ok i managed to stop the amp from going into protect after 3 seconds, it seems there was a short on one of the pin wires going to one the the pcbs,
i have set bias to a low 9.0mv
the amp has been on for 30mins and still on so far, , but ive noticed "sometimes" i just switches itself off after 20-45 mins for no apparent reason?
another thing on the main pcb theres a part which says "fan test short" so does this mean if i bridge the 2 together then i would be able to keep the fan running constently?
shown in pic below.
ive noticed theres athermal sensor which attaches to the heatsink which monitors the heatsink temp, and im thinking it might be faulty as i have applyed some fake heat and the fans dont kick in.
i have set bias to a low 9.0mv
the amp has been on for 30mins and still on so far, , but ive noticed "sometimes" i just switches itself off after 20-45 mins for no apparent reason?
another thing on the main pcb theres a part which says "fan test short" so does this mean if i bridge the 2 together then i would be able to keep the fan running constently?
shown in pic below.
ive noticed theres athermal sensor which attaches to the heatsink which monitors the heatsink temp, and im thinking it might be faulty as i have applyed some fake heat and the fans dont kick in.
hi chris,
dont seem to get the protect error anymore,
i do however have trouble switching the amp on? most times it will stop in standby and when it does come on it stops on for about 2 secs then straight off again?
i dont see a protect error and also i even removed fuses & dissconnected the 2 power blocks for the amplifier section, so any ideas why i refuses to come out of standy and when it does goes back off again a few seconds later?
its puzzling me? you come across this problem before mate?
dont seem to get the protect error anymore,
i do however have trouble switching the amp on? most times it will stop in standby and when it does come on it stops on for about 2 secs then straight off again?
i dont see a protect error and also i even removed fuses & dissconnected the 2 power blocks for the amplifier section, so any ideas why i refuses to come out of standy and when it does goes back off again a few seconds later?
its puzzling me? you come across this problem before mate?
Hi mrlennon,
It's possible the unit does not like the amps not plugged in. Floating protect line.
Check the over current protection transistors, pull them from the channel that was blown and test briefly. Sometimes they can become leaky and give a false trip. And yes, I've had to troubleshoot defective protection circuits many times before.
-Chris
It's possible the unit does not like the amps not plugged in. Floating protect line.
Check the over current protection transistors, pull them from the channel that was blown and test briefly. Sometimes they can become leaky and give a false trip. And yes, I've had to troubleshoot defective protection circuits many times before.
-Chris
ok i checked the transistors and they check out ok?
can i ask how you test a ic regulator with my dmm? (KA7805-ABTU) same as a transistor? base,collector, immitter ?
what else do u think it could be chris? its seems very very hard to get this unit out of standby,
i have only had success by pressing the reset button on the transformer and then pressing the tone button to reset the amp, however this dont work all the time however when it does come on it goes straight back off after 1 -2 seconds?
im pretty sure its not the amplifier section? so what do u think would cause this? as it never had this problem before.
thanks.
can i ask how you test a ic regulator with my dmm? (KA7805-ABTU) same as a transistor? base,collector, immitter ?
what else do u think it could be chris? its seems very very hard to get this unit out of standby,
i have only had success by pressing the reset button on the transformer and then pressing the tone button to reset the amp, however this dont work all the time however when it does come on it goes straight back off after 1 -2 seconds?
im pretty sure its not the amplifier section? so what do u think would cause this? as it never had this problem before.
thanks.
Hi mrlennon,
The regulator is best just measured in circuit. About 5V output, you can not measure it like a transistor. It's an entire circuit in there.
At this point I normally attack your problem in a different way. I do not recommend you do the same. I have different tools to use where you really don't.
In essence, you need to find out what is tripping the unit off. All you can do is monitor a test point as you turn the unit on. I would force the unit on at partial voltage using a variac and "test methods". Don't even consider doing this. It's very risky if you are not an experienced tech.
So look at the schematic and follow the different protection circuits. Find out which is causing your grief.
-Chris
The regulator is best just measured in circuit. About 5V output, you can not measure it like a transistor. It's an entire circuit in there.
At this point I normally attack your problem in a different way. I do not recommend you do the same. I have different tools to use where you really don't.
In essence, you need to find out what is tripping the unit off. All you can do is monitor a test point as you turn the unit on. I would force the unit on at partial voltage using a variac and "test methods". Don't even consider doing this. It's very risky if you are not an experienced tech.
So look at the schematic and follow the different protection circuits. Find out which is causing your grief.
-Chris
Still no luck ?
Can you make a picture of the whole board ?
1) I do not believe the protection switch off whole amp.
Maybe it does...
Usually there shall be a relais per channel that separates the amp out from the speaker output connectors on the rear plate.
That means you need to find out if you have DC offset on one output.
Please look for white ceramic resistors, or maybe other color about 0,33 ohm or so, a pair per channel ( emitter resistors ), and measure if there is about a few mV to ground if the amp is on.
If it is more than 1V DC or so, protection will be active.
2) Measure outputs of all 7805 regulators, 5V there ?
3) Control solder joints , better resolder all regulators, they usually become hot and desolder themselves, usually very little tin there and no heat sinks, this is expensive stuff you know...
4) Switch the amp on and touch transistors, compare felt temperature of same parts in different channels, something gets hot ? . DO NOT touch AC line of course....
5) Measure the current draws of each + and - rail supply, they all should be about same value. Need to find a way to disconnect supply and put the ampere meter there.
6) If the protection switches off the whole amp, separate the channel outputs from the protection one after another untile it does stay on. Do not connect speakers, they may blow... Perhaps connect open protection inputs to ground.
7) If all does not help, remove all output transistors of each channel, one channel after another, switch on and see if protection is still active.
8) Did you check all parts in protection circuit ?
9) IMHO you have only 3 possibilities:
* the protection itself is faulty, I do not think so, because you already have found a bad channel.
* You still have one blown output transistor that causes rail voltage to be present on the output, so protection is active with good reason.
* You have two blown transistors in a channel causing a short between rails.
10) Anyway, if you check all parts, you must find a bad one.
Blown ( open ) emitter resistor ?
Can you make a picture of the whole board ?
1) I do not believe the protection switch off whole amp.
Maybe it does...
Usually there shall be a relais per channel that separates the amp out from the speaker output connectors on the rear plate.
That means you need to find out if you have DC offset on one output.
Please look for white ceramic resistors, or maybe other color about 0,33 ohm or so, a pair per channel ( emitter resistors ), and measure if there is about a few mV to ground if the amp is on.
If it is more than 1V DC or so, protection will be active.
2) Measure outputs of all 7805 regulators, 5V there ?
3) Control solder joints , better resolder all regulators, they usually become hot and desolder themselves, usually very little tin there and no heat sinks, this is expensive stuff you know...
4) Switch the amp on and touch transistors, compare felt temperature of same parts in different channels, something gets hot ? . DO NOT touch AC line of course....
5) Measure the current draws of each + and - rail supply, they all should be about same value. Need to find a way to disconnect supply and put the ampere meter there.
6) If the protection switches off the whole amp, separate the channel outputs from the protection one after another untile it does stay on. Do not connect speakers, they may blow... Perhaps connect open protection inputs to ground.
7) If all does not help, remove all output transistors of each channel, one channel after another, switch on and see if protection is still active.
8) Did you check all parts in protection circuit ?
9) IMHO you have only 3 possibilities:
* the protection itself is faulty, I do not think so, because you already have found a bad channel.
* You still have one blown output transistor that causes rail voltage to be present on the output, so protection is active with good reason.
* You have two blown transistors in a channel causing a short between rails.
10) Anyway, if you check all parts, you must find a bad one.
Blown ( open ) emitter resistor ?
Hi Bernhard,
The amplifier will sometimes stay on, therefore there is no permanent defect in any output amplifier stage.
Protection circuits will disconnect all amplifiers, and in this case, power the unit off. It is possible to have a leaky transistor in the offset or current detect circuits. It will test fine with a normal meter. Substitution is the only easy way to locate this defect unless the amplifier can be forced into the on state. Not recommended in this case.
The defective channel has been repaired. It is entirely possible there is a power supply fault. So unfortunately, there are many possibilities. Troubleshooting protection circuits can be an arduous task.
-Chris
The amplifier will sometimes stay on, therefore there is no permanent defect in any output amplifier stage.
Protection circuits will disconnect all amplifiers, and in this case, power the unit off. It is possible to have a leaky transistor in the offset or current detect circuits. It will test fine with a normal meter. Substitution is the only easy way to locate this defect unless the amplifier can be forced into the on state. Not recommended in this case.
The defective channel has been repaired. It is entirely possible there is a power supply fault. So unfortunately, there are many possibilities. Troubleshooting protection circuits can be an arduous task.
-Chris
ok just a update im really thinking of changing the ic regulator as im thinking it might be that, i cant get to measure it as its consealed behind to elec capacitors,
if the ic regulator is leaky them im sure it would cause it to stop in standby most of the time, ( 1 sec them back off) well i cant only try and change it least it will rule out the possibility of a faulty ic regulator,
ok the part number is HVIMC7805C, 2nd part number is: KA7805-ABTU.
will this one be ok as a replacment http://www.maplin.co.uk/Search.aspx?criteria=7805&doy=28m12&source=15
the 7805 Value Brand?
thanks
mrlennon
if the ic regulator is leaky them im sure it would cause it to stop in standby most of the time, ( 1 sec them back off) well i cant only try and change it least it will rule out the possibility of a faulty ic regulator,
ok the part number is HVIMC7805C, 2nd part number is: KA7805-ABTU.
will this one be ok as a replacment http://www.maplin.co.uk/Search.aspx?criteria=7805&doy=28m12&source=15
the 7805 Value Brand?
thanks
mrlennon
Hi mrlennon,
May as well change it. 7805's are cheap. If the original is insulated you may need a mica insulator and grease (plus bushing). Have a good look at all the other solder connections while you are there. Don't use too much solder if you redo the connections.
Yes, you can use those.
-Chris
May as well change it. 7805's are cheap. If the original is insulated you may need a mica insulator and grease (plus bushing). Have a good look at all the other solder connections while you are there. Don't use too much solder if you redo the connections.
Yes, you can use those.
-Chris
thanks anatech will grab one tommorow mate,
also i managed to get a reading off the ic regulator with amp in standby,
16.05v pin 1 & 2, 11.06v pin 2 & 3
this sound good or bad.
also the ic regulator i tested HVIMC7805C, theres another regulator on the video board HVIL7805CP, are bacically the same ic,s ? i know this part number differs but just curious if i could use that as a replacment if not no worries will grab one tommorow mate.
also i managed to get a reading off the ic regulator with amp in standby,
16.05v pin 1 & 2, 11.06v pin 2 & 3
this sound good or bad.
also the ic regulator i tested HVIMC7805C, theres another regulator on the video board HVIL7805CP, are bacically the same ic,s ? i know this part number differs but just curious if i could use that as a replacment if not no worries will grab one tommorow mate.
Hi mrlennon,
You should get +5V from the output to ground. That's assuming the center pin is grounded. This part has a 25 VDC maximum input voltage.
For safety, measure from ground to the end pin on your right looking at the front of the chip.
Leave the other one alone and replace that one when you have a new one.
-Chris
You should get +5V from the output to ground. That's assuming the center pin is grounded. This part has a 25 VDC maximum input voltage.
For safety, measure from ground to the end pin on your right looking at the front of the chip.
Leave the other one alone and replace that one when you have a new one.
-Chris
Hi mrlennon,
The DC measurement is fine. The regulator appears to be working okay. I would normally measure the AC ripple on each side to confirm all is well. I also look for oscillation on the output in case the caps have gone open.
I'd be more concerned with solder joints in that area. Also check the small protection transistors in the channel you had to repair. Remember they may test fine. Where was that partial schematic you posted?
-Chris
The DC measurement is fine. The regulator appears to be working okay. I would normally measure the AC ripple on each side to confirm all is well. I also look for oscillation on the output in case the caps have gone open.
I'd be more concerned with solder joints in that area. Also check the small protection transistors in the channel you had to repair. Remember they may test fine. Where was that partial schematic you posted?
-Chris
ok just a update,
i replaced the voltage regulator, as well as a 16v 470uf also a 16v 100uf and a 16v 220uf elec capacitors,
amp still goes off at set intervals, sometimes goes straigh back off other times will stay on for about 10-15 mins before it just shuts down to standby, and im not getting a protect error come on the amps screen its just shutting down ?,
i monitored the bias on the surround channel and it seemed ok,
they are set the lowest they can go about 5.5mv, i then removed Q684 and cleaned the pads and resoldered, i also replaced a 50v 10uf capacitor next to it, just to be sure as i had one spare,
amp is still acting the same? still being stubborn.
i replaced the voltage regulator, as well as a 16v 470uf also a 16v 100uf and a 16v 220uf elec capacitors,
amp still goes off at set intervals, sometimes goes straigh back off other times will stay on for about 10-15 mins before it just shuts down to standby, and im not getting a protect error come on the amps screen its just shutting down ?,
i monitored the bias on the surround channel and it seemed ok,
they are set the lowest they can go about 5.5mv, i then removed Q684 and cleaned the pads and resoldered, i also replaced a 50v 10uf capacitor next to it, just to be sure as i had one spare,
amp is still acting the same? still being stubborn.
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