I have in the workshop a Mark Levinson 38 preamp with odd fault. There is NO volume control even though the 'numbers in the display' change with rotation of the volume control or with the remote control. The output remains at a fixed level (high).
It does work when 1st turned on so I guess it is out with the freezer spray on the processor/surrounding caps etc.
Anyone experienced this problem?
It does work when 1st turned on so I guess it is out with the freezer spray on the processor/surrounding caps etc.
Anyone experienced this problem?
How the volume control works:
After passing through a couple of opamps the signal is applied to the Vref inputs of a current output 12-bit 8222 DAC. If you're constantly getting full output this probably means that all data inputs to the dac are constantly high or the dac is blown - easy to check. If true check the shift registers feeding the dac and whether they are getting volume data/strobe from the micro.
After passing through a couple of opamps the signal is applied to the Vref inputs of a current output 12-bit 8222 DAC. If you're constantly getting full output this probably means that all data inputs to the dac are constantly high or the dac is blown - easy to check. If true check the shift registers feeding the dac and whether they are getting volume data/strobe from the micro.
Hi
I sort of worked out how the volume control worked in the short time after posting the enquiry. What is strange is that problem is intermittent. I'll delve deeper this evening and keep you updated. Thanks for info. 🙂
I sort of worked out how the volume control worked in the short time after posting the enquiry. What is strange is that problem is intermittent. I'll delve deeper this evening and keep you updated. Thanks for info. 🙂
As suspected the DAC inputs are all constantly high so I'm back to the shift registers. I reckon the DAC is culprit but will know when the inputs are disconnected.
Anyone with schematic?
Ta
Anyone with schematic?
Ta
Hi
Dry joints on a Mark Levinson? I don't think so. Anyway the repair is progressing. The unit works when 1st turned on but then the volume control fails to operate on one channel after short time. All the inputs to the DAC on that channel remain high (no strobe).
The inputs to the 4049's are strobing when the control is turned. I have replaced the DAC8222 but no better. I am investigating the 4049's a bit deeper. Thanks for the suggestion.
Dry joints on a Mark Levinson? I don't think so. Anyway the repair is progressing. The unit works when 1st turned on but then the volume control fails to operate on one channel after short time. All the inputs to the DAC on that channel remain high (no strobe).
The inputs to the 4049's are strobing when the control is turned. I have replaced the DAC8222 but no better. I am investigating the 4049's a bit deeper. Thanks for the suggestion.
Problem with a 380 now. All inputs fine except 4 designated SSP for a surround processor input. When this is selected it gives full volume and the volume and balance do not work.
Help!
Help!
I am resurrecting this old thread as I have a 380S I am trying to repair. Anyone with a 38 series schematic?
The problem I am having is that the unit does not boot properly. As soon as its plugged in you can hear relays clicking continuously for the period it would normally boot and then go silent. The display and leds light up but do not flash any data.
The problem I am having is that the unit does not boot properly. As soon as its plugged in you can hear relays clicking continuously for the period it would normally boot and then go silent. The display and leds light up but do not flash any data.
Hi. No schematic but your problem is most likely to be
defective capacitors in the power supply/regulation stages.
I had to 'reverse engineer' the circuit to fix the one I had for repair!
defective capacitors in the power supply/regulation stages.
I had to 'reverse engineer' the circuit to fix the one I had for repair!
I completely recapped the unit and it's behaving as I would expect a 380s would with no firmware installed - i.e. all display cells are illuminated and the preamp is non responsive. The 18CV8 PEEL device that has the programming on it has a little burn mark on the center of the sticker (was there before) so it needs replacing. Any ideas where I can get a programmed chip?
Dear,
Alas, my answer comes much too late !!
I think you have to change the ic U2101 : an ILQ2 ( a quad channel optocoupler )
Raymond