RANE ME-30 Graphic EQ's not passing AUDIO??? Why???

NicholasD

NicholasD

New Member
So, I have these 2 nice RANE ME 30 Graphic Equalizers that we no longer used in a Theatre and neither of them are passing any Audio! Both pass audio only in Bypass mode. All LED's and buttons on the right side seem to work. One of them has an overload light permanently on. Otherwise their faults are similar...

Please see the photos... What you see is what you get...

I certainly don't see anything obvious - maybe you do? What could it be? Transformer?
*I've re-soldered any suspicious connections and tested a few CAPACITORS but not all of them... Seems like such basic circuitry but what could be failing?? Please help if anything comes to mind...
Thanks...

Granted they are pretty old (manufactured in 1992!) but I'd like to give them new life...

RANE1.JPG
RANE2.JPG

RANE3.JPG

RANE4.JPG
RANE5.JPG
 
Check the supply voltages on that 8-pin DIP opamp in back right corner. Should have +/- voltages on pins 4 and 8. What are the part numbers of the ICs in the unit?

Craig
 
Thanks very much for chiming in Craig... OK, so The ICs seem to all have the following part numbers: 4741D JRC M3041F
Does that mean anything to you?...

Here is a close-up pic:
IC.JPG


As for the voltages, I am not certain which pins were 4 and 8, so here is a pic showing the voltages I measured...

VOLTAGES.JPG


Also some close-ups of the OP-AMP from the top and the bottom (solder):

OPAMP_CLOSEUP.JPG
OPAMP_SOLDER.JPG
 
NAD80 said:
JRC 4741 D , C4570C IC's. https://pdf1.alldatasheet.com/datasheet-pdf/view/6771/NEC/UPC4570C.html C4570 IC VCC= +/- 16vdc. https://www.njr.com/semicon/PDF/NJM4741_E.pdf. See that both 12DB and 6DB LED's are lit at the same time. Bypass is engaged. Wonder if the op-amps are blown. Is the IC in the upper right corner the same as the rest 14 pin IC's? Welcome to AK.
Click to expand...

Thanks very much NAD80... Actually surprisingly, the LED's all look lit up because of the strong overhead light that I have in the workshop. :/
The LED's function as they should (as per the button situation) Only on one unit, the OL (overload) light is permanently on...
YES, the 14 pin IC right up in the top right corner is the same as the others. There is just one different one the the high frequency bands that reads "NEC JAPAN uPC4574C 9340FH003" Same on both units. See Pic Below. The only one that is different on the whole board. Might be worth ordering new OPAMPS and seeing how it goes???... It has to be something that Could go on both units and cause the OL light on one of them?!
NEC_CHIP.JPG
 
llwhtt said:
Check the supply voltages on that 8-pin DIP opamp in back right corner. Should have +/- voltages on pins 4 and 8. What are the part numbers of the ICs in the unit?

Craig
Click to expand...

Hi Craig, do my above posts shed any light on things do you think? Are those measured voltages on the OPAMP suspect? Appreciate your help, thanks :D
 
Not really, pin 1 has a dot next to it. Measure pin 4 for DC referenced to chassis/ground. Then measure pin 8 which across from pin 1. I'm just trying to see if the power supply/regulators are working.
 
Also, if you have a high voltage (near the supply voltages) at the output pin, that usually means the opamp is toasted.

Many Opamps are cheap, I'd replace them if in doubt, but without experience they are not very easy to desolder. If you plan to remove them, try to cut the leads before desoldering, and then remove the leads one by one. Priority is to save the PCB traces, not a burned IC.
 
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elnaldo said:
Also, if you have a high voltage (near the supply voltages) at the output pin, that usually means the opamp is toasted.

Many Opamps are cheap, I'd replace them if in doubt, but without experience they are not very easy to desolder. If you plan to remove them, try to cut the leads before desoldering, and then remove the leads one by one. Priority is to save the PCB traces, not a burned IC.
Click to expand...

Thanks very much for this... really appreciate any input, thoughts and tips... I have ordered some new Opamps from China and will report back when they arrive and I have put them in. As you say, they are cheap so definitely worth a shot!
 
Where are you located? Opamps are very common devices you can usually get locally.

Anyway do some voltage tests as suggested. Check + and - supply voltage, and voltage at the output pins. All refered to ground. Perhaps you don't need to replace all of them.
 
Replacing the opamps willy nilly is not the correct way of repairing something. You need to make sure the power supply is working first. If the voltages are OK then you start tracing the signal starting at the input and then see where it stops. And ordering parts from China is definitely not the right thing to do.

Craig
 
llwhtt said:
Not really, pin 1 has a dot next to it. Measure pin 4 for DC referenced to chassis/ground. Then measure pin 8 which across from pin 1. I'm just trying to see if the power supply/regulators are working.
Click to expand...

OK, so, interestingly the measurements Voltage (DC) measurement on ALL OP-AMP pins referenced to chassis ground was 0V or ngligible! (there is unfortunately no dot next to pin 1 so I just tested them all). However, on AC I got a reading of 30 to 37 Vac on all pins?!? This is when grounded to the mains earth. When grounded to the PCB to chassis screw, this was only 3Vac. Does this shed any light on the problem?
 
llwhtt said:
Replacing the opamps willy nilly is not the correct way of repairing something. You need to make sure the power supply is working first. If the voltages are OK then you start tracing the signal starting at the input and then see where it stops. And ordering parts from China is definitely not the right thing to do.

Craig
Click to expand...

Hi Craig, can sure appreciate this but perhaps I am not skilled enough to test each component from the power supply on as I simply don't know the path and voltages I should be seeing... Does this tell you anything (as per above post)? :Interestingly the measurements Voltage (DC) measurement on ALL OP-AMP pins referenced to chassis ground was 0V or negligible! (there is unfortunately no dot next to pin 1 so I just tested them all). However, on AC I got a reading of 30 to 37 Vac on all pins?!? This is when grounded to the mains earth. When grounded to the PCB to chassis screw, this was only 3 to 5Vac.

For the record the parts ordered from China are exact replacement parts so I doubt that there would be any issue here, and from where I am sitting, for a few dollars, I really have nothing to loose... These EQ's seem fairly simply built and it has to be a compponent that would fail in both of them.... maybe due to overheating or dirty power.

If you can help explain a little about what voltages I should be seeing, that would be a really great help, thanks!
 
Please assemble the unit, all grounds and screws connected, and measure the DC voltage at pins 4 and 8 of the 8 pins opamps, refered to chassis ground or to the PCB ground (if it's not connected to the chassis). If you have zero volt, the circuit is not powered and that's why it doesn't work.

Expect +15V at pin 8 and -15v at pin 4 with a split power supply. Or around 28-30v at pin 8 and zero at pin 4 with a single power supply.

The engraved dot on the plastic body indicates pin 1. Read the datasheet to see the pinout.
 
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Are you using stereo 1/4 inch headphone adapters or mono 1/4 inch headphone adapters on your input/output?
I noticed you have 1/4 inch headphone adapters in your pic,since these are single channel EQs,mono 1/4 inch headphone adapters should be used. Sorry if you already said something about this but that was one the reasons my dual mono separate EQs would not pass audio to my main in power amp section.
 
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