Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
sureshm wrote:hkminn, to help me understand if we both are having the same problem, could you please connect both IN+ and IN- to GND (as Russ suggested) and measure voltage from OUT+ to GND and OUT- to GND when the power is on? Do you mean + and - for the peaker terminal by OUT+, OUT- to GND?
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:sureshm wrote:hkminn, to help me understand if we both are having the same problem, could you please connect both IN+ and IN- to GND (as Russ suggested) and measure voltage from OUT+ to GND and OUT- to GND when the power is on? Actually the only measurement that matters there is the voltage between the two OUT+ and OUT- I have measured the voltage at the output terminal with both + and - input terminals grounded : 30mv AC and 220mv DC. LM4780 still gets very hot quickly.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Do either of the outputs have DC component to GND?
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Hi Russ,
What is the nomal temperature of LM4780 on Sympatico when it is idling?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Well if it's on the heatsink it should be just warm.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:Do either of the outputs have DC component to GND? I measured across + and - output terminals and the number fluctuates between 100mv-250mv DC when the power is on. Since I am using a cheap digital multi-meter I am not sure of the accuracy, but there is DC component across OUT+ and OUT-.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Is there any DC from each output to GND?
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:Well if it's on the heatsink it should be just warm. Then, mine gets really hot for sure. It becomes uncomfortably hot to touch within a minute after I turn it on. Is it possibly oscillating?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Please measure each output compared to GND.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:Is there any DC from each output to GND? You mean across either output terminal and input signal gnd? Yes, it is around 17v DC.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
There are two vias at the output of the opa1632 can you please measure between each of those and GND?(IG is fine)
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:There are two vias at the output of the opa1632 can you please measure between each of those and GND?(IG is fine) 1632 has 8 legs. could you please specify which one?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
There are two plated vias toward the heatsink at the end of the OPA1632.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:There are two plated vias toward the heatsink at the end of the OPA1632. I got it. One on the left shows 117mv, and one on the right shows -46mv. I am measuring with heatsink farther away from me.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
I am starting to suspect a short or open (dry joint maybe) somewhere or possibly a dead LM4780 or less likely one of the opamps in the front end. Measure across each resistor and cap with a DMM and make sure none of them seem amiss. Refer to the schematic for help. It is possible to put too much pressure on the LM4780 and damage it internally. I have done this accidentally a few times. I honestly don't know what is wrong at this point. I am just giving you some ideas where to look while I continue to see if I can find anything myself. Edited by user Thursday, July 8, 2010 3:55:52 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:I am starting to suspect a short or open (dry joint maybe) somewhere or possibly a dead LM4780 or less likely one of the opamps in the front end.
Measure across each resistor and cap with a DMM and make sure none of them seem amiss. Refer to the schematic for help.
It is possible to put too much pressure on the LM4780 and damage it internally. I have done this accidentally a few times.
I honestly don't know what is wrong at this point. I am just giving you some ideas where to look while I continue to see if I can find anything myself. What about the voltages I measured. Are they all normal?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
No there should almost no voltage from each output to GND with the inputs connected to GND.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Russ White wrote:I am starting to suspect a short or open (dry joint maybe) somewhere or possibly a dead LM4780 or less likely one of the opamps in the front end.
Measure across each resistor and cap with a DMM and make sure none of them seem amiss. Refer to the schematic for help.
It is possible to put too much pressure on the LM4780 and damage it internally. I have done this accidentally a few times.
I honestly don't know what is wrong at this point. I am just giving you some ideas where to look while I continue to see if I can find anything myself. I have checked and re-heated the solder joints. I was not brave enough to touch the pre-installed SMD joints though. Since both channels have the same problem, can I rule out the possibility of bad joints or short? Also, I put a thin(2mm) aluminum tension bar behind LM4780 to fix it to the heatsink. I don't think it is possible to put too much pressure on the chip without bending the bar.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/9/2009(UTC)
Posts: 65
Location: seoul, korea
|
Hi Russ,
I have re-soldered joints and checked the circuit as much as I could.
I followed the traces in the schematics and measured resistors as you suggested (I could not measure the SMD caps though). There are some discrepancies between the actual values and the schematics, but close enough I think.
I have not found any problem in connectivity between IC's so far but there still is 17VDC on OUT terminals in both channels and the heatsink gets very hot.
Any futher suggestions?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
You just need to measure for a short across the caps. Just measure them like you would a resistor.
Other than that I can't think of anything else to check right now.
|
|
|
|
|
|
Forum Jump
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.
