Batboard

Ok I have used XTVA. It charges the radio, the external speaker works fine. I ordered a NEW HHCH (yes the proper one PLN7737B) and it comes up with fail 1/90 on the display. Radio seems to receive fine in the XTVA. The radio has 7/8 host/dsp.

Any ideas.

I should add I just put a normal mic in and it TX's fine.

Jason

I have checked the ribbon cable in the xtva, tried two different radios, and tried an s-rec from a radio known to work with a hhch. I am guessing this XTVA is toast for the HHCH function or the HHCH is defective.

Anyone have a known good XTVA they would be willing to spare for a week or two so I could test it to see if its my xtva or the brand new HHCH that is bad?

Thanks

Jason

KB9KST wrote:I have checked the ribbon cable in the xtva, tried two different radios, and tried an s-rec from a radio known to work with a hhch. I am guessing this XTVA is toast for the HHCH function or the HHCH is defective.

Anyone have a known good XTVA they would be willing to spare for a week or two so I could test it to see if its my xtva or the brand new HHCH that is bad?

Thanks

Jason

Jason,

You could send me your HHCH and I can test it, 3 of my XTVA's are in vehicles, I do have one new one, but it wouldn't be new if I used it.

SG

I'd rather ship the used xtva versus the new hhch.

Jason

You could do that as well, I have a spare set of cables to hook it up with.

PM me

SG

Ok I did some looking at the service manual schematic and so forth. Here is what I found:

"The HHCH microphone has an internal microprocessor that uses
serial-data communication to the radio. The data path is put into use
by automatic switching of signal routing, performed by Q9 and U2.
The HHCH microphone draws supply current through R85, causing
Q9 to conduct and U2 to switch signal paths."

It appears my unit is not sensing the HHCH. I found that Q9 is not passing the power through to the circuit when the HHCH is plugged in. I found that if I jumped the legs of the PNP transistor (Q9) the HHCH seems to work fine. I am guessing this part is bad. The part # is 4813824A21 ( PNP, Gen Purpose ) but on MOL is no longer available.

Can I leave it as is or am I risking ruining anything????

Thanks

Jason

If it's a surface-mount component, there are SMD versions of the 2N3904 and 2N3906 (one is NPN, one is PNP). As long as the current draw is relatively low, it's not critical. These typically cost under a dime from major suppliers; you do NOT have to buy it from Motorola.

There are leaded versions of the above transistors. Another favorite is the 2N2907 (PNP) which come in both metal and plastic varieties.

If it needs more power, consider one of the TIP-series, or a 2N4918 or 2N4921 (one is NPN, one is PNP). In either case, you might as well replace it if you've gone to all the aggravation of diagnosing that part as being bad.

You might also want to check the current-sensing resistor from emitter to base. If that opened up, it would allow the new transistor to be destroyed in the same way that the current one got killed. You've found the symptom; now you've got to find the real cause. Analyze the circuit and measure the voltages on that transistor.

Bob M.

What I am hoping for is if someone (who knows what they are doing) wouldn't mind looking over the schematic in the service manual. I can email the service manual.

Thanks

Jason

I found the problem. C98 which is part #2113740F67 (CAPABLE CHIP CL1 30 470 5%) 470pF is bad. I was able to steal one from a siren unit and it now works fine.

Of course Motorola lists as item cancelled. Anyone out there have one they could send me perhaps. Its a very small surface mount device.

Thanks

Jason

it's not at all critical. In fact, it would most likely work just fine without it. It's purpose is to keep RF in or out of the unit so it passes FCC acceptance.

Surface-mount capacitors are sized in hundredths of an inch. If you look in catalogs you'll find them in 0804, 1206, etc sizes. These are 0.080 inches by 0.040 inches and 0.120 inches by 0.060 inches. So measure the old one with a micrometer, then find a similar part. Should cost only a few pennies.

Motorola will charge quite a lot for one of these parts. There's probably a replacement available if you check with Parts ID.

Since the parts are so small, if you have the room for a regular leaded capacitor, by all means go buy one of those and use it. 470pf is a very standard value.

Glad you found the real cause.

Bob M.

Well I appreciate all the help with this thread. It ends up the part wasn't bad. When it was soldered in, the robot (I'm assuming thats how its assembled) shorted the two pads where it mounts to. I had continuity across the circuit and traced it to that capacitor. I removed it, resoldered it in place, and have no straight 0 ohm continuity across the circuit anymore.

ALL IS GOOD. Time to install it now.

Thanks

Jason

Sure says a lot about their quality control in manfacturing and final test.

Bob M.

Companies just don't care anymore... The world is going to hell!