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Rokit 6 g2 repaired ?
One of my g2 Rokit 6 speakers started to buzz loudly. Fixed the buzz but
it now has intermittent HF tone at power up.
Background:
Rokit 6 g2, playing loudly and all of a sudden started to buzz like hell..
I powered it down, popped out the amp and connected the HF and LF outputs
to a dummy load and looked for the source of the buzz. I could see that the
signal coming from the preamp board looked ok. Voltages looked OK as well.
however there was this large square wave looking signal on the HF speaker
output. Took a look at the power supply's for the TDA's.
I found that the +/- 15V supply had a few bad caps. The 47uf caps on the
zener references measured a high esr and were low capacitance as was the
main 100uf cap. on the +15V side. C104 which was supposed to be 100uf/25V
measured 9uf with an esr of 187 ohms ! The 47uf/35V cap on the zener ref for
+15 measured 30uf w/esr 40 ohms. I replaced both 100uf/25V caps in the 15V
supply and the 47uf/35V caps on the zener references.
I replaced the caps and powered the speaker back on and sure enough
it was dead quiet. No DC on outputs. Ran a signal through it, could see a
nice clean waveform on the output, both lf and hf seemed fine.
Packed it back up and played it for about an hour. Worked find, low vol and
some pretty high volume to give it a good workout.
Turned it off, came back about an hour later and when I turned it on I got
a loud HF tone, not a buzz like before. I turned it on/off a few times. Each
time the HF tone. wft ?
Back to the bench. Off comes the back, power it up, works fine ..? I figure it
could be a connection problem between the boards as some have pointed out
this is a potential source of issues. I clean and re-seat the connection. Put
the back on and try it again. Plays great, sounds great for several hours.
Come back at night, power it on. HF tone again. Back to the bench, remove
the back and the HF tone stops. I figure it has to be a connection. So I try
best I can to get it to fail by moving the connector with no luck.
Thinking cold solder I poke around on the board moving components gently
but no joy.
Question is... has someone had a similar issue and found what was causing it ?
I checked out the Mute circuit, it seems ok. It's almost like something is
oscillating .. It only seems to happen when the unit has been used for a while
and turned off for a few hours. If I play it for an hour or so and turn it off and
back on its fine. I hate the intermittent failure type problems...
it now has intermittent HF tone at power up.
Background:
Rokit 6 g2, playing loudly and all of a sudden started to buzz like hell..
I powered it down, popped out the amp and connected the HF and LF outputs
to a dummy load and looked for the source of the buzz. I could see that the
signal coming from the preamp board looked ok. Voltages looked OK as well.
however there was this large square wave looking signal on the HF speaker
output. Took a look at the power supply's for the TDA's.
I found that the +/- 15V supply had a few bad caps. The 47uf caps on the
zener references measured a high esr and were low capacitance as was the
main 100uf cap. on the +15V side. C104 which was supposed to be 100uf/25V
measured 9uf with an esr of 187 ohms ! The 47uf/35V cap on the zener ref for
+15 measured 30uf w/esr 40 ohms. I replaced both 100uf/25V caps in the 15V
supply and the 47uf/35V caps on the zener references.
I replaced the caps and powered the speaker back on and sure enough
it was dead quiet. No DC on outputs. Ran a signal through it, could see a
nice clean waveform on the output, both lf and hf seemed fine.
Packed it back up and played it for about an hour. Worked find, low vol and
some pretty high volume to give it a good workout.
Turned it off, came back about an hour later and when I turned it on I got
a loud HF tone, not a buzz like before. I turned it on/off a few times. Each
time the HF tone. wft ?
Back to the bench. Off comes the back, power it up, works fine ..? I figure it
could be a connection problem between the boards as some have pointed out
this is a potential source of issues. I clean and re-seat the connection. Put
the back on and try it again. Plays great, sounds great for several hours.
Come back at night, power it on. HF tone again. Back to the bench, remove
the back and the HF tone stops. I figure it has to be a connection. So I try
best I can to get it to fail by moving the connector with no luck.
Thinking cold solder I poke around on the board moving components gently
but no joy.
Question is... has someone had a similar issue and found what was causing it ?
I checked out the Mute circuit, it seems ok. It's almost like something is
oscillating .. It only seems to happen when the unit has been used for a while
and turned off for a few hours. If I play it for an hour or so and turn it off and
back on its fine. I hate the intermittent failure type problems...
) The speaker is dead quiet and works fine after about 10-15 power cycles and usage over the last few days. 
, another fun thing to do is put a CD in the microwave with all the lights in the room off. It looks like a little lightning storm. Probably not good for the microwave, but I haven't hurt anything yet.
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