i have the Mark Levinson No.27, for some reason it keeps going into protection mode . As soon as it turns on, after few seconds, it turns itself off.
When I removed the right channel, it works perfectly, but when I removed the left channel ,switched on the right channel, , it was shutting down quickly when the power. I think the right channel is bad.
anyone know how to repair it? thanks!
When I removed the right channel, it works perfectly, but when I removed the left channel ,switched on the right channel, , it was shutting down quickly when the power. I think the right channel is bad.
anyone know how to repair it? thanks!
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Hi,
does anyone have biasing information and voltages for the 27.5? The sm doesn't seem to have those. There seem to be 2+2 pots on AC-8 + 8.5 per channel.
Thanks!
PS: mine is outputting audible noise (around 25mVpp) on both channels when idle (shortened inputs). Will start looking into this.
does anyone have biasing information and voltages for the 27.5? The sm doesn't seem to have those. There seem to be 2+2 pots on AC-8 + 8.5 per channel.
Thanks!
PS: mine is outputting audible noise (around 25mVpp) on both channels when idle (shortened inputs). Will start looking into this.
After correcting bias, checked Vreg and Vunreg, which show significant ripple. VREG should have less than 3mVpp afaik, one side has 50 in my case. For Vunreg mine (27.5) has 300mV ripple.
I understand the 45000uF 75V 95°C and 1900uF 150V 85°C are custom made and not available on the market. Has anybody figured out alternatives yet?
Thanks
I understand the 45000uF 75V 95°C and 1900uF 150V 85°C are custom made and not available on the market. Has anybody figured out alternatives yet?
Thanks
Did you eventually solve your problem ?
It sounds as if one of the heat sensors on the heatsinks or the cabling to connect them is giving trouble.
Second reason can be DC on the LS output.
Hans
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Thanks for helping, Hans.
I had measured the bias from another 27.5 recently serviced by a ML dealer, it was set to 104mA, which is in line with your value (I measured voltage over R125+R127 only).
Vreg was set to +-64,50V (end value after full warm-up) rather than the specified 65V. I left it at 64,5V, probably goes up 100mV with higher ambient temperature in summer.
BR
I had measured the bias from another 27.5 recently serviced by a ML dealer, it was set to 104mA, which is in line with your value (I measured voltage over R125+R127 only).
Vreg was set to +-64,50V (end value after full warm-up) rather than the specified 65V. I left it at 64,5V, probably goes up 100mV with higher ambient temperature in summer.
BR
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While waiting for parts, I further investigated the idle noise issue, mentioned before. It's on both channels, stronger in the right channel (only hear it if I sit 1m from the tweeter).
I shorted driveline + (Pos_Drive: P6, Neg_ P7) to ground via capacitator. The noise is gone. So either it really is dirty VReg, or something else is uncough on AC-8.5 board. We will see.
Seems I'll have to take apart AC-8.5 and AC-8. They are connected to each other with these 'concorde pins'. I had hoped this is some kind of connector, but it seems soldered on either side of the board. That's a bit inconvenient.
BR
I shorted driveline + (Pos_Drive: P6, Neg_ P7) to ground via capacitator. The noise is gone. So either it really is dirty VReg, or something else is uncough on AC-8.5 board. We will see.
Seems I'll have to take apart AC-8.5 and AC-8. They are connected to each other with these 'concorde pins'. I had hoped this is some kind of connector, but it seems soldered on either side of the board. That's a bit inconvenient.
BR
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Before you take things apart, which is indeed very inconvenient, I strongly advise to first replace the two 680uF caps on the upper board and to make Vreg+ equal to Vreg-.
When these two voltages are not equal in magnitude, the start up circuit interferes with the signal chain, that's why.
Hans
When these two voltages are not equal in magnitude, the start up circuit interferes with the signal chain, that's why.
Hans
Hello, Hans! Did I understand correctly that the amplifier will not start if the currents from both channels are not the same? I have this problem: I replaced the entire small electrolyte with 4 * Sprague 68uf 25V; 4 * ekz ROE 22uf 63v, 10uf 4 NIC, 6* Bourns trim resistors with resistance setting over the old resistors,all yellow yellow film capacitors 0.1 uf 160v.
I did say that the regulated voltages have to be of exact the same magnitude for each channel, not at all the currents of both channels.
What do you mean with “there is no start mode ....” ?
What model do you have to 27 or 27.5 ?
Hans