Been trying to find a short, it shows 25-32 ohms from board ground to B+ . I've removed and replaced all the E-caps , nothing there. When I change band switch it will change from 25 ohm to 35ohm then back to 25 ohm. All IC's work, it actually tx and RX. But freq an ch don't match up. It had Chanels and unlocked Clair. I've returned it all to original. Cannot visually find any more cut components, traces or diodes. Short of pulling each part out, I am trying to find a way to isolate sections. The channel switch board does get warm, but with the short it rises from 13 to 18volts in a few minutes to a few hours. Thanks
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2000GTL short to ground
- Thread starter Sarcasm
- Start date
If freq and ch don't line up; then one must suspect the PLL, ref osc, loop osc, and output osc. That means crystals, solder joints, diodes, transistors, and E-caps. Check the TX Freq Adj VR too.
I'd be sure that your restore job didn't mess up any of the solder joints around the PLL; a common problem.
AS far as the short goes, see if it had the zener diode added to the voltage regulator. Had that problem before. The service bulletin #1226 is a solid mod; but the zener can go south.
Just for starters.
I'd be sure that your restore job didn't mess up any of the solder joints around the PLL; a common problem.
AS far as the short goes, see if it had the zener diode added to the voltage regulator. Had that problem before. The service bulletin #1226 is a solid mod; but the zener can go south.
Just for starters.
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Thanks, I think I located the short. I removed 1 wire at a time from the NB/ANL switch board. Each yellow wire made the ohms climb, until I removed the white,blue and black wires to the meter lights. Can see someone replaced them, they work. But this took away the short from the main board. So far the tr402 and resistors check good. It does have the two diodes on the back, Zener did check good, same with the srk? Diode. The switch board had four cut traces under the spkr switch. D52 was cut, r131 cut, constant 8v from 3756, tr26 cut one leg and that was pretty much it. There were 2 phone jack size wires to pll for the channels. They snapped off pretty easy, so no soldering there. We will see, if the voltage sits at 13.8 then I will continue with pin measurements and freq. thanks appreciate the reply
Are you gauging the freq offset from what you see on the built-in freq counter; or an external counter? Those built-in counters can be off and need adjusting too. I would use an external lab freq counter on TP1 and see if they move in TX mode.
**EDIT**
If the freq difference is close; then VR5 is adjusted to make TX and RX the same.
**EDIT**
If the freq difference is close; then VR5 is adjusted to make TX and RX the same.
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It TXes on a channel but the counter and ch selector don't match.what I'm chasing now before I get that far is the short. I was able to fix the speaker switch with an R&R and deoxit. I'm getting about 960 ohms across C172 and anywhere between board ground and the B+. Or 13v section. It was at 25 ohm before I cut the meter lights and LSB,AM,USB lights.now its 960 ohm. The caps are all new. If I disconnect the speaker jacks and phones , it will test good. OL or 1M ohms like testing caps out of circuit. This is when I will get proper voltage. Hook the jacks back up and it will eventually go to 2v or 18v. Sorry for the long post. My first 2000 and in no rush. Just enjoying the hobby.
You may find the 32 ohms is just the resistance of the pilot lights. They measure much less resistance when they are not lit. The 18 volts is the alarming part. Where are you measuring the 18 volts? That should only be present in the power supply section and nothing more than 13.8 volts on the main board anywhere.
It's feeding 18 to the board from the reg board. 20v from rectifier, 10 on each leg. To the sd118 then 18 coming out to the fuse then to board supply. What I have learned is when the fet301 is supplied with increased neg voltage the less positive voltage it regulates out. When tr302 the 945aq blows open it gives 18. When it shorts it does 1.9v to board. When I first rebuilt the board less the fet I have 13.8 for a short time then can watch it fall to 2v. I can pull the 945 or the fet out and stick it right back in and have 13.8 again but only last half the time. This is where I thought an E cap was bad or going bad. Not the case unless I put a new "bad" cap. If I pull a few wires off the mode switch the short is gone. One of them is to the switch board, the other goes to board right next to the yellow and purple wires on the studs next to the big cap. They feed the bias or D&F voltage. This radio had a RCA fet final in it previously. Thanks
I feed the radio with 13.6-13.8vdc and skipped the 110 supply.
8719
1= 6.54
2= 3.44
3= .33
4= 7.75
5= 7.75
6= 2.48
7= 5.35-38
8= 7.64
9= 8.04
10= 7.96
11= .002
12= .002
13= 7.9
14= 7.89
15= 7.87
16= 8.0 but settled at 7.86
17= 3.845
18= .001
The 14 pin IC nearby had 0 on all pin except .87 on pins 2,3,5,7.
The 7222 pins
1= 12.6
2= 2.7
3= 0
4= -.02
5= .03
6= 1.91
7&8= 0
9=6.12
10=11.94. The 1419 reg B=11.57 C=12.6 E=1.8
MB3756
8=.82
7=0
6=8.1
5=12.62
4=0
3=8.0
2=12.59
1=8.06
The freq now displays 96.2005-6 on AM on SSB it scans 96.****. It was rolling thru 34.6"" on last test with 18v. On AM only the on air light stays on and flickers a bit. I've only had it plugged in long enough to take voltage measurements. I did pick up 10.24 & 34.""" MHz on some test points with the scope.
8719
1= 6.54
2= 3.44
3= .33
4= 7.75
5= 7.75
6= 2.48
7= 5.35-38
8= 7.64
9= 8.04
10= 7.96
11= .002
12= .002
13= 7.9
14= 7.89
15= 7.87
16= 8.0 but settled at 7.86
17= 3.845
18= .001
The 14 pin IC nearby had 0 on all pin except .87 on pins 2,3,5,7.
The 7222 pins
1= 12.6
2= 2.7
3= 0
4= -.02
5= .03
6= 1.91
7&8= 0
9=6.12
10=11.94. The 1419 reg B=11.57 C=12.6 E=1.8
MB3756
8=.82
7=0
6=8.1
5=12.62
4=0
3=8.0
2=12.59
1=8.06
The freq now displays 96.2005-6 on AM on SSB it scans 96.****. It was rolling thru 34.6"" on last test with 18v. On AM only the on air light stays on and flickers a bit. I've only had it plugged in long enough to take voltage measurements. I did pick up 10.24 & 34.""" MHz on some test points with the scope.
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Well after replacing TR 37 a lot of the voltages are pretty good except the tx pin 8 on reg and pin 6 of pll. Drops to 1.9.
I've chased the short down to the switch board and band selector but its intermittent. When I only remove the pink (grd) wire from band selector the short goes away. So testing pin 8 of 3756 to ground, good on the board, and the band switch until I touch the pink wire back. Test the pink wire and good. So pink ground or band switch individually good and only sometimes they short when pink wire soldered back on. But I can't find a short in the selector as of yet.
I've chased the short down to the switch board and band selector but its intermittent. When I only remove the pink (grd) wire from band selector the short goes away. So testing pin 8 of 3756 to ground, good on the board, and the band switch until I touch the pink wire back. Test the pink wire and good. So pink ground or band switch individually good and only sometimes they short when pink wire soldered back on. But I can't find a short in the selector as of yet.
It sounds like the MB3756 voltage regulator may be bad. It also seems like there have been many hands in the radio and there may be multiple problems. Between the FET final, hitting the radio with 18 volts and poking around removing wires, I'd say you may need professional service before it gets too far out in left field.
Thanks shockwave, and you are right there have been many hands in this radio. I got for almost nothing. Traded a 1 pill for the 2000 & a matching speaker. I got the 1 pill for free , just had to put the pieces back together. He couldn't do anything with it. He actually put one of those swing kits in it, it does tx and RX, so I thought I'd try before I send it out. It's in pretty good condition, so I feel its worth it to restore. The more I learned about 2000's , I wanna save as many as I can. I just can't believe how badly many were butchered. I probably have a dozen chassis and they all have channels, yet no one around here uses anything but 4-5 channels in the normal band. Some look as if they had 3 or more methods cut in before they did it without cutting traces. Shame.....thanks for your help
I was wondering what the diode links are next to the finals. I think they are called link on the schematic. I have some that read open on a fluke but on a tester they have twice the forward voltage drop (1.-29-1.42) of the ones that check as a diode on the fluke. None test bad on the tester.
I am getting correct pin voltages now for a few then I'm loosing the line lock down to 1.9. I don't know why it takes 2-10 minutes to do this but I have yet to find a faulty part other than the bias driver, which only had a very low gain reading. Getting boxes ready to ship her out east. Thanks for the input on my limited info.