President Washington 8917pll, low power and modulation

[liquidh8]

Ok guys, I've inherited another President Washington. This one the 8719 PLL.

Anyhow, it has been sitting for like 20 years. It has an expo kit in it. The USB is flaky and not working right.

I plugged it in, blew up the large filter cap in the power supply. Fixed thant, got it to make some noise, cleaned all the pot with tuner spray.

It had some odd numbered driver and finals in it, I threw in a 2166 and 1307 I had laying around.
Changed most of all the electrolytic caps.
Changed the AM regulator.
Radio is getting 14vdc.

It only does about 6-7 watts side band, 3-4 on AM. Modulation about 50-60%. Alot of the VR's oon the board seem to do nothing.

Anyone have any thoughts. Maybe a service manual for these things to give me voltage readings at different points? I have one for my 858 Washington.

Thanks Guys

Anyone have

 

[ExitThirteen]

Well, there's still some things that have to be done/changed yet for it to be 100%...

The expo kit's gotta go, those are prone to causing power and frequency issues. get it back to stock 40, you can easily change the programming on the PLL to get extra channels. This could also be why USB is acting funny.

The mode selector switch could potentially be really dirty, making USB nasty also. Unfortunately, it's a sealed switch, so you're probably going to have to "work" the switch back and forth a few times.

The 2166 is just fine, but the 1307 is part of the reason why the output is down a little... the 1307's don't work real well in the MB8719 chassis. They'll work, but they won't produce full output. If you want a little more output, put in a 1969, or a 2312.

You'll have to play around with L36 a bit to get it to come up in power. If you have done so already, then go to L28 and L29, then move to L26. Those also can change your output.

Make sure TR32 and TR25 are in place. If either or both are pulled, you can't adjust VR7, which is the SSB ALC.

Give all that a try, and let us know how you get on.

~Cheers~

 

[liquidh8]

Exit, I will do most of that tonight.
Remove the expo kit
Lock up the clarifier.
Re-align it.
Clean out the mode switch, If I have to I have a parts 858 chassis I can swipe one from.
Change the final to a 1969(i think I have one)

I already tried to adjust the cans and coils for TX power to no avail.

I'll post back later tonight.

Thank you for checkin in here!

 

[liquidh8]

OK. Here is the list of things I did.

Took out the expo kit.
locked up the clarifier.
alignment cause it was WAY off
1969 final
replaced all but 7 electrolytic caps
put a new transistor in tr32, this one was snipped
retuned the TX chain for max power
Set the driver and final bias.
cleaned the mode switch

I have adjustment of the modulation now. I am getting about 7 watts SSB, about 6 on AM.

I am told the audio sounds good, but the power is just not there. I rebuilt the power supply too since I had the parts in stock It has 14 vdc to the board. I have the voltage to the driver and final too during tx also.

Now I just have to keep replacing parts it seems till I get the TX power up to at least 12 watts SSB, lol.

Any ideas?

 

[ExitThirteen]

Is USB still acting up? Or is that good now? If it's acting up yet, you may have to shoot some contact cleaner in CT1, that's the USB TX offset trimmer capacitor. Sometimes CT1 (USB) and CT2 (LSB) can get dirty and cause the SSB modes to drop TX and/or be real scratchy.


I know some of the older President Washingtons that have the MB8719 boards tend to be low output (before they changed the name to "Uniden" Washington)... I ended up having to make a couple modifications to the S042P TX mixer IC (IC6) to bring up the output a bit. For a little more modulation on AM, change R104 (10k ohm) to a 47K ohm. That will bring up your audio a bit in AM without overmodulating.

Oh, and if you have a genuine NEC 2SC1306, install that in the driver spot and pull out the 2SC2166. The older President Washingtons that have the MB8719 boards had the 1306/1969 pair in them. This changed when the name changed to "Uniden" Washingtons, by then Uniden was using the 2166/1969 pairs.

Let us know how you get on.

~Cheers~

 

[liquidh8]

No, usb is fine also. I cleaned ct1, 2, and 3. Do have a 1306 driver also, an original one. I can give that a try.

Thank you

 

[liquidh8]

Ok, did r104, changed the driver, a few more caps. Output is still the same.

I can say the mod meter doesn't work, but the s/rf does.

 

[unit_399]

Liquidh8-

Since it looks like some screwdriver jockey was into this set, you might try removing and checking all of the cores from the cans in the RF section. I had an 858 chassis that wouldn't peak up and all of the components looked good. It turned out that a small piece had broken off one of the cores, and was stuck inside the can. Other than that I would check the mike amps (TR28/29) input and output for proper levels. BTW, you said the mod meter didn't work. Pull C183 to disconnect the mod meter circuit and see if this helps any. Good luck and 73s.

- 399

 

[liquidh8]

Unit399, I will try all those tonight. You are right about the screwdriver jockey also, lol

Also, i don't have a truth chart for all the transistors for this radio. So i don't know what voltages i should be looking for at TR28/9.


I'll post back with my findings.

 

[Zman]

Those crystal Expo kits are trash. LOL. I remove them as soon as i get a radio that has one installed. Going the PLL mod route is best...

 

[liquidh8]

Well, C183getting pulled didn't help. The mod meter still don't work. I have a mod switch, I may swap that out just to see if it helps any.

Also, i can find tr28, but tr29 is eluding me, lol.

Zman, I've com to realize that! I may just do the switch mod for the upper bands.

 

[melaza]

Hi, this is my first post.

1. Take your time and do a good visual inspection on both sides.

2. Check TR-32 (ATT) removing TR-32 can disable the ALC circuit and can cause some warbling on SSB.

3. Check TR-31 (ALC AMP)

Have a nice day.

 

[liquidh8]

Well, still never got this sorted. Wondering if one of the cans has something wrong with it?

All the transistors, driver and final are good. AM regulator. Channel kit has been removed, clarifier back to stock, aligned. Ugh.

I will be changing the mode switch too. The mod meter doesn't work, but the rf part does. I changed that transistor in the circuit, but I am missing something still. I am going to do a little more searching tonight on it. I haven't looked at the radio since my last post.

Would love to get it fixed to drive my KLV1000

 

[liquidh8]

Changed the mode switch, no go. {Cry_river}

Got the Mod/RF meter working though.

FYI, this is a different radio than the other post I made.

 

[liquidh8]

Well, the radio is aligned, and talks fine. But the radio all tuned up gets me 1-4watts AM, and 8-9 watts SSB. Nothing more. It works great, just the power is lower than I am used to seeing on the chassis'. I wonder what the deal is? There are no swing mods or nothing either on it.