Marantz 2500e.. needs a bit of elbow grease
- Thread starter txturbo
- Start date
I measured the voltages:
With AGC = 2.49
Q101
G1 = .360
G2 = 1.81
Q102
G2 = 2.596
Voltage between R107 and R108 =.489
I noticed that the schematic that rBuckner supplied shows nearly identical readings except the AGC response.
Before repair shows AGC at 2.55V, after repair the range is 2.35 (strong signal) to 1.25 (off tune).
When I increase the microvolt output from the SG165 my AGC response drops. A weak signal in the RF produces 2.5V and a strong signal (10,000 Microvolts) produces 1.4V. This would support catrafter's comments on the two different AGC responses.
If I set the SG165 to 10.7 IF and inject it into the IF I lose stereo at ~200 microvolts. The AGC stays at 2.5V until I set the SG165 to the 1000X microvolt scale. Then I get an AGC response from 2.5v down to .7V at 10,000 microvolts. With the max input the scope never shows more than 1/2 signal strength.
Maybe the front end is OK and I have a problem in the IF?
With AGC = 2.49
Q101
G1 = .360
G2 = 1.81
Q102
G2 = 2.596
Voltage between R107 and R108 =.489
I noticed that the schematic that rBuckner supplied shows nearly identical readings except the AGC response.
Before repair shows AGC at 2.55V, after repair the range is 2.35 (strong signal) to 1.25 (off tune).
When I increase the microvolt output from the SG165 my AGC response drops. A weak signal in the RF produces 2.5V and a strong signal (10,000 Microvolts) produces 1.4V. This would support catrafter's comments on the two different AGC responses.
If I set the SG165 to 10.7 IF and inject it into the IF I lose stereo at ~200 microvolts. The AGC stays at 2.5V until I set the SG165 to the 1000X microvolt scale. Then I get an AGC response from 2.5v down to .7V at 10,000 microvolts. With the max input the scope never shows more than 1/2 signal strength.
Maybe the front end is OK and I have a problem in the IF?
Last edited:
catrafter
Marantz Specialist
I usually assume around 30dB of conversion gain in the tuner FE, so 6uV in (at whatever frequency in the FM band you are tuned to) would be about 200uV at 10.7mHz to the IF input. If you have another receiver, you could always sub in the tuner FE from it with a temporary coax from the sub tuner's IF output to the 2500's IF input. I keep an old FE from a 2230 for just such trouble shooting.
Tom
Tom
My cautious answer is, it sounds like it may be an IF problem. Have you attempted at least the senstivity alignments? If not, I'd recommend it very highly. Use just enough RF to move the needle to 1-2 on the signal strength meter. Adjust the variable caps for the best sensitivity at 106-108MHz wherever there is dead air to set the SG165 to. Then the variable inductors at the 90Mhz or lower end. Go back and forth until there's no (or very little) improvement.
Tom's front end sub method is a bit more work but will tell you absolutely wherein the trouble lies.
Tom's front end sub method is a bit more work but will tell you absolutely wherein the trouble lies.
Time for an update...
Jet lag..... When you can't sleep you play.
Before I left on my biz trip I took the cap out of the 2500 and brought it to work. I used an ultrasonic cleaner to get the crud out of it.
1. Fill ultrasonic with clean water and a couple ounces of windex with ammonia.
2. Preheat the ultrasonic to 50 deg c.
3. At each point where the cap shaft is grounded I put a drop of deoxit, let it soak for a moment then worked the cap back and forth.
4. Put the cap in the ultrasonic and run it for 15 min.
5. Remove and check for crud. Repeat 3 and 4 until clean.
6. Rinse with clean water.
7. Rinse with semiconductor grade IPA.
8. Blow dry with clean compressed air.
9. Using a syringe, place a very small drop of faderlube at each point where the cap shaft is grounded, let it soak and then work back and forth.
10. Let it dry overnight.
I installed the cap and tested it. I had decent, but not great sensitivity across the dial now.
I then started to play with the caps and inductors to improve the sensitivity.
I had been using a method of tuning the inductors and caps in pairs. This evening I tried the method of tuning all the inductors at the low end first then the cap at the high end as rBuckner had suggested.
So far I can pick up a station (with stereo lock) in Waco TX. from my home near Lakeway TX. According to Radio Locator that's ~76 miles away.
The last issue I am seeing is that the center tuning indicator seems off on very distant stations. Is this normal? To get stereo lock I need to tune slightly off center. On strong stations it locks in the center.
I have not tried to play with the AM yet.
Jet lag..... When you can't sleep you play.
Before I left on my biz trip I took the cap out of the 2500 and brought it to work. I used an ultrasonic cleaner to get the crud out of it.
1. Fill ultrasonic with clean water and a couple ounces of windex with ammonia.
2. Preheat the ultrasonic to 50 deg c.
3. At each point where the cap shaft is grounded I put a drop of deoxit, let it soak for a moment then worked the cap back and forth.
4. Put the cap in the ultrasonic and run it for 15 min.
5. Remove and check for crud. Repeat 3 and 4 until clean.
6. Rinse with clean water.
7. Rinse with semiconductor grade IPA.
8. Blow dry with clean compressed air.
9. Using a syringe, place a very small drop of faderlube at each point where the cap shaft is grounded, let it soak and then work back and forth.
10. Let it dry overnight.
I installed the cap and tested it. I had decent, but not great sensitivity across the dial now.
I then started to play with the caps and inductors to improve the sensitivity.
I had been using a method of tuning the inductors and caps in pairs. This evening I tried the method of tuning all the inductors at the low end first then the cap at the high end as rBuckner had suggested.
So far I can pick up a station (with stereo lock) in Waco TX. from my home near Lakeway TX. According to Radio Locator that's ~76 miles away.
The last issue I am seeing is that the center tuning indicator seems off on very distant stations. Is this normal? To get stereo lock I need to tune slightly off center. On strong stations it locks in the center.
I have not tried to play with the AM yet.
KutzlerTrans
Jennie & I with Buddy and Barney.
I would like to know, After looking at the first pictures you posted, TX, Did they find the guy that did this to the unit ??
Wow! That's some good stuff at your disposal!! Glad it's feeling better. Have you attempted adjustments in the multiplex section? There's an adjustment for the centering as well as for lowest distortion but the latter requires an FM stereo generator like your SG165 and a distortion meter.
I made some adjustments to the centering and it seems to work OK now. I have a Sound Technology 1700B that I picked up off ebay a couple months ago but I am still figuring out how to use it properly to test test for distortion. This was the first time I tried to use it.
In any case it's back in one piece again, sounds great and tunes amazingly well now. As I figure out how to use the distortion analyzer I will probably revisit it.
Thanks again for all of your help
My next task is to try and re label the face plate.