Gallien-Krueger ML Series Service Manual Download | Manualshive

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Summary of Contents for ML Series

Page 1: ...Service Manual ML Series ...

Page 2: ...oubleshooting Instructions 8 Output Disabling 10 Preamp Description 12 Power Supply Start up 15 ML E Turn On Procedure 19 ML S Turn On Procedure 21 Schematics 27 Engineering Change Orders ECOs 38 ML S Bill of Materials 53 ML E Bill of Materials 60 ...

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Page 8: ...ply troubleshooting procedure 2 LED s work but no output from power amp Could be preamp or power amp problem First turn power switch off for 3 seconds then back on without input signal to clear shutdown feature Set all knobs to 10 and put in a signal at 5mVrms If there is still no output look at either end of the red and white wires going between the preamp and power amp with a scope probe If ther...

Page 9: ...leftmost terminals Check all TIP33s and TIP34s bad transistors will usually have a cracked or broken plastic body Replace both outputs if one measures bad Usually transistor replacement is all that is necessary to fix the amp unless some other problem caused the amp to fail These other problems are not within the scope to this document Note that the outputs can be disengaged by moving the clips ne...

Page 10: ...n unsafe operating condition and will disable the outputs indefinitely A circuit senses the temperature of the case of the output transistors Both sides of a stereo unit will be disabled if one side detects a problem The power switch must be turned off for 3 seconds before output power is again enabled Circuit Descriptions Output Disabling The outputs are disabled by Q648 and Q647 an A06 and A56 r...

Page 11: ...t made from precision resistors current sense resistors are 10 and is somewhat sensitive occasionally a 1K resistor must be paralleled with R777 Also the original boards did not have a spot for R741A which bleeds C741 Without this bleederC741 may charge up slowly through excess solder flux around the pins of Q742 Whenever output is inhibited for no apparent reason check Q742 and find out which of ...

Page 12: ...so lights the lead LED and puts a 0 63Vdc signal at the collector of Q30 Q26 This puts the FETs in the opposite state giving higher gain at the input and letting the signal go through the lead channel When the footswitch is inserted the channel select switch needs to be in the in position so that it is floating This allows the footswitch to perform in the same way as the front panel switch did Lea...

Page 13: ...If a stereo return is desired the Stereo Auxiliary In can be used to mix in a stereo signal without breaking the straight signal coming through It mixes in at U15 which is where the chorus and reverb signals also get mixed together into stereo The S preamp has a Stereo Mono switch with its return to allow for putting stereo effects directly in line Headphone Outputs The level at the output of the ...

Page 14: ... before the other The MN3101 U23 generates the sampling clock pulses at about 11kHz which is set by R354 R355 and C353 These clock pulses the drive the BBDs to sample the filtered signal The signal gets sampled and delayed at U22 the goes to U21 where it is summed with 6 more delay taps Taps 2 4 and 6 combine with one side of the stereo reverb and 1 3 and 5 combine with the other The final tap 6 U...

Page 15: ...nel and P602A towards the center of the board Floating Instruments All instruments including the oscilloscope must float with respect to the chassis Use a three pronged adapter for this purpose and also float the loads NOTE The voltages listed in this procedure are for a 117V ac line CAUTION Primary common transformer T523 7 floats at 160Vdc with respect to the chassis and must be distinguished fr...

Page 16: ...and the period will increase Always turn the unit off when adding or removing clips Adjust the reset as above as necessary The waveform should now be similar to Fig 2 The period and droop will be finalized below Leave the unit on IMPORTANT Only a polyester or polypropylene capacitor may be used for the oscillator which is used for temperature stability If it is necessary change one of the caps to ...

Page 17: ... transformer deign goal Once the period is adjusted with respect to the resonance adjust the droop to 10V above zero Securely glue the pot R508 Thermal Lift With both sides connected to 8 ohms set the input signal to be a 6dB 1kHz sine wave While observing the left output signal short JU789 from the left outside pin to the middle with a screwdriver After a short delay the output should go to zero ...

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Page 19: ...l should be about 22Vp p 4 Look at drain of Q48 square pad J113 7 3VDC 5 Adjust R63 1k trim for 4 0 4 5VDC on drain of Q59 J113 6 Adjust R86 1k trim for 5 8 6 2VDC on drain of Q69 J113 7 Increase gain to 10 and watch the signal become a square wave it should clip fairly evenly on both sides and reach 9Vp p 8 Decrease oscillator level to 66dBV 5mV 9 Change DVM to AC 20V scale 10 Adjust R70 50k trim...

Page 20: ...urn jack J3 4 Set output level to 10 R Channel 7 1Vrms stereo 4V for mono amp Scope switch should be set to load B 5 Push in stereo mono switch S2 signal goes away 6 Disengage stereo mono switch signal comes back 7 Push plug in the rest of the way Signal disappears again on stereo unit measures 4Vrms on mono unit 8 Flip scope switch to down L Output 7 4vrms 9 Engage stereo mono switch L Channel ou...

Page 21: ...k trim pot until signal hits the rails on both sides evenly Should be about 22Vp p 4 Look at drain of Q50 square pad J113 7 3Vdc 5 Adjust R67 for 4 0 4 5Vdc on drain of Q67 J113 6 Adjust R87 for 5 8 6 2Vdc on drain of Q78 J113 7 Increase gain to 10 and watch the signal become a square wave it should clip evenly and reach about 9Vp p 8 Decrease oscillator level to 66dBV 5mVrms 9 Change DVM to AC 20...

Page 22: ...crease rate to max Spike travel should speed up to about once every 7 seconds Reset rate to 0 15 Increase depth to max Spike should travel about 5 full divisions Reset depth to 0 16 Look at Bal Out R pin 2 left and compare to Fig 14 17 Engage stereo mono switch S5 Spike gets bigger Fig 15 18 Look at Bal Out L pin 3 center compare to Fig 14 19 Disengage stereo mono switch compare to Fig 15 20 Move ...

Page 23: ...eaker to L output switch down and listen for noise Sound should be smooth w no crackling 4 Change AC VM to 1V range 5 Noise should measure less than 400mVrms 500mV mono 6 Change speaker to R output up and listen Sound should be smooth 7 Also change scope switch up to measure noise in R channel as less than 400mVrms 8 Engage compressor switch noise should measure less than 600mVrms 400mVrms mono an...

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