Kenwood GE-7030 Equalizer troubleshooting - where to start - Dropping volume, All functions work

[Sam08861]

I've got a GE-7030 equalizer, that has developed an odd condition..

All functions work, sound is clear on both channels, but ~20db lower in volume than the input. I am guessing this amount, because when using the attenuate function on my pre-amp, it seems to be about the same volume, when bypassing the processor circuit. I've ruled out the preamp by using jumpers on the processor out/in. When using the eq's bypass mode, the volume doesn't increase. Turning the unit off, and it's just slightly louder, but still ~20db less loud than if the unit is bypassed. (either with patch cords or the pre-amps bypass function)

Here's the eq, doing it's thing with the top off.



So I am thinking the amp section in the EQ is not working.

A web search suggests checking capacitor c93, but I don't have a capacitor checker.

See here -----> http://fixmystereo.blogspot.com/2015/01/kenwood-ge-7030-graphic-equalizer.html

In my particular case, the sound isn't distorted, but very low, as opposed to the person above's issue.

The suspected cap from the above link.



In my spares, I do have a 160V 10uf cap that I could try as a replacement. Unfortunately, it's radial and the voltage is not the same. (spec is 35V, so this is much higher)


In my unit, all capacitors appear to be ELNAs and the originals as I can't find any evidence on the solder side of these being replaced, and have found threads with folks saying that they also had Elnas as OEM.



Couple more shots from the top, showing the boards..





I've tested the voltage at all the test points on the board that have the voltages labeled, and all checks out. Adjusting the EQ settings actually works, so it seems everything is working and I am suspecting the AMP sections.

Any advice where to start?

Shall I just try replacing c93 the the 'suntan' cap as a test, or is there a more scientific way to narrow down what the problem might be?

Will be glad to take close ups of anything if that helps.

Looking at the service manual, I can't see any specific steps or adjustments, but the schematics are provided. Unfortunately, I'm a total novice with electronics, so not sure where to start.

Found the service and owners manuals here for easy reference...

https://www.hifiengine.com/manual_library/kenwood/ge-7030.shtml

 

[Sam08861]

fyi... section of schematic from service manual above, showing amp section... Any tests I can perform here? voltage checks?

 

[Sam08861]

As an update, checked the voltages at the pins for the ICs and all check out except pins 28 on IC1 and IC2. It's labeled as NC (assuming not connected) but measures 0v instead of 1.0V. (see 3rd photo in previous post) . Could these ICs be bad? Looks like these are available online. Here's the data sheet from mouser.

https://www.mouser.com/ds/2/294/NJU7305_E-53219.pdf

Will go ahead and try swapping c93 to see if that helps.

edit... swapped out c93. Might be a little louder, but I cant tell.
One other observation, if I turn all the 'sliders' to +10db, the volume is about the same as bypassing the eq. Guess I could use this as a 'cut' equalizer but annoyed as I shouldn't have to do that.

Being an electronics novice, befuddled as to next steps. Looking at the service manual for the 7030, it mentions to reference the 7020 manual, so wondering if there's more info there. If anyone has this I'd love to take a look.

Should I just try replacing all the caps? There's only about 25 or so and easy to reach.

Any and all suggestions much appreciated.

 

[Sam08861]

As another update. Turning the mixing mic knob all the way down increases the volume a bit, so now the unit is the same volume as when bypassed with the sliders set at +8db.

 

[Sam08861]

Hi rjsalvi,

The gain levels are reduced even if the eq effect is off or the unit is shut off. The same ~8db less. It's as if something in the signal path is parasitic to the volume. Perhaps the circuit path itself? Haven't tried with the eq unplugged, but will try that now.

edit... with the unit unplugged, there is no sound, unless the preamp is turned all the way up, there there is a very faint scratchy sound.

Also, the voltage at the op amp pins (8 pins, labeled as ic7 on the schematic) checks out. However, not sure if this tells me if the op amp is good or not.

I do have an oscilloscope, if there is some way of using this to trace down the issue.

 

[Sam08861]

Looking at the schematic, it appears the signal path is as follows (LEFT CHANNEL):

Input

C3
PIN 15 IC3
PIN 17 IC3
C99
R37
C5
PIN 15 IC5
PIN 17 IC5
C13
R43

OUT

Could I trace the signal with the oscilloscope to see where it reduces in amplitude to see what components might be the problem? Limited experience with this device, so would need help with settings, etc.

Checking the remaining voltages in the diagram, every last one checks out. One thing, to on the display board side, all are about .1 or so V off from spec. (some slightly higher, some slightly higher. For instance getting 5.045 instead of 5.1,etc.). The only ones not corresponding to the schematic are pins 28 on IC1 and IC2, both giving zero instead of the indicated 1 V.

On the amp / power supply side, everything is within a few hundredths, with the exception of pin 28.

 

[sregor]

Maybe muting? Q1, Q2 and Q3 are part of a turn on muting circuit. Simple test is to disconnect Q1 and Q2 emitters (leads that go to output line - not clear in the posted schematic. when circuit is turned on, voltage across Q3 b-e causes it to conduct and mute the output, until it diminishes to less than .6 across Q6, then all should be not conducting during normal operation. Good Luck

 

[Sam08861]

Thanks rjsalvi,

I was wondering if indeed this is how the EQ is supposed to work. The spec's state a '0db gain' with +12db / -12db range, but in reality, the possible adjustments are +4db / -20db. However, when I first hooked it up a few weeks ago, the volume was the same as when bypassed. It could possibly be that the prior/default settings from the PO were set all the way up. Also, I did a lot of a/b comparisons by using the preamps 'rec out' button for switching back and forth with my saved eq curves, so I do think it's definitely different than before. You're right in that it affects both channels is odd and therefore not likely to be in the discrete left/right circuits. I do tend to play music and walk away, so it's possible one channel followed the other and I just didn't notice.

Perhaps someone with the same unit can verify how theirs works.

The unit is equal to being bypassed with the 'sliders' at +8db, and a bit louder than with no eq with them set all the way up at +12db.

By the way, did purchase the 7020 manual, and it has circuit diagrams and a number of pinouts, block diagrams, etc. Will be glad to take screenshots of anything in there that might be helpful.

Thanks Steve,

Was just reading up on how to trace the signal path and ran across a practical summary on testing transistors here https://www.diystompboxes.com/pedals/debug.html so was wondering if perhaps there was some testing to be done here, although would not have thought about the muting circuit.

Here's a close up from the 7020 manual of the muting section with q1, q2, q3 and what I'm assuming are labels for the (B) base and (E) emitter pins.
From the diagram below, I'm thinking that Q1 is left out and Q2 is right, so perhaps I can test one at a time and be able to compare left/right volume?

 

[Bob]

I second @sregor's recommendatation. muting circuits I have futzed with
all drop the volume but not to nothing. you can still hear sound but at
a very low volume.

 

[Sam08861]

Thanks Bob,

Will give that a go and report back.

 

[Bob]

use a jumper with mini-plug grabbers and locate where the signal goes into the muting
circuit and then where it comes out (or where the signal output "terminal" is)
and bypass.

I hate muting circuits, the dh110 hafler preamp, has this problem when one/two channels
distort and/or are dead.

 

[sregor]

use a jumper with mini-plug grabbers and locate where the signal goes into the muting
circuit and then where it comes out (or where the signal output "terminal" is)
and bypass.

I hate muting circuits, the dh110 hafler preamp, has this problem when one/two channels
distort and/or are dead.

Can't really bypass without cutting a trace. Simplest to disconnect (unsolder) emitters of Q1 and Q2 (or unsolder them completely)

 

[Sam08861]

Thanks both! I was studying the diagram and trying to figure out where I could jump and I like the idea of removing the transistor, rather than bending up a leg, as I tend to break things with my lack of delicate motor skills. (10 thumbs!)

 

[Sam08861]

Tried removing Q1 and Q2 and no change. Resoldered all the original caps/transistors back in and zipped her back up. Works good enough and very quiet, so will leave it alone for the time being.

Perhaps someone with an EQ can comment if theirs is equivalent volume as compared to when bypassed/out of the loop.

 

[FastEarle]

Tried removing Q1 and Q2 and no change. Resoldered all the original caps/transistors back in and zipped her back up. Works good enough and very quiet, so will leave it alone for the time being.

Perhaps someone with an EQ can comment if theirs is equivalent volume as compared to when bypassed/out of the loop.

I recently got one of these and there does seem to be a mute of some kind. I have to turn my Yamaha up quite loud to get the display to show signal. I have this in between my Yamaha rxv1500 and some klipsch the sixes, powered speakers. I can get good volume, but have to turn up the receiver more than I think I should. The sound is fantastic though...
Earle

 

[Sam08861]

Thanks for the reply! Glad to know it wasn’t a defect. I don’t have this in my system anymore since moving to active crossover, but just today, was thinking about putting it into an output from my preamp just for the light show!

 

[FastEarle]

Thanks for the reply! Glad to know it wasn’t a defect. I don’t have this in my system anymore since moving to active crossover, but just today, was thinking about putting it into an output from my preamp just for the light show!

I do wish there was a way to adjust the display sensitivity however. Especially for lower volume listening.... That's the only complaint I have about this unit... Earle

 

[Sam08861]

I do recall somehow getting the display to show a full range. I'll have to hook mine up again and see if I can duplicate what I did previously.

Will try and do this during the week and report back on whether or not I have any luck.