Gs 300/430 Radio Improvement

justin.cockett · June 24, 2003

Following successful modification of my GS-300 MK-1 I was asked from several club owners for details about other Lexus models. Here's how to improve the Radio Treble response on cars fitted with the Pioneer KEX-M9006 and KEX-9106 AVC LAN Bus Radio head units (GS300 & 430 from August 2000)

The de-emphasis components (R701/C705 and R702/C706) are correct for Europe at 46.8 microseconds, which is very close to the 50 microsecond specification.

However there are two additional capacitors of value 0.1 microfarad which are causing the treble cut on this system. These capacitors are C709 and C710 on the "A" main unit topside of the Printed Circuit Board. These components form part of the tuner mute circuit, this circuit is part of the source switching between FM, AM, and Tape. I do not consider it necessary to replace these components with smaller values as the identical AM and Tape mute circuits do not have these components. The inclusion of these components is curious, I can only think (other than a design fault) that there is an attempt in the design to make the FM radio sound like the AM radio. In the USA AM radio has treble response to 10KHz, but in Europe because we pack in more stations, AM radio only has treble to 4.5KHz (FM Radio is 15KHz in both cases), this could be an attempt to balance the sound quality between AM and FM and explain the Lexus claim to tune the radio sound quality for European taste..... very strange indeed.

I have a copy of the schematic and the PCB layout with the two components to remove marked out. Any reasonable TV or Radio repair technician with experience of surface mount technology should be able to do this for you.

E-mail me if you would like copies of the diagrams.

JCC · June 24, 2003

Mine is a September 1999 model. I do not know what type of radio it is. How do I find out? Can you post the info on this topic? I could not email you. Can you email it to me?

justin.cockett · June 24, 2003

Hi, the model number is on the back of the radio unit. e-mail me on justin.cockett@btopenworld.com.

Best regards.

wilsonscullion · July 27, 2003

Hi Justin,

I'm just about to buy a 2001 GS300 with Sat/Nav. On test drives, I too noticed the terrible treble response on FM. I even took a casette recording (of an FM programme done at home) to my local Lexus dealer in Bracknell. Switching between cassette and FM showed jusy how awful the response is ( seems to be way below 10 Khz). The salesman agreed, and said he was aware of the problem. Even the Mark Levinson system in a brand new LS 430 showed that FM performance is still bad. I want to buy the car next week, and would love your assurance that the removal of the two caps. truly removes the veil over FM. I will get an approved Pioneer service centre to do it, as my hands are a bit shaky to even consider touching surface-mount components.

The Lexus salesman at Guildford( where the car is ) got hold of some info saying the Pioneer model nos. fitted to the GS are KEX-M8076ZT; KEX-M8176ZT or KEX-M8476ZT. Do you recognise these numbers( which all appear with the normal non-Sat/Nav front panels)?. They are different to your nos.( M9006 and 9106), so I'm wondering whether the component numbering would be the same.

I'd be extremely grateful if you could email me the circuit diagrams mentioned above. I've just joined the site today, so don't yet know to to send emails via the site.

Finally, last year I bought a Lexus/Toyota 4.0 GTL Soarer, which I loved, but sold recently as we're trying to move, and didn't have room for the extra car. That's what put me on to trading my ageing BMW 7-series for the GS.

Hope you can help, as I only listen to the radio in the car.

Thanks

Wilson Scullion

Richie · December 17, 2003

I have a 98 GS300 with the navi.

Has anyone modified this radio?

wilsonscullion · December 20, 2003

Hi Richie

I gave up trying to the right info from either Lexus or Pioneer. I was told I could buy a service manual from the people who repair the Lexus radios for almost £90, and it even took me weeks to get that out of Lexus UK.

So all I've done is set the frequency controls at

Treble + 7

Mid -5 or -6

Bass -2

This effectively boosts the high frequencies by a few dB, and actually makes the radio listenable to. Volume has to be inceased a bit, but there's enough there.

If you constantly switch between CD and radio, this would be a nuisance, as you'd have to reset the equaliser each time, but as I really only listen to the radio, it works fine. The sound may not suit you though, but the info's free!!

Best regards to all at Xmas

Wilson Scullion