Hello
I have an intermittant problem with my quad 34 preamp. Sometimes when I switch it on most of the lights light up partialy. The radio light is normal brightness and radio is selected. There is very slight distortion when this happens, mostly I switch on and its normal, say ninety percent of the time its normal.
It is one of the first 34s and I do have a schematic issue 1 M12746 up to sn 6000
It still works, press aux and that light brightens and aux is selected. The filters also light up partialy but are not operating.ny ideas anyone.
Thanks
thyristor44
I have an intermittant problem with my quad 34 preamp. Sometimes when I switch it on most of the lights light up partialy. The radio light is normal brightness and radio is selected. There is very slight distortion when this happens, mostly I switch on and its normal, say ninety percent of the time its normal.
It is one of the first 34s and I do have a schematic issue 1 M12746 up to sn 6000
It still works, press aux and that light brightens and aux is selected. The filters also light up partialy but are not operating.ny ideas anyone.
Thanks
thyristor44
It seems like the power to the switching logic circuits could be a bit weak. These LEDs and their associated signal routing switches are all operated and latched the old way, with a few CMOS ICs like 4001, 4013 gate arrays to do the logic and indicator LEDs plus several 4016 bilateral switch arrays to do the actual signal selection and routing function.
Check that the logic circuit power supplies are +/- 7.5V and also at the IC pins 4 & 7. (+8.6/-9.4V is for the audio dual opamps) are correct and don't sag to useless levels under the load of the LEDs being switched. There could be several faults that cause problems there, including contamination or dirty button switch contacts, caps in the power supply and local decoupling, dry joints on the PCB, poor or loose coupling contacts to the switch pad, interconnecting cables even crook ICs, but checking the power and its steadiness to the logic ICs will be a start to narrowing down which.
If you haven't already read this, you or others may find a little encouragement here: QUAD 34 pre amplifier Modification and information
Check that the logic circuit power supplies are +/- 7.5V and also at the IC pins 4 & 7. (+8.6/-9.4V is for the audio dual opamps) are correct and don't sag to useless levels under the load of the LEDs being switched. There could be several faults that cause problems there, including contamination or dirty button switch contacts, caps in the power supply and local decoupling, dry joints on the PCB, poor or loose coupling contacts to the switch pad, interconnecting cables even crook ICs, but checking the power and its steadiness to the logic ICs will be a start to narrowing down which.
If you haven't already read this, you or others may find a little encouragement here: QUAD 34 pre amplifier Modification and information
Thanks Ian
I will check these voltages and joints at the weekend. I may be able to borrow a spare 34 so that will take some pressure off as I use it every evening.
I will check these voltages and joints at the weekend. I may be able to borrow a spare 34 so that will take some pressure off as I use it every evening.
Check for damage caused by leaking electrolytic capacitors, wost of the switching lines are carried in the top side of the board and are often etched away by the leaking electrolyte
Stuart
Stuart
Sorry 405man for the rudely late reply. I didnt check for more posts.
I still have the same fault but am reluctant to take the 34 out of service and open it up till I get something else to use.
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