2275 restore
- Thread starter rossm
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That's pretty dry! What do the power supply capacitors look like?
That's typical for compound that old. I would still clean the heatsinks to get rid of any dried compound
Blue Shadow
Waiting for Vintage Gear from this century
That may have been the right amount to use back then. The compound is only there to fill the surface roughness of the sink, mica and transistor. The metal to mica contact is so much better at heat transfer, using too much compound is a bad thing.
True, too much is worse than none at all. However, dried compound is also ineffective. Hence, needs to be cleaned off.
Mike Sweeney
Well-Known Member
Also, on the 2285B, the hardware has a flat washer, a lock washer and bolt. Unlike the smaller brothers. There is considerable debate but the short version is that the washers help distribute the clamping load more evenly which in turn increases the efficiency of the transfer of heat. Does it matter? Probably not but, for myself, I replace the hardware since it's 40 plus years old and been heated and cool who knows how many times with new stainless hardware.. and I use the washers. Its pennies to buy the parts off the auction site. I found a good vendor who sells reasonable quantities at a fair price. And what looks like a lot of goop is just a slightly oversized mica. The coating is pretty thin. The image is from a 2245 I'm working on right now. No washers when I took it apart but it has them now with new hardware.
Those transistors are rated for 250 watts total device dissipation at 25° C, so I think you'll be fine.
HI
I have been making progress on the restore, I do have one issue now and that's 120hz hum from the speakers. The hum is only present when the volume is turned down and does not increase with volume. I know its not coming from the main power amps because I can connect iphone to the power amp rca jacks on back and hum goes away. Started looking for hum in the power section for the preamp which is board P800. I did notice the voltage on J804 is about 43v (should be 35) tried adjusting VR 806 but only changes output by .2 volts. I have replaced all electrolytic caps on 800 board as well as the dual diods H808 and H811. I am seeing some noise with the scope. Will have to recheck my work tomorrow, have not touched H801, H802 or H803. Any suggestions welcome.
I have been making progress on the restore, I do have one issue now and that's 120hz hum from the speakers. The hum is only present when the volume is turned down and does not increase with volume. I know its not coming from the main power amps because I can connect iphone to the power amp rca jacks on back and hum goes away. Started looking for hum in the power section for the preamp which is board P800. I did notice the voltage on J804 is about 43v (should be 35) tried adjusting VR 806 but only changes output by .2 volts. I have replaced all electrolytic caps on 800 board as well as the dual diods H808 and H811. I am seeing some noise with the scope. Will have to recheck my work tomorrow, have not touched H801, H802 or H803. Any suggestions welcome.
Hi Tom,
Good call, I had some time tonight to poke around and I found that when I was replacing caps I had accidentally un-soldered one of the legs of H809 and then forget to solder it back. Rookie mistake haha......
I have noticed another small issue, only when the turntable is unplugged I can hear a vary faint hum when the selector is on the phono settings, I have read that diodes H408 and H408 can be noisy. Think I will replace them tomorrow.
The scope is cool, I have never used digital scope before so it takes some learning, Its pretty deep and has a loud fan so I have been looking at some of the newer low end scopes on the market..
I have the caps to recap the am/fm tuner boards, problem is I have never done radio alignment, so If something goes wrong, my only option would be to backtrack an put the old parts back in. I have 1 week to finish this project and ship it out.
Do you guys typically replace caps on the tuner boards ?
I measure all parts that I have removed and most everything removed so far has been pretty close to spec.
Mike Sweeney
Well-Known Member
Yes I do.. it's not a complete job in my mind if you don't. And I still use FM radio for stuff like classical music, NPR and some sports. And I have yet to "have to" re-align after replacing caps. I've had several radios work noticeably better after the caps were replaced but not re-aligned. And yes, the AM/FM boards are a PIA
Steven Tate
CEO Flat Forehead Soc.
Concerning the hum on the Phono input, be aware that the metal bottom cover is part of the shielding/grounding system in Marantz systems. If you are testing with the bottom off, be sure and test it with bottom on before diving into parts replacement. The hum will likely go away
catrafter
Marantz Specialist
Also, many times flipping the AC power plugs over on either the receiver, the turntable or both will lower or eliminate the hum. That's why the plug ends are non-polarized.
Tom
Thanks, I will take a look at that soon...
I was able to recap P200 board FM IF amp successfully and turned my attention to the P300 Stereo Decoding Amp. That looks like its going to be a bear... I removed the screws but was only able to move the board about 1 inch, barely enough to see the back, I removed the left channel amp/metal guard and tried to find some slack in the wires to get more play but its pretty tight, any suggestions on this one ???
I see in another thread thxdave had to remove wires from this board to get room to work, was hoping not to have to do that..
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Steven Tate
CEO Flat Forehead Soc.
First thing I do is look under the chassis for those tight wires to see if there is a nylon tie that might release a bit of length if removed. But sometimes, you just have to remove a wire. You can cut and splice, but not very pretty. You can remove the wire wrap connection and put it back later with a conventional joint - not very original looking. Or you can desolder the pin and remove it from the PC board with wire wrap. That looks the best, but getting those square pins back in the holes is sometimes a challenge.
