Tweet
Shure 700 Pro Master Mixer - Powered - Need Advise
Shure 700 powered mixer. he "Shutdown" LED is lit up. When I first powered this monster up, the audio had a crackle to it. More so on channel B than A. If I give it much volume at all, the audio amps shut off. I have to turn it off, wait a few minutes, and turn it on again. So, I removed the power supply boatd and found a cracked solder joint on a capacitor (the solder was completely gone), after that I have no audio, just a hum. Oh, and that cap was 1500uf, and was marked 1000uf. I plan on ordering all new caps for power and output boards. But I was wondering if anyone here has experience with this mixer and/or wouldlike to offer advise? I want to take some voltage readings, but where should I start? Thanks
pdf is in the zip file
Here are some notes taken from the service manual
Shure Pro Master 700 mixer notes
__________________________________
1.Capacitors C609 and C610 insure stability during limiting.
2.Thermistors RT602 and RT603 (mounted on transistor
Q614 and Q615 heat sinks) monitor the transistor case temperatures.
3. Diodes D609 and D608 are normally reverse-biased and
do not conduct. But with highly reactive amplifier loads, the
diodes will conduct to prevent reverse-voltage breakdown
of the output transistors.
4. Thermistor RT601 is mounted on output transistor Q613.
Comparators U503A and U503B compare a constant refer-nce voltage of 0.73V to the voltage across RT601. When
an unusually high temperature of 70°C (158OF) is reached
on the heat sink, RT6Ol's voltage will have dropped to the
reference voltage and U503A or U503B will change state,
turning on theTEMP WARNING LED (D801). If the temperature
continues to rise to 100°C (212OF), RT6Ol's voltage
drops below 0.3V, U503C or U503D changes state, turning
off Q502 and Q501, opening relay K1, and turning on the
SHUTDOWN LED (D802). In this condition, the power amps
are partially powered but all other (low-level) circuits and
the fan (BI) remain fully on. This condition remains until
the temperature on the heat sink drops to 70°C, when the
LEDs turn off and full power is restored to the power amps.
RT501 is a positive-temperature-coeffic~ent thermistor
with a threshold at 120°C (248OF). It is mounted on the
Power Supply board (A5) in front of fan 61 in the path of the
air flow through the PC board-fan assembly. When air
motion is severely restricted, RT501 heats and its resistance
Increases (from 450 to approximately 1200 ohms).
The current through R502 is reduced and the voltage
drop across R502 is not enough to keep transistor Q501
turned on. (2501 turns off, opening relay K1 and turning
on the SHUTDOWN LED. It is extremely important that
RT501 should be mounted in the path of the air flow, its
body perpendicular to the flow, approximately %" from
and not bent flat against the power supply board.,
5. The SPEAKER OUTPUTS dc sensor circuit is comprised
of comparator U504 and associated components. A portion
of the output voltage is derived from the divider network of
R640 and R641 on the power amp board. It is fed to the
comparator inputs, and capacitors C509 and C510 remove
the audio signal leaving only the dc component. When the
dc output at the SPEAKER OUTPUTS jacks exceeds + 3QV,
U504 changes state, cutting off transistors Q501 and (2502,
opening relay K1, and turning on SHUTDOWN LED D802.
Note that, when the comparator outputs change state,
diode D509 and resistor R518 cause "latching"; the power
switch must be turned off and back on to reactivate the
console. This feature is designed to call attention to the
presence of excessive dc at the output, which is an abnormal
condition and probably requires servicing.
Shure 700 powered mixer. he "Shutdown" LED is lit up. When I first powered this monster up, the audio had a crackle to it. More so on channel B than A. If I give it much volume at all, the audio amps shut off. I have to turn it off, wait a few minutes, and turn it on again. So, I removed the power supply boatd and found a cracked solder joint on a capacitor (the solder was completely gone), after that I have no audio, just a hum. Oh, and that cap was 1500uf, and was marked 1000uf. I plan on ordering all new caps for power and output boards. But I was wondering if anyone here has experience with this mixer and/or wouldlike to offer advise? I want to take some voltage readings, but where should I start? Thanks
pdf is in the zip file
Here are some notes taken from the service manual
Shure Pro Master 700 mixer notes
__________________________________
1.Capacitors C609 and C610 insure stability during limiting.
2.Thermistors RT602 and RT603 (mounted on transistor
Q614 and Q615 heat sinks) monitor the transistor case temperatures.
3. Diodes D609 and D608 are normally reverse-biased and
do not conduct. But with highly reactive amplifier loads, the
diodes will conduct to prevent reverse-voltage breakdown
of the output transistors.
4. Thermistor RT601 is mounted on output transistor Q613.
Comparators U503A and U503B compare a constant refer-nce voltage of 0.73V to the voltage across RT601. When
an unusually high temperature of 70°C (158OF) is reached
on the heat sink, RT6Ol's voltage will have dropped to the
reference voltage and U503A or U503B will change state,
turning on theTEMP WARNING LED (D801). If the temperature
continues to rise to 100°C (212OF), RT6Ol's voltage
drops below 0.3V, U503C or U503D changes state, turning
off Q502 and Q501, opening relay K1, and turning on the
SHUTDOWN LED (D802). In this condition, the power amps
are partially powered but all other (low-level) circuits and
the fan (BI) remain fully on. This condition remains until
the temperature on the heat sink drops to 70°C, when the
LEDs turn off and full power is restored to the power amps.
RT501 is a positive-temperature-coeffic~ent thermistor
with a threshold at 120°C (248OF). It is mounted on the
Power Supply board (A5) in front of fan 61 in the path of the
air flow through the PC board-fan assembly. When air
motion is severely restricted, RT501 heats and its resistance
Increases (from 450 to approximately 1200 ohms).
The current through R502 is reduced and the voltage
drop across R502 is not enough to keep transistor Q501
turned on. (2501 turns off, opening relay K1 and turning
on the SHUTDOWN LED. It is extremely important that
RT501 should be mounted in the path of the air flow, its
body perpendicular to the flow, approximately %" from
and not bent flat against the power supply board.,
5. The SPEAKER OUTPUTS dc sensor circuit is comprised
of comparator U504 and associated components. A portion
of the output voltage is derived from the divider network of
R640 and R641 on the power amp board. It is fed to the
comparator inputs, and capacitors C509 and C510 remove
the audio signal leaving only the dc component. When the
dc output at the SPEAKER OUTPUTS jacks exceeds + 3QV,
U504 changes state, cutting off transistors Q501 and (2502,
opening relay K1, and turning on SHUTDOWN LED D802.
Note that, when the comparator outputs change state,
diode D509 and resistor R518 cause "latching"; the power
switch must be turned off and back on to reactivate the
console. This feature is designed to call attention to the
presence of excessive dc at the output, which is an abnormal
condition and probably requires servicing.
Attached Files
Comment