Maker Pro
Maker Pro

Logitech Z553 Controller Bypass Help


Jun 29, 2020
Jun 29, 2020
tl;dr: What is (or how can I determine) the correct pinout for the Logitech Z553 controller and how can I properly bypass the controller?

I’m new to the forum and have limited experience with audio and electronics (mostly limited to a few electrical engineering courses in the distant past and wiring up audio systems in several vehicles), but I’d like to think I’m a quick learner. Thanks in advance for any help. Questions are summarized at the bottom.

I have a broken controller on my Logitech Z553 2.1 computer audio system. I know that the controller is bad since I have another identical system and swapping the controllers fixes the problem. Similarly, speakers and woofer/amp are known good. I’ve torn down the bad controller and done a lot of poking around to see if I can bypass the controller to get the system running at a fixed volume and bass level, but have been unsuccessful so far, hopefully just due to lack of experience. The cable shows good continuity on all used pins, so I’ve cut it in half and am reusing it to build the bypass.

The controller has four functions:
Volume (main knob)
Bass level (rear wheel)
Aux In (alternative aux input from aux on amp)
Headphone Out (interrupts audio to amp)

It uses a standard 9-pin D-sub, but I’ve been unable to find the pinout and can confirm through testing and observation that it does not match any of the other 9-pin Logitech controller pinouts I’ve been able to find online.

My layout is as follows:
X – BLK – GND (this is the metal wall around the pins which is grounded and attached to the copper mesh and aluminum shielding surrounding the cable)
1 – BRN – ?
2 – ORG – +0.5V (could be Standby? Connect to 5?)
3 – GRN – ?
4 – BLU – ?
5 – WHT – +18V (assumed power to connect to Standby)
6 – RED – ?
7 – YEL – ? Some sort of audio input, aux in?
8 – UNUSED (no associated conductor, verified on working unit)
9 – GRY – ? (connects to GND when unit is plugged in)

Please correct me if I’m wrong, but I’ve gleaned from other folks trying similar things that I need to directly connect my speakers to these pins (rather than to their original output ports on the amp). Would I also need to do this for the Aux In from the PC or can I still use the one on the amp?

In order to determine which pins are which, I’m assuming I’m looking for the following functions:
Power (pin 5, WHT)
GND (pin X, BLK)
Standby (assumed pin 2, ORG)
volume potentiometer
bass potentiometer
CH1 in
CH2 in
CH1 out
CH2 out

This assumes I can have all input and output channels share the ground as their negative. (safe assumption?)

So far I’ve tried several things, but the only thing that produced any sort of results was as follows: Jumping pin 5 to 2 (no resistor added), then connecting audio signal to 7 (neg to X which is GND) gets the woofer thumping at what seems to be max bass. Putting a 10kΩ resistor in series between them quiets it down to a better level (duh).

I can’t for the life of me get proper audio out of the speakers. I had assumed that with no resistance on the volume potentiometer that I’d get max volume with a direct connection. Is this a bad assumption? I get extremely quiet (but good quality) audio out of the speakers when I connect one to the same pin as the woofer (pos to 7, neg to X). I haven’t been able to hear any audio when leaving the speaker negative on X and swapping the positive to any of the remaining unknown pins (though it may have been super quiet and I just couldn’t hear it over the woofer). Is this happening because I’m connected to the headphone output channel that bypasses the amp for the L/R channels? Is there a connection on this pinout for my L/R channels?

I’ve tried tracing the PCB but it’s not something I have experience with and too many of the components are blocking visibility to the traces (and I don’t have a desoldering tools to remove parts). I can say that when attached to the board (and not the amp), pins X, 9, and 7 are all grounded, but that’s about it (and I don’t know what that’s telling me).

a) Is what I’m trying even feasible?

b) Is it safe to assume that all four channels (CH1 in, CH2 in, CH1 out, CH2 out) are sharing pin X (GND) as their negative conductor?

c) Should I be bypassing the amp’s speaker outputs in favor of a direct connection to the pinout (would the speakers still be amplified in this case) or am I stupidly connecting to the headphone output of the controller which is obviously not amplified?

d) Does this also hold true for the amp’s audio input (Aux In)?

e) Is it safe to assume that the system should be outputting at max volume through the speakers with a direct connection to this pinout (no resistance where the volume potentiometer would usually be)?

f) Are my assumed pin functions (above) correct?

g) Given that I’m getting full bass and a tiny bit of standard audio when I input signal on pin 7, does that make it CH1 or 2 in? If so, why is my volume so uselessly low for the speakers but maxed out on the woofer? Am I connecting them in a wrong location such that they are not being amplified properly? Perhaps I’m connecting them to the Headphone Out channels that aren’t going through the amp?

h) How do I nail down what my other pins are?

i) Assuming I can get everything else kicking (obviously getting ahead of myself), where should I be adding resistance to limit the bass?

Sorry for the novel and thanks again. Any thoughts are appreciated, even only for my own education.

2020-06-29 12.32.45-min.jpg 2020-06-29 12.33.08-min.jpg 2020-06-29 12.33.46-min.jpg 2020-06-29 12.34.01-min.jpg 2020-06-29 12.34.18-min.jpg