FM transmitter repair
 

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

FM transmitter repair
 

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

Dan

FM transmitter repair
 

amdx wrote:

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


** I cannot find a schem for this thing.

Can you post one ?


..... Phil

FM transmitter repair
 

On 7/21/2017 11:06 PM, Phil Allison wrote:
amdx wrote:

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


** I cannot find a schem for this thing.

Can you post one ?


.... Phil

I can't find a schematic for my model.
The closest I have found is this.
http://www.czhfmtransmitter.com/wp-c...iutDiagram.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

FM transmitter repair
 

On 7/21/2017 10:41 PM, 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/rtl881nfpv...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

FM transmitter repair
 

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-c...iutDiagram.pdf


** Wow - no part numbers or component values.

How uninformative.


..... Phil

FM transmitter repair
 

On 7/22/2017 8:24 PM, Phil Allison wrote:
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-c...iutDiagram.pdf


** Wow - no part numbers or component values.

How uninformative.


.... Phil

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/V...i/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/se...conrf/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