Uniden Washington MB8719 PLL won't align

[Deleted]

The clarifier on this was hacked, so I fixed it according to several websites that have the unlocked clarifier instructions. However, I cannot align it. The 10.240MHz freq is low. When I go thru the procedure, and cannot adjust any of the frequencies to spec (all seem low). Is this PLL toast?

I do have a scrap 8719 and several 40 channel mobiles with 10.240 crystals. Any advice?

[Sonwatcher]

Did someone add channels ? If so they may/may not have changed a crystal per channel mod instructions-

"Locate and unsolder the 11.1125mhz Crystal and replace it with a 11.3258 mhz crystal."

You may want to see if this has been done .

[Sonwatcher]

A lot of people did it themselves. Not hard to do .

[Deleted]

I did locate the crystal and it is a 11.3258 MHz. I'll be d**ned.

[Sandbagger]

Dec 31, 2008 18:52:58 GMT -5 @vinnies said:

I did locate the crystal and it is a 11.3258 MHz. I'll be d**ned.

That crystal is usually changed to shift the range of the PLL's extra channels to more above 40, as that is what most people want. The stock crystal stops at channel 44 but goes way below channel 1.


That crystal change will not cause the problems you are having. I have seen 10.240 crystals slip off frequency. I had a couple radios where the channel dial was off a whole channel, and it turned out that the 10.24 was the culprit.

You can play with cap values (C64, C65) to try to bring the crystal back on freq. Also be careful adjusting the 7.8 Mhz carrier oscillator crystals. If they are off too much it will affect your transmit audio frequency response on SSB (You could sound too muddy or too tinny). When adjusting the 11 Mhz crystal, you need to set the CT3 trimmer on USB first, and then set L19 and L20 on LSB and AM respectively for the proper frequency offset.

[Deleted]

You nailed it Dave. Took a scrap heap crystal, popped it in, and boom, it worked.

When I try to align, I still have problems:

USB 34.9855 (should be 34.9875)
LSB is OK at 34.9825
AM is 34,9838 (should be 34.980)

You think the PLL is bad?

Also:

USB is OK at 7.80249
LSB is OK at 7.879749
AM is way off near 20MHZ. SAMS says should be 7.800. My guess is the SAMS seems wrong.

Also, I forgot to mention this. Some moron turned up the power supply voltage to 17.5 V. I turned it back to 13.8V. Not sure, but I think there is a misconception that turning up supply voltage give you more power. Anyway, could this have screwed up the PLL?

[Sandbagger]

Jan 1, 2009 10:58:49 GMT -5 @vinnies said:

You nailed it Dave. Took a scrap heap crystal, popped it in, and boom, it worked.

When I try to align, I still have problems:

USB 34.9855 (should be 34.9875)
LSB is OK at 34.9825
AM is 34,9838 (should be 34.980)

You think the PLL is bad?

Also:

USB is OK at 7.80249
LSB is OK at 7.879749
AM is way off near 20MHZ. SAMS says should be 7.800. My guess is the SAMS seems wrong.

Also, I forgot to mention this. Some moron turned up the power supply voltage to 17.5 V. I turned it back to 13.8V. Not sure, but I think there is a misconception that turning up supply voltage give you more power. Anyway, could this have screwed up the PLL?

Ok, a couple of things..... First off, the PLL is NOT bad. It's a digital divider chip, and as long as it is maintaining lock, it's fine. The fact that you have some frequencies off is more an indication of other crystal maladies.

The 7.8 Mhz carrier oscillators are a bit tough to set on AM. On SSB, you can set them on receive as they are on for both TX and RX. But on AM, they are only running on TX, and with the RF of the transmitter floating around, you can interfere with the frequency counter's probe and get erroneous readings. You also have to set CT1 for your USB frequency first, and then set L17 for the AM carrier freq next (in the TX mode). What I sometimes do to make this a bit easier, is to disable the transmitter driver and final by pulling the wires from TP7 and TP8. That way you'll have better luck getting your counter to lock to the 7.8 Mhz when transmitting on AM.

[Deleted]

I was able to adjust this 7.800, but it was a pain. Still no change on the PLL alignment.

The schematic did have a 11.1125 crystal, but I verified it was changed to 11.3258. Is it possible that that is off?

[Sandbagger]

Jan 1, 2009 18:06:02 GMT -5 @vinnies said:

I was able to adjust this 7.800, but it was a pain. Still no change on the PLL alignment.

The schematic did have a 11.1125 crystal, but I verified it was changed to 11.3258. Is it possible that that is off?

Catch me up a bit here. What specifically is "off"? Are the channels lining up wrong, or is the channel frequency off from the .5 center channel frequency? Or is it something else?

[Deleted]

Forget what I said. I found the culprit. The 20K clarifier pot is open. I quick visual shows it is scorched on the inside.

I have a spare from a scrap 148. Before I screw this up like the other guy, the wiring colors are different than the clarifier mods on the web. This is the way I was going to do it.

One end of the pot to 8VDC
The other end to ground
Wiper goes to anode of D35

Correct?

[Deleted]

That was it. Aligns like a charm. Clarifier slides.

I am having trouble reading thr 7.800 MHz AM transmit adjust. It's all over the place, even with those 2 test points disconnected. That is the last adjustment in the PLL alignment. All other worked like a charm. Go figure.

[Sandbagger]

Jan 1, 2009 20:27:51 GMT -5 @vinnies said:

Forget what I said. I found the culprit. The 20K clarifier pot is open. I quick visual shows it is scorched on the inside.

I have a spare rom a scrap 148. Before I screw this up like the other guy, the wiring colors are different than the clarifier mods on the web. This is the way I was going to do it.

One end of the pot to 8VDC
The other end to ground
Wiper goes to anode of D35

Correct?

Yea. But remember to remove R187 if it's still connected to D35 or you'll have a synchronization problem between TX and Rx.

[Deleted]

I did romove both, and works great. But I cannot get a fix on the 7.800MHz am transmit adjust. It is all over the place. Any advice?

[Deleted]

Never mind. I cheated. I measured at the antenna for 27.18500. Was much easier.

[Sandbagger]

Jan 2, 2009 9:20:24 GMT -5 @vinnies said:

I did romove both, and works great. But I cannot get a fix on the 7.800MHz am transmit adjust. It is all over the place. Any advice?

Yea, cheat. Oops you did that already....... ;D

[Deleted]

Dave,

This radio is finished. I lowered the DK to 3 watts. I was unable to get 100% modulation with R104 at 10K, so I tried a few resistors. Seems the 18K did a great job keeping the modulation at about 110% throughout the varying amplitude of the input signal, without clipping (mic gain at max).

Also, the I got scratchy reports on SSB. I found the ALC way up to 16 watts peak, and turned it back to about 12. Reports were great afterwards.

I want to thank you and everyone on this board for your help. 3 techs had this radio before, and couldn't figure it out. But I have you guys as a cheat sheet. My friend is thrilled because I do it for nothing (I do it for learning, and not for making money). I spent about 2 days on it.

[Sandbagger]

Jan 2, 2009 12:31:48 GMT -5 @vinnies said:

Dave,

This radio is finished. I lowered the DK to 3 watts. I was unable to get 100% modulation with R104 at 10K, so I tried a few resistors. Seems the 18K did a great job keeping the modulation at about 110% throughout the varying amplitude of the input signal, without clipping (mic gain at max).

Also, the I got scratchy reports on SSB. I found the ALC way up to 16 watts peak, and turned it back to about 12. Reports were great afterwards.

I want to thank you and everyone on this board for your help. 3 techs had this radio before, and couldn't figure it out. But I have you guys as a cheat sheet. My friend is thrilled because I do it for nothing (I do it for learning, and not for making money). I spent about 2 days on it.

No problem. That's what we're here for.

I can remember when I first started tweaking and fixing radios back in the 70's. There was no CBtricks, or internet forums to "cheat" from, so we all had to learn the hard way. But our pain is your gain. I enjoy "giving back" to those who share the fun of radio, especially the old classics...........