FM transmitter repair

[amdx]

I have a CZH-05B FM transmitter. It recently went low power. It will
transmit but not more than 20ft. I looked in and found an over heated
resistor, maybe two, they are close together, a shorted transistor and a
9 volt regulator putting out 10.8V.
I made an assumption that the output transistor was OK since it did
transmit, and these parts were in the predrive circuitry.
I ordered the parts, installed them and not much change in the signal,
I think there is a little more output but it's still not right.
So I opened and checked the 9v regulator output. Hmm, it 11.x volts
output.
The part I removed is labeled 78L09, it is an sot89 part. The part I
order is the same. The part I got is labeled 8H612. I'm not sure it is
the right part. I have searched for an 8H612 and find nothing. The part
I ordered is supposed to be a ST Micro part. I don't know how they mark
their parts, But I expect it would say 78L09. I will try to call
tomorrow and verify. uh, Monday.

The second problem, I should have checked the output transistor,
it is shorted. The part on the transistor is K2 092, Marked K2 and then
under that is the 092.
I have a second unit that has the output transistor marked K2 021.
These are surface mount transistors, I can not find any information on
these transistors.

Help with either problem appreciated.
Mikek

[dansabr...@yahoo.com]

Look up the SMD code of K2. This will translate into a more reasonable number for ordering.

Dan

[Phil Allison]

amdx wrote:

--------------------

> I have a CZH-05B FM transmitter.
>

** I cannot find a schem for this thing.

Can you post one ?


.... Phil

[amdx]

I can't find a schematic for my model.
The closest I have found is this.
> http://www.czhfmtransmitter.com/wp-content/uploads/2014/03/Fmuser-CZH-CZE-05BcirciutDiagram.pdf
I suspect this is a later model and the only similarity is the output
section. My unit has a couple of pre drive transistors, where the
schematic I posted the output is driven directly from an IC.
I'll see if I can make enough sense of it to draw at least the output
section.
Mikek

[amdx]

On 7/21/2017 10:41 PM, dansabr...@yahoo.com wrote:
> Look up the SMD code of K2. This will translate into a more reasonable number for ordering.
>
> Dan
>

That did get me more info, but I'm not finding my transistor.
Here is a picture, >
https://www.dropbox.com/s/rtl881nfpvc664a/K2%20SMT.jpg?dl=0

The dimensions look like an sot89 4.3mm x 2.45mm x 1.4mm.
It has a Z stamped in the middle, I was looking for Zetex (now Diodes)
but it could be someone else.

Mikek

[Phil Allison]

amdx wrote:

--------------------

> >> I have a CZH-05B FM transmitter.
> >>
> >
> > ** I cannot find a schem for this thing.
> >
> > Can you post one ?
>
> >

> I can't find a schematic for my model.
> The closest I have found is this.
> > http://www.czhfmtransmitter.com/wp-content/uploads/2014/03/Fmuser-CZH-CZE-05BcirciutDiagram.pdf

** Wow - no part numbers or component values.

How uninformative.


.... Phil

[amdx]

I think Spehro came up with the answer.

"Appears to be an obsolete Mitsubishi MOSFET RD01MUS1

"APPLICATION
For output stage of high power amplifiers in VHF/UHF
Band mobile radio sets"

Unfortunately the datasheet fails to indicate how they mark the d***
thing:
https://www.modelithics.com/models/Vendor/Mitsubishi/RD01MUS1.pdf


However this excellent product manual for the iCOM IC703 shows the
code and package for the RD01MUS1 match (page 2).
http://www.radiomanual.info/schemi/IC703_sch.pdf

Product page (no datasheet link because it's obsolete..):
http://www.mitsubishielectric.com/semiconductors/php/eTypeNoProfile.php?TYPENO=RD01MUS1&FOLDER=/product/highfrequency/siliconrf/discrete

They seem to be 'available' but from sketchy sources so who knows what
you would actually get.
sp. "
I ordered 5 pieces from an Ebay source.
Thanks, Mikek