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

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

Dan

Reply to
dansabrservices

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** I cannot find a schem for this thing.

Can you post one ?

.... Phil

Reply to
Phil Allison

I can't find a schematic for my model. The closest I have found is this.

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

Reply to
amdx

That did get me more info, but I'm not finding my transistor. Here is a picture, >

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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

Reply to
amdx

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** Wow - no part numbers or component values. How uninformative.

.... Phil

Reply to
Phil Allison

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:

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However this excellent product manual for the iCOM IC703 shows the code and package for the RD01MUS1 match (page 2).

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Product page (no datasheet link because it's obsolete..):

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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

Reply to
amdx

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