Solved TYT TH-9000D Gibberish Characters / Locked CPU Issue

Next episode of my TYT TH-9000D for APRS adventures (first episode here).

Somehow I managed to run into the gibberish characters issue, after swearing a few minutes I went to my friend Google only to find out that people had the same issue. Some people even posting “contact me private i have a fix” like here and in the comments of this Youtube video. Such behavior is just childish, my 6 years old does this like “I have a secret but I won’t tell you” but she is 6 years old… Just share the information, spread the knowledge, we are hams !

UPDATE : I ran into the issue a second time, same issue different cause. You can read about it here.

What follows worked for me, it might not work for you.

In the previous post I was reluctant to remove the radios main board, this time I had no other choice as the parts involved in this issue are on the other side.

Lets take a look at the following schematic excerpt.

TYT TH-9000D Schematic Excerpt

When the radio is turned off Q25 is conductive and pulling input DC to ground. Indeed, if you do the Ohm law math the radio is drawing about 260mA when turned off! When the radio is turned on Q25 is no longer conductive, allowing Q24 to get conductive and U2 and U3 voltage regulators are energized. The CPU gets its power from U3, failing to do so will result in the gibberish issue. Display back light is powered from U2.

In my case, and unlike in Glenn Davis Youtube video backlight is off, so I assumed the source of the issue is either U2 or something before it. After a few measurement the faulty component was found : Q24 which is failing to get conductive. I decided to short collector and emitter. In Glenn Davis’s case I guess the issue is U3 and would check if is providing 5 volts eventually tracing the voltage up to the CPU.

Now it was time to put the radio losely back together …

Aaaaaand ….

As a general rule of thumb, when one is facing the locked CPU issue, the best way to proceed is to trace the 5V voltage from U2 up to the CPU.

Good Luck !


  1. This is not a correct fix for this problem. Your CML chip has failed due to excessive vcc.
    Chip must be replaced and vcc lowered to 4.4v or less.
    I have repaired many with this issue.
    Dan N5mrg
    MRG Labs

    1. Hi Dan,

      Over the couple of years I got numerous messages about different solutions for this issue. Actually, the same symptom can have several different causes. In my case I knew what I did to run into the issue thus I looked in that direction.

      Which CML chip are you referring to?

  2. It seems my issue is a bit different. Vehicle battery was disconnected while doing repair on car. Reconnected battery and turn on rig. Comes on with the normal beep (but no display–no backlight and lcd barely visible). 2 seconds later rig shuts off. Each power on attemp results in the same.

    Wayne Bowyer/NEYZ
    1. Hi Wayne,

      This seems odd too. Yet if you can check all the power supply chain up to the micro processor to make sure you have all the required voltages.
      Mine has been working flawlessly since the 2 repairs I made to it. Is your radio directly connected to the carbattery i.e. not through the ignition key ?


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  5. Is there somewhere that one can get the schematic for this radio? Never had any luck with TYT for service information.
    I was using one for the transmit side of a 220MHZ repeater

    Todd Silk

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