The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

this unit doesn`t TX or RX. When you press the mic no TX light and when you let go of the mic no RX light. Also the meter light is dead.
No RX with extension speaker either.
But the PA works fine.

When I turn the radio off and then back on the RX light comes on but then off straight away.

Any ideas as to what could be wrong?
I have changed the Audio chip with a good working one, and its still the same.

Cheers
Paul.

To help us help you please read this link
http://www.radiomods.co.nz/forum/viewtopic.php?t=312

There are 3 Grant's to my knowledge, that why its best to give us all info you can Board Number.

Rick

Sorry Rick, It was a faulty Voltage Regulator.
MB3756. I took a good working 1 from my P400 and tryed it in the Grant and it works like a dream.
I have just place an order for 1.

Thanks anyway.

Hi Rick, back to this grant again.
Board No #PC-409AC and it has the MB8719pll.
I have tryed to install a frequency mod board into it and it is off frequency by 1 channel.
eg: display shows ch 30 and when keyed up the frequency counter will show 27.295. I have changed the crystal to a 11.1125MHz as this has to be done for the mod board to work correctly.
The Mod works correctly as I have used it on a cobra 148gtl.

Also another problem, It has blown another voltage reg. What should I check to see what might be causing this to happen??

Cheers

What frequency do you have at TP1 on channel 1 and also on 40?

When voltage regulator died last time was the radio in RX or TX?

As for the voltage regulator, there are 3 or 4 possible causes of repeated failure.
Causes:
1. What is hook up to it, which is drawing a lot current?
(E.G. Has it got some toy).
2. What is the input voltage to the radio?
3. Is there a bad cap or diode on RX + line?
4. Is there a bad cap or diode on TX + line?

When voltage regulator died last time was the radio in RX or TX?

For the likes of me, I cannot find TP1 anywhere. I found it on the schematic but cant find it in the radio.

When the voltage reg failed the last time I cant say why, as I brought it like that.
And the repeated failure this time, I`m sure it happened in RX mode.
There are no toys installed, radio is a stock 4 watts and no amp running with it.
My power supply is set to 13.8V and i have tested it with voltmeter and is 13.8V.
Also the display light has never worked, but I assume this has nothing to do with it.

Is TP1 even marked on the pcb??? I`ve looked for a good hour now and still cant find it anywhere.

if your pll is a german chip you must change to japanese made pll to get proper expanding results

Mine already has the Japan pll. Also im not to concerened right now about frequency expansion. Trying to fix a problem. Thanks for the info though.

Paul,
You should be able to hook up you frequency counter to R101 (100R) or R91, your frequency counter may kill the signal, if it does then connect the counter var cap 1000pF (1nF) this should stop the counter loading the circuit.

As voltage regulator failure, check C133, C153, C154 and C174 if any of the cap are leaking it may causes the regulator failure. Is the regulator getting very hot when in RX?

Yes the regulator is getting hot when in RX. How do I check if those caps are leaking?
I still cant find TP1. I found this in the cobra 148 with no problems but in this grant I cant. Any ideas as to where it is. I can post a pic of my board and you could circle where it shouild be.

I have attached a pic of the board component side.

here is a smaller pic of the PC-409

It looks like you did not understand my last post. You can pick up TP1 at R91 or R101. See my last post.

The best way to test for bad caps are to use a cap test meter, but you do not have a cap meter just replaces them and hope for the best or do some faultfinding, (As describe
Below) it not always a cap, which is the cause of this fault but it, is the most likely one.

Basic faultfinding:
It maybe a good idea to check how much current is being drawn for at Pin1 and 6 of the voltage regulator.
If the current flowing is near to100ma in one of the two Pin?s then you need find the part of the circuit reasonable for drawing the current, you can do this by first unhook the caps and when the current level drops down then you have found the fault component.