific model of TX-SR707 MMP/MMO/MMA/MMQ?
Please ignore grammar mistakes as my english is not very good enough.
Thanks is advance.
I dont want to take another chance of amp getting failled again as I have tested it and found powering on for few seconds but goes back into protection mode and heats up too much.
As I googled someone has suggested to go for readjustment of Idling current but couldn't got the details as how much current for each channel should have for this specific model.
Can anybody help me how much is the Idling current for each Channel for the specific model of TX-SR707 MMP/MMO/MMA/MMQ?
Please ignore grammar mistakes as my english is not very good enough.
Thanks is advance.
I would start off with 10mA and see if it still over heats.
If it does there is still a problem elsewhere.
If it does there is still a problem elsewhere.
Take your cue for bias adj setting from all the others (as an average ignoring the channel you're repairing)
Be warned when the main output devices blow on these models , they do a lot of collateral damage on the pre-driver daughter board, you need to meticulously check every single stood off resistor on there , and you'll find several semi's damaged there too. The resistors once damaged can blow fully O/C or they can drift off value... you have many other good channels to compare with.
Properly repaired the bias should be the same as the other channels (with the adj pot is pretty much the exact same position as the others), if it's off postion to get that same bias you've obviously not repaired it fully
Be warned when the main output devices blow on these models , they do a lot of collateral damage on the pre-driver daughter board, you need to meticulously check every single stood off resistor on there , and you'll find several semi's damaged there too. The resistors once damaged can blow fully O/C or they can drift off value... you have many other good channels to compare with.
Properly repaired the bias should be the same as the other channels (with the adj pot is pretty much the exact same position as the others), if it's off postion to get that same bias you've obviously not repaired it fully
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Hi thanks for the respose will try to start with 10mA, however amp currently is down with wirewound resistor failure "MPR5W+5W 0R22" and I am trying to arrange it.
@ MikePP have few querries as you quoted :
" Take your cue for bias adj setting from all the others (as an average ignoring the channel you're repairing)" - Dose it mean average idling will be almost same for rest of all the channels? Please clarify as I dont have indepth knowledge in bias adjustment idling.
" Be warned when the main output devices blow on these models , they do a lot of collateral damage on the pre-driver daughter board...."
Yes I have throughly checked each and every component in the specific channel with the help of digital multimeter and compared them with the same components placed in other good channels, every thing seems to be quite good and 99.99% have same readings in pre-driver daughter board.
Though there were 1-2 resistor and transitor failure in output section, which I have replaced now with the equivivalent components, except the one wire wound resistor "MPR5W+5W 0R22" placed at "R6106" as per schematics(found very high resistance on one side of the resitor where in the other side is fine as compared with similar resistors used for other channels. (I found it failed when I tried to restart the amp and kept it on for longer time and the amp came back in standby mode. But for my luck it haven't imapcted any other components in the channel)
Actually I havent touched or disturbed any of the Bais adj. yet since the time of its first failure other than just replacing the failled components. I was just wondering if these couple of failures have caused any impact on the bais adj (this is the reason for my query on idling as it was suspected that other components failed in 1-2 stages of repair when I replaced the transistor Q6106 and Q6116, as most of the components are older ones and the replacement is done only for the component (with equal values ) that has failed. Has this creatred any inbalance in the idling adj or the circuit?
@ MikePP have few querries as you quoted :
" Take your cue for bias adj setting from all the others (as an average ignoring the channel you're repairing)" - Dose it mean average idling will be almost same for rest of all the channels? Please clarify as I dont have indepth knowledge in bias adjustment idling.
" Be warned when the main output devices blow on these models , they do a lot of collateral damage on the pre-driver daughter board...."
Yes I have throughly checked each and every component in the specific channel with the help of digital multimeter and compared them with the same components placed in other good channels, every thing seems to be quite good and 99.99% have same readings in pre-driver daughter board.
Though there were 1-2 resistor and transitor failure in output section, which I have replaced now with the equivivalent components, except the one wire wound resistor "MPR5W+5W 0R22" placed at "R6106" as per schematics(found very high resistance on one side of the resitor where in the other side is fine as compared with similar resistors used for other channels. (I found it failed when I tried to restart the amp and kept it on for longer time and the amp came back in standby mode. But for my luck it haven't imapcted any other components in the channel)
Actually I havent touched or disturbed any of the Bais adj. yet since the time of its first failure other than just replacing the failled components. I was just wondering if these couple of failures have caused any impact on the bais adj (this is the reason for my query on idling as it was suspected that other components failed in 1-2 stages of repair when I replaced the transistor Q6106 and Q6116, as most of the components are older ones and the replacement is done only for the component (with equal values ) that has failed. Has this creatred any inbalance in the idling adj or the circuit?
The plate resistor combo is very common to fail when the output devices... it's usually a given that's blown either (or both) sides.
What I meant by collateral damage is resistors like the 120r, 82r, 22r, 18r, and 10rs in the pre-driver for that channel and all those small signal semi's in the same area.
Once you have caught every failed component (and used genuine semi's for replacement, the bias setting postion should be no different to any of the untouched channels (you can see they'll all be at (for instance) the 1oclock position or whatever, if your repaired channel adj pot position is much different to those (to achieve the bias value they have) you've not caught all the damaged components.
With genuine semi's you often just end up comfirming the bias is back to normal without any further adj. I usually run these up on a twin DC current limited bench supply to check before throwing it all back together and putting the mains on
What I meant by collateral damage is resistors like the 120r, 82r, 22r, 18r, and 10rs in the pre-driver for that channel and all those small signal semi's in the same area.
Once you have caught every failed component (and used genuine semi's for replacement, the bias setting postion should be no different to any of the untouched channels (you can see they'll all be at (for instance) the 1oclock position or whatever, if your repaired channel adj pot position is much different to those (to achieve the bias value they have) you've not caught all the damaged components.
With genuine semi's you often just end up comfirming the bias is back to normal without any further adj. I usually run these up on a twin DC current limited bench supply to check before throwing it all back together and putting the mains on
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