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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Behringer PMP1000 amp , audio output died in use
Not got inside yet and before doing so, less I disturb something.
Inserting a mono jack in one of the input channel I/O Insert sockets, kills throughput to phones and also amp hiss at the phones output. The PMP1280 SM ,out there, does not seem to have a control line attached to the I/O insert socket switches at all , so different there , unless there is some sort of auto lack-of-signal mute circuit somewhere. At the moment I wanted to rule out something silly in the way of a wrong switch setting combination or something. The user manual shows nothing that could cause this. |
#2
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Behringer PMP1000 amp , audio output died in use
The Insert socket is a normally closed switched stereo socket between the
Mic and Line amplifier and the rest of the channel circuitry. The Tip is the Send, the Ring is the Return. So inserting a mono jack will just disconnect the mic and line amp signal from the rest of the channel, and short out the input (Return) to the rest of the channel. Effectively, all you are doing is shorting the signal going to the EQ section and beyond. There should be no interaction with any other part of the desk, and no need for any, I have never heard of any Insert being anything other than just an inline send and return. The only thing you should notice is that any noise from the Mic/Line amp in that channel will be effectively muted. Gareth. "N_Cook" wrote in message ... Not got inside yet and before doing so, less I disturb something. Inserting a mono jack in one of the input channel I/O Insert sockets, kills throughput to phones and also amp hiss at the phones output. The PMP1280 SM ,out there, does not seem to have a control line attached to the I/O insert socket switches at all , so different there , unless there is some sort of auto lack-of-signal mute circuit somewhere. At the moment I wanted to rule out something silly in the way of a wrong switch setting combination or something. The user manual shows nothing that could cause this. |
#3
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Behringer PMP1000 amp , audio output died in use
Oops, excuse the top posting, don't know how that happened!
Gareth. |
#4
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Behringer PMP1000 amp , audio output died in use
On 26/07/2015 11:06, Gareth Magennis wrote:
The Insert socket is a normally closed switched stereo socket between the Mic and Line amplifier and the rest of the channel circuitry. The Tip is the Send, the Ring is the Return. So inserting a mono jack will just disconnect the mic and line amp signal from the rest of the channel, and short out the input (Return) to the rest of the channel. Effectively, all you are doing is shorting the signal going to the EQ section and beyond. There should be no interaction with any other part of the desk, and no need for any, I have never heard of any Insert being anything other than just an inline send and return. The only thing you should notice is that any noise from the Mic/Line amp in that channel will be effectively muted. Gareth. "N_Cook" wrote in message ... Not got inside yet and before doing so, less I disturb something. Inserting a mono jack in one of the input channel I/O Insert sockets, kills throughput to phones and also amp hiss at the phones output. The PMP1280 SM ,out there, does not seem to have a control line attached to the I/O insert socket switches at all , so different there , unless there is some sort of auto lack-of-signal mute circuit somewhere. At the moment I wanted to rule out something silly in the way of a wrong switch setting combination or something. The user manual shows nothing that could cause this. So normal action. If you plug a guitar , so mono jack, in those I/O sockets then no guitar throughput, but other channels should be normal . I'll try signals in 2 channels, different socket classifications, before opening up. It all seems a bit odd having a 1/4 inch socket, per channel marked Line/Mic and not instrument, and the other one I/O , plus XLR for mic |
#5
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Behringer PMP1000 amp , audio output died in use
"N_Cook" wrote in message ... On 26/07/2015 11:06, Gareth Magennis wrote: The Insert socket is a normally closed switched stereo socket between the Mic and Line amplifier and the rest of the channel circuitry. The Tip is the Send, the Ring is the Return. So inserting a mono jack will just disconnect the mic and line amp signal from the rest of the channel, and short out the input (Return) to the rest of the channel. Effectively, all you are doing is shorting the signal going to the EQ section and beyond. There should be no interaction with any other part of the desk, and no need for any, I have never heard of any Insert being anything other than just an inline send and return. The only thing you should notice is that any noise from the Mic/Line amp in that channel will be effectively muted. Gareth. "N_Cook" wrote in message ... Not got inside yet and before doing so, less I disturb something. Inserting a mono jack in one of the input channel I/O Insert sockets, kills throughput to phones and also amp hiss at the phones output. The PMP1280 SM ,out there, does not seem to have a control line attached to the I/O insert socket switches at all , so different there , unless there is some sort of auto lack-of-signal mute circuit somewhere. At the moment I wanted to rule out something silly in the way of a wrong switch setting combination or something. The user manual shows nothing that could cause this. So normal action. If you plug a guitar , so mono jack, in those I/O sockets then no guitar throughput, but other channels should be normal . I'll try signals in 2 channels, different socket classifications, before opening up. It all seems a bit odd having a 1/4 inch socket, per channel marked Line/Mic and not instrument, and the other one I/O , plus XLR for mic Yes, a mono jack into the Insert socket will produce no sound whatsoever, it is not an input socket. However, if you plug a mono jack in part way, so the plug tip makes contact with the socket's ring connector, you CAN often inject a signal into the channel. However, this part of the circuitry is at line level, so a guitar is very unlikely to have enough output for this method to be useful. You'd stand a better chance using the proper line input socket and the gain control, or possibly the Mic amp with a suitable adaptor cable, or better still use a DI box, that's what they are for. Interestingly, the Power Amp Insert sockets are wired the other way - tip is return and ring is send - so plugging a mono jack in these WILL overide the mixers output and make sound. Gareth. |
#6
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Behringer PMP1000 amp , audio output died in use
PA and PREA work separately and as normal but low output at normal
signal input and control levels. I don't think I've come across this situation before. The ground or common to all the "level set" pots on all the channels is missing presumably. You can only get normal throughput with the pots set in range 95% to 100% of each of their tracks, jumping from very low to max in a couple of mm of movement and all such pots would not have failed at the same time. So inside we go. |
#7
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Behringer PMP1000 amp , audio output died in use
Made 2007
Although the pmp1000 uses 4580 opamps like the 1280, not the same in the prea area. The wipers of the level pots there are at ground, "low" and "high" via Rs/Cs to opamp inputs. The 1000 has stereo pots, the pairs of low-side, wipers or high-side are not connected together, but similarly close connected to opamp inputs. Without a SM this will be a pain. Next thing is check +/-rails for the opamps. |
#8
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Behringer PMP1000 amp , audio output died in use
+/-15V on the "level" opamps, and 48V and 5V for digital.
Looks as though I'll have to trace out the schematic around one of these pots and opamps to see what could be common to all the channels, requiring removing all the hardware to get to the other side of the pcb. |
#9
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Behringer PMP1000 amp , audio output died in use
I've just realised I've not seen a Level Set LED light on any channel
with any input. No such LEDs on the 2800 schematic. Try and find the common voltage to the transistors or whatever buffer to those on each channel, before removing all the hardware. |
#10
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Behringer PMP1000 amp , audio output died in use
Getting somewhere now. To save desoldering a shielding plate I'd been
probing the stereo channels. Problem is with 1 to 4 channels only, so removed shield. +/-15V ok on those opamps. LED supplies are off the -15V line, one zener per channel, giving nominal voltage of about -8.4V, varying a bit on each channel. Just pins 2 and 3 of each of the 4 off level double-opamp ICs show that same negative voltage on each channel, the B opamp of each is normal. Still a mystery what the problem in common is to cause that to each channel, but zeroing in. |
#11
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Behringer PMP1000 amp , audio output died in use
There are 2 simple -8.4V zener drop supplies per channel. One of those
-8.4V is connected to pin 2input and the other to pin 3 output of the opamp, what is that about? Still no wiser what the interchannel coupling problem is either |
#12
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Behringer PMP1000 amp , audio output died in use
PMH1000 schematic is very similar, 2 zener drop per ch, 2 SMPS ICs the
same etc I didn't bother checking the pots function as 4 pots would not fail in the same manner - wrong. Logo B in a triangle, blue body, marked 05 C5 02 on the underside. Very iffy resistance at both ends of the track. Used here as simple variable resistors,wiper tied to min gain end , max gain at zero ohms position. 5K Log track, mid track 300R, but last mm or so jumps from roughly 100R to 0R, similar the other end. Last 3/4mm or so very irregular resistance Took apart and cleared out the grease, same patchy response on reassembly. I don't think its wear as all pots the same at both ends (min gain end does not matter here in use as imperceptible). Perhaps the grease reacts with the track surface , scraping back the track surface , seems to make the situation worse. Same patchiness on the part of the track not swept by the wiper. Main problem was perhaps SMPS going into protect, or "digital amps" goung into protect ,as unusually amp was used outdoors in sunshine or failure of a PA-Prea insert switch if one channel failed |
#13
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Behringer PMP1000 amp , audio output died in use
Got those 4 replaced, but that would not make the amp cut out.
I'd decided the amp cutting out was due to the dI/dt protection part of the IXDD404 of the driver IC of the "digital" amps protecting, due to bad contacts of the crimps of the internal speaker wires. Then on rassembly noticed the undersides of the 3 main DC supply wires from ps to pa, the unobserved top sides, against flat steel of the mixer were not compressed. Laying over the thin edge of the steel plate vertically dividing ps and pa . Squashed against the steel screen plate , like a guillotine, under the mixer until the red one had its insulation so sqashed into a grove, as to touch ground . Cable now tied down to the vertical side of that divider , not the top. |
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