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Marantz 2500 Refurb

Thanks for that! Lets see how they do against the Swedes tomorrow. If you look at the stats, Sweden scored more but let more in- we scored less but our goaltending was better- 50% better. Since Finland beat the crap out of the US today and they almost won against us (we won in OT) it's a crap shoot, Sweden beat Finland by a goal- it's going to come down to goaltenders. It's going to be a close game- I predict an OT game winner, Price better stand on his head if he wants that gold.
 
!~!

The Women Fought it out into overtime! i wonder what became of the woman skater that fell, but since she had inside ties, won the gold:nono:. What up wit dat?.

I just wanted to say, what a fine job you did. At $3.75 per hour, your overqualified and underpaid.:D
 
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Talk about "repair woes"! I need to do some troubleshooting in the tuner. Looks like hell trying to remove it. Then once removed, can't troubleshoot with power on! I suppose once I go through the headache of getting the tuner out of the unit, I could just replace the three mosfets, and the Q104 oscillator amp, and hope that fixes the problem. Of course, I can check the power supply resistors R106, R112, and R115. Hopefully one of those went open???? But, my question - how did you gain access to the tuner circuitry? Is there some trick or is it really the hell it looks to be?
 
Yep, it's as bad as you observed! I've said it before and will again - the 2500/2600 and to some degree the 2385, are poorly engineered. VERY poorly and this is just one of the reasons why. But sure you can power it up out of the chassis. It just needs ground and power to check voltages. The IF output coax cable can break loose at the big tuner board where it attaches, and it can still work but not as well. Guess how I know!
 
rBuckner, How many times have I muttered to myself, "bad design".....lost count. Seems most every brand out there has some mistake in it. Of course, the design engineers do not have us repair techs in mind at all! And these days, designs are geared towards ease of manufacturing, so again, no regard to repairs. One of the worst is no removable bottom plate, requiring the removal of the entire big circuit board from the unit! Often that involves removing all the screws from the rear to release the I/O connectors. I suppose it's cheaper to manufacture a unit without the removable bottom plate.
While I was waiting for a response, I decided to remove the tuner. What a hassle, but got it done. And like you mention, I connected the B+ line and ground, and was able to measure voltages. I even put my scope on the oscillator output and was able to observe the waveform, but also observed change in frequency as I turned the tuner shaft. So, the oscillator is working, thankfully, as that chip is near impossible to get! Voltages looked correct as far as power supply to the individual mosfets. I went ahead and ordered three new mosfets from Ceitron. I have ordered from them before, and have always had good luck. I'll report back here with my success or failure....stay tuned.....
 
I installed the three new mosfets today. Yes, of course, I took all precautions concerning a grounded work station to work safely with mosfets. This includes a grounded soldering iron, and grounded wrist strap. The deed is done, and I installed the tuner back into the receiver. What a trick soldering the wires back to the tuner, working in very close quarters. I think next time someone brings me one of these with a radio issue I will just say no. Not worth the headache and stress. So, the news is not good. I'm getting the familiar FM hiss, but rotating the tuning shaft, only the hiss. Absolutely no hint of any stations across the entire FM band. At this point, I think I will just return the unit to it's owner with an apology. That is, unless one of you has a last thought?
 
There's only one semi left in the front end, H104, an IC for the local oscillator. The symptom kind of sounds like it's not running. If you have an RF spectrum analyzer around (who doesn't?!) you could hang a wire by that area and see if there's any activity about 10.7MHz higher than what it's tuned for. Or lower maybe.
 
rBuckner. Thanks for the thought, but as I mentioned above, I tested that chip when I had the tuner out. I was able to rotate the tuner shaft, and watch the frequency change on my scope. I figure this is enough evidence that the local oscillator is in working order.
 
johnhoef said:
rBuckner. Thanks for the thought, but as I mentioned above, I tested that chip when I had the tuner out. I was able to rotate the tuner shaft, and watch the frequency change on my scope. I figure this is enough evidence that the local oscillator is in working order.
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Agreed! Bummer though. I've seen the IF cable center conductor snap off at the big tuner board where it attaches at the lower left corner. It still worked, but strong stations seemed weak (of course!) and not in stereo (of course!).
 
While soldering those cables back to the tuner, I had a tough time. The cables are short, creating very limited space to get not only my soldering iron in there, but the flashlight!! Then feeding the solder wire....what a hassle. The engineer that designed this sure goofed, or more likely did not think about repairs. The owner is disappointed. He contacted another repair tech and the tech told him there is no way he will work on this unit! I'm not surprised. I told him there may be one or two techs somewhere on this planet that is willing to deal with this tuner issue, but I warned him, it will probably be very expensive, not to mention round trip shipping cost! Having experienced working on this unit, I would never want to own one!
 
johnhoef said:
While soldering those cables back to the tuner, I had a tough time. The cables are short, creating very limited space to get not only my soldering iron in there, but the flashlight!! Then feeding the solder wire....what a hassle. The engineer that designed this sure goofed, or more likely did not think about repairs. The owner is disappointed. He contacted another repair tech and the tech told him there is no way he will work on this unit! I'm not surprised. I told him there may be one or two techs somewhere on this planet that is willing to deal with this tuner issue, but I warned him, it will probably be very expensive, not to mention round trip shipping cost! Having experienced working on this unit, I would never want to own one!
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Amen bruthah! I will not touch one ever again for many reasons but a main one, it's a PITA to work on most of it.
 
I'll share another story of working on one of these. That time it was a power amp issue.
The previous technician that worked on this installed screws that are too long. These are the screws that hold the output transistor circuit board to the heat sink. If these screws are too long, they touch the heat sink, and short the high voltage to ground. Then I also discovered there was no insulating washer under the screws that hold the driver transistors to the heat sink. Again, shorting the power supply voltage to ground! The original complaint was the receiver blows fuses...no wonder! I guess the inexperienced previous technician was bewildered, and finally gave up. The point here is a good lesson learned...NEVER assume the unit is wired correctly, or that components are correctly installed!! So, the amp finally powered up after this repair, come to find distortion in one channel.....This problem really aggravated me. Someone installed Q714 backwards on the power amp board!! This is something I didn't expect, so never thought to think that such a thing could occur. But as I continued with this repair, I am finding a number of mistakes that have been made by the previous technician. It took me a while to find this reversed transistor until I started doing some diode test measurements with respect to ground. That's when this showed up, showing an unexpected current where there shouldn't be one. I never suspected that transistor since it checked out OK using the diode test. This solved the distortion problem.
In general, I'll say NEVER assume anything! You never know who worked on the unit before, and what his experience is. The best lessons learned are the ones that are learned the hard way!
 
All this said, I may yet accept another one to work on, but I will be very selective. If it's a power amp issue, I'll tackle it since I have some good experience with the power amp section. Tuner? Absolutely not! Other parts of this receiver I have no experience with, so not sure. I can always accept a unit for repair, take a look inside, and then decide if I want to tackle it. I would tell the customer this will be a crap shoot....50/50 chance I will attempt a repair.
 
You speak the truth! I had something similar happen with the symptom being no bias but sounded good. Turns out the bias transistor on the heatsink was a PNP instead of an NPN. I think it was a Marantz 250 power amp. The NPN fixed it. Another model that can be iffy to fix!
 
Interesting...this falls squarely on my rule - assume nothing!! OK, a little sympathy to our fellow technicians.....we are after all human, and make mistakes. I have made plenty myself, some of them costly. But not 100% sympathy. There is a shop in the vicinity here that has unqualified technicians performing repairs. Now and then, I am brought a unit to repair that came from this shop that they could not repair. These units are often easy to repair, some are difficult. But keeping in mind the incompetence involved in the previous repair, I find errors such as your NPN-PNP error. Or in my case, mounting a transistor without an insulating washer. Assume nothing!!!
 
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