Grant XL having problems!!

[1jonnyz]

I just ordered the zener diodes and the mb3756, should be here Wednesday I hope.

 

[1jonnyz]

Just checked Robb and I have no TX light now and have 13 volts on TP 8 and TP9, which I assume is a voltage regulator issue?

 

[Robb]

Uh oh; this could be a big problem. Check pin #9 on the mb8719/pll and see if it is 8v. If it is 13v like tp8/9 (they should be at 8v), then the voltage reg is buggered. Hope it hasn't already taken out the pll.

 

[1jonnyz]

That is showing 9.45 volts. When I took the reading on TP8 & 9 I didn't disconnect the wires, just to let you know.

 

[1jonnyz]

I got the parts yesterday and put them in. I now have 8 volts on pin 9, which is good. I do not get any mA out of TP 8 or 9 still, and am getting about 13 volts there still. I am getting good modulation on USB and LSB, just not on AM. The meter was bouncing back and forth when I key up on AM, just for the heck of it I messed with the driver and final bias and the bouncing went away, but still no modulation.

 

[mechanic]

Check the date of the radio, can be done by the date code on the PLL IC. Radios that are getting old may need capacitor renewal. I have change quite a few caps in older gear including the Cobra 148 and Grants

73 mechanic

 

[Robb]

Remember - if you got meter movement then the mA draw had to be there. So, re-create the condition that caused the meter to move and then check the test points. You should see some reading, even if it is moving around. Or you are back to square one and have not set up your test correctly.

The only time the TP voltage could be 13v is if someone has volted the final and driver. It should be 8v there on those TP's. So either you are not reading your DMM correctly or do not have the DMM on series between the wire and the post and have not keyed the mic. That is all there is to it.

You did not say if ch 1-8 were working yet. Maybe you did, but I didn't see it.

 

[1jonnyz]

OK Robb, I figured out why I wasn't getting any mA reading on either meter... I blew out a fuse in each one, apparently VR 8 & 9 were turned wayyy up!! I did get them down where they should be. I still have 13 volts at 8 & 9. One thing that is puzzling me... on the Angelfire alignment page and the depfom page they say to put the frequency counter of TP2 while on channel 1 AM, and I should read .790Mhz. When I check it it is saying about 6 mhz?? Also when I go through the channels I do not get the 10khz shift between each one, some channels stays the same as the previous and others it jumps by 20.

 

[Robb]

The next step I would take is to see if any traces on the underside of the board have been cut at the pll chip. Also if there are any added wires leading away from the pll chip to one of the switches on the front panel. Obviously the pll and the ch switch are not dividing properly. So, either the pll is bad, there are open wires or cut traces around the pll, or the channel switch/or wiring is faulty.

In this condition, the TX indicator led probably isn't turning red; or is it?

If you are seeing 13v at TP 8 & 9 and have set the mA to spec; I would let that part go for now. Getting the pll, vco, and loop osc in sync with each other is job #1 right now.

 

[1jonnyz]

I do get the red TX light Robb. There are no cut traces and no open wires around the PLL either, although the solder on the PLL is definitely fresh. I also get the carrier that bounces back and forth between 3 and 4 on my watt meter, about 3 times a second or so. Modulation is still good on USB and LSB, no AM modulation.

 

[Robb]

I do get the red TX light Robb. There are no cut traces and no open wires around the PLL either, although the solder on the PLL is definitely fresh. I also get the carrier that bounces back and forth between 3 and 4 on my watt meter, about 3 times a second or so. Modulation is still good on USB and LSB, no AM modulation.

So SSB works - except for ch 1-8? I am beginning to think that unless you send your radio off to the shop it won't get fixed. Sounds like someone really diced it up before you got it. Is it worth fixing? Why sure! Not too many Uniden GrantXL's out there and sending it to a shop like DTB should sort it all out. Otherwise, it might take awhile to sort it all out here - at this rate.

 

[1jonnyz]

I have no problem with USB or LSB on 1 - 8.