I'm working on my other 1002, the previous one is a 1000-2, (newer version) which is now working well.
The 1002 is the one that gets very hot. All final output semi's are NOS along with the front-end boards and VAS stage semi's. Rail voltage is +- 49.5 and about 2mV ripple.
DC offset is 0.5/2.0 mV. Power for the opamps is +- 16. Bias is set to 1.5mV.
So during some sound testing with a 25amp power supply and powering two small speakers at a moderate level it would pull too much current from the supply and make the over current lights blink.
The heat is coming from one of the channels, on the finals. I did not check or change the Zobel networks.
I can't find anything wrong.
Could it be an oscillation problem caused by the Zobel network? I think I read something about this...
Any advice is welcome.
The 1002 is the one that gets very hot. All final output semi's are NOS along with the front-end boards and VAS stage semi's. Rail voltage is +- 49.5 and about 2mV ripple.
DC offset is 0.5/2.0 mV. Power for the opamps is +- 16. Bias is set to 1.5mV.
So during some sound testing with a 25amp power supply and powering two small speakers at a moderate level it would pull too much current from the supply and make the over current lights blink.
The heat is coming from one of the channels, on the finals. I did not check or change the Zobel networks.
I can't find anything wrong.
Could it be an oscillation problem caused by the Zobel network? I think I read something about this...
Any advice is welcome.
Do you have a scope?
Does it do this driving a resistor dummy load?
Does it draw excessive current if driven to the same level with no load?
Does it do this driving a resistor dummy load?
Does it draw excessive current if driven to the same level with no load?
I have a scope and signal gen. Will check this with and without load.
Thanks Perry
You need to do whatever you were doing when it was drawing excessive current and watch for changes in the output of the channel that was heating.
Are you sure that the bias transistors are properly mated (thermally) to the heatsink?
Are you sure that the bias transistors are properly mated (thermally) to the heatsink?
The bias semis MPSA14's are NOS. I picked a matched set (hfe). They are sandwiched correctly to the heatsink.
I will try to do some testing tonight and post results.
I will try to do some testing tonight and post results.
Perry,
So I did a test and here is the results...
Start... Idle current 1.8amp Does not go up when injecting 100Hz signal up to clip, on ether channel. NO LOAD
Lt 4ohm load
100Hz/800mV input.
5.91VRMS across load and freq is 100Hz. Current draw=7.0 amps.
After 5 minutes, Finals get to 115 deg.
Same results for Rt channel.
One thing I did notice is R304 gets to 120deg with no load and no input
R305 stays at 86deg.
I did not notice any stray frequency on scope other than about 5MHz at 1 or 2 mV on both channels. I don't think this is anything.
So If it gets this hot @ 7.0 amps, it gets real hot at 20 and up. When I had it my car along time ago, I remember it was so hot, I could smell it.
The other rubicon stays cool at this current draw of 7 amps.
HHMMM interesting.
Any thoughts
So I did a test and here is the results...
Start... Idle current 1.8amp Does not go up when injecting 100Hz signal up to clip, on ether channel. NO LOAD
Lt 4ohm load
100Hz/800mV input.
5.91VRMS across load and freq is 100Hz. Current draw=7.0 amps.
After 5 minutes, Finals get to 115 deg.
Same results for Rt channel.
One thing I did notice is R304 gets to 120deg with no load and no input
R305 stays at 86deg.
I did not notice any stray frequency on scope other than about 5MHz at 1 or 2 mV on both channels. I don't think this is anything.
So If it gets this hot @ 7.0 amps, it gets real hot at 20 and up. When I had it my car along time ago, I remember it was so hot, I could smell it.
The other rubicon stays cool at this current draw of 7 amps.
HHMMM interesting.
Any thoughts
How does the DC voltage across the terminals of the bias pots compare?
With the amp starting off cold, when you begin running it as you have in the previous tests, does the power supply FET section of the amp start to heat up?
Are you sure that both amps had the same rail voltage?
With the amp starting off cold, when you begin running it as you have in the previous tests, does the power supply FET section of the amp start to heat up?
Are you sure that both amps had the same rail voltage?
Hello... I measured across R304, 0.011 vdc and across R305, 0.021. These stay at this voltage at idle and at 7amp current draw.
I did notice one thing. With 100hz input and dummy loads hooked up bringing the amp to 7 amp of current draw, I measured the rail voltage and its +-49.3 but I decided to measure ripple at this point and its 277mV on each rail. Is this normal?
I do notice the FETs on one side heat up more than the other. The side most outboard towards the edge.
The other Rubicon 1000-2 had +-48.9 ish.
Scott
I did notice one thing. With 100hz input and dummy loads hooked up bringing the amp to 7 amp of current draw, I measured the rail voltage and its +-49.3 but I decided to measure ripple at this point and its 277mV on each rail. Is this normal?
I do notice the FETs on one side heat up more than the other. The side most outboard towards the edge.
The other Rubicon 1000-2 had +-48.9 ish.
Scott
Does the same channel heat up more quickly with the dummy loads?
The voltage on the pots isn't enough to make them heat up. Measure from the center terminal to both outer terminals for each pot.
Could another component in the area be causing the heating of the pot or is the pot the hottest part in that area?
The voltage on the pots isn't enough to make them heat up. Measure from the center terminal to both outer terminals for each pot.
Could another component in the area be causing the heating of the pot or is the pot the hottest part in that area?
Yes the left channel.
I get the same 0.011 volts on center to one terminal, the other terminal is the same potential as center pin.
C131 get up to 120deg at idle. C136 stay at 86deg. C131 is next to R304.
The ripple voltage is normal? if so, I've never knew that.
I get the same 0.011 volts on center to one terminal, the other terminal is the same potential as center pin.
C131 get up to 120deg at idle. C136 stay at 86deg. C131 is next to R304.
The ripple voltage is normal? if so, I've never knew that.
Its odd that both components are the same temperature.
Can you extend the leads on the capacitor to see if it still heats up?
Can you extend the leads on the capacitor to see if it still heats up?
I could put a new one in and leave the legs' long. I'll try it. Mite take some time, have a busy day.
Thanks Perry.
Thanks Perry.
I do have NOS for all semi's, diodes and have plenty of resistors and all types and values of caps.
Update to 1002 amp. I've remembered that when I bought the broken amp and opened it up, it had a completely vaporized Transistor ( 2sc3281 ) located at Q129 and as a reminder, it left a decent burn hole on the board. Luckily it did not burn any traces. So knowing this I started to follow all the path's from this blowout. I think the cause for the excess heat and current draw was from U107 not working properly.
Since I had everything for this amp and it will be my last repair on caraudio amps, I put new semi's, electrolyte's, and new, sockets for all the DIP IC's. For the MOSFET's I used HUFA75645P3. Ordered new Ultra Low ESR Panasonic caps for the 12v side and Cornell Dubilier for the rail filters. ( I did use 63v one's ).
For Q139, 115, I used KSA940TU and for Q102, 126, I used KSC2073H2TU.
Results, Rail voltage: +-49.5, ripple less than 2mV, DC offset -1.2 and .5 mV. Bias set to 1.5mV. Idle current: 1.75amps.
Sounds outstanding, does not get hot and does not use excess current.
I think it will be good for many years now.
Thanks Perry for pointing me in the right direction.
Since I had everything for this amp and it will be my last repair on caraudio amps, I put new semi's, electrolyte's, and new, sockets for all the DIP IC's. For the MOSFET's I used HUFA75645P3. Ordered new Ultra Low ESR Panasonic caps for the 12v side and Cornell Dubilier for the rail filters. ( I did use 63v one's ).
For Q139, 115, I used KSA940TU and for Q102, 126, I used KSC2073H2TU.
Results, Rail voltage: +-49.5, ripple less than 2mV, DC offset -1.2 and .5 mV. Bias set to 1.5mV. Idle current: 1.75amps.
Sounds outstanding, does not get hot and does not use excess current.
I think it will be good for many years now.
Thanks Perry for pointing me in the right direction.
