Hi, picked up a Model Twenty Eight and need some help cleaning it up and getting it to sound as it should. I took out the unit from the case and cleaned it up with compressed air and deoxIT. The sound across all inputs is muddy and distorted, especially in the left channel where it comes in and out. I assume some of the resistors and/or capacitors are bad. I have the manual. I just want clarification which resistors and capacitors I should check and if needed replaced.
Can someone help me troubleshoot which ones need to be replaced?
Thanks.
Can someone help me troubleshoot which ones need to be replaced?
Thanks.
Not so easy. You'll need some test equipment, what do you have?
There are likely to be multiple problems.
https://www.hifiengine.com/manual_library/marantz/model-28.shtml
There are likely to be multiple problems.
https://www.hifiengine.com/manual_library/marantz/model-28.shtml
Ok, but this should be viewed as a significant project, on a lower end receiver.
Post a bunch of photos, top and bottom. Was this from a smoking environment?
Post a bunch of photos, top and bottom. Was this from a smoking environment?
I recently helped a friend repair his Model 22. All the preamp transistors were shot, making the whole thing hum and noisy. 2sc458 transistors seem to be particularly bad, but there’s lots of recommendations out there for what to replace them with. I think we used either KSC1845 or BC550.
And just a few general troubleshooting tips:
- While there is a problem, don’t change parts in the hope that you’ll magically cure it. Try to identify the things that need fixing. Take a good look at the circuit board, ideally under a magnifying glass, and look for burned or bulging things.Also Google for known problems.
- adhere to the EEVBlog first commandment: thou shalt check voltages. Try to find test points and see if the voltages match what’s marked on the schematic.
- Don’t touch it if you’re not sure. This is mostly for the radio section of these receivers. They can get thrown off calibration quite easily if you start replacing things.
- take lots and lots of pictures before you start. Things like transistor and capacitor orientation are so easy to mess up so having pics makes double checking your work a lot easier.
Yes, consider the complete tuner section to be "off limits".
And if you do end up replacing any transistors, some of them may have to be installed
on the pcb in a different manner from the originals, with the package twisted or the leads bent.
And if you do end up replacing any transistors, some of them may have to be installed
on the pcb in a different manner from the originals, with the package twisted or the leads bent.
I will use my voltage meter first to see if I can detect any issues. Figure #11 on the manual is difficult for me to follow. Does the row on the top with all the H items correspond to items within the schematic? Also, how can I find out the proper voltages?
I am also tempted to sell it as is.
I am also tempted to sell it as is.
In each section that corresponds to a PCB (dotted lines surround it) what you call "H items" gives component number, Marantz part number and common part number for the solid state devices. The voltages are indicated on the schematic.
I haven't worked on a Model 28 but have done many Marantz receivers, including 22, 26, 27. These are decent receivers, although the next series (22xx) are better. This should be easy to work on because it's well laid out ad boards are accessible. It's unlikely that a resistor is causing problem you describe. Could be a capacitor but could also be an active device. It certainly wouldn't hurt to replace all the electrolytic capacitors. Be sure to follow the recommendations already included in this thread. Pay particular attention to the orientation of the electrolytics - almost all are polarized. Marantz made a lot of in-production changes and so best guide is to replace the capacitor with like capacitance and voltage. I'd recommend doing just one capacitor at a time. There is no guarantee that replacing the electrolytics will solve the problem. I'd start with power supply and then go to amp section. Be sure to use a DBT after any work - will save serious problems. Test after each board. There are only 3 boards that are likely to cause the problem you describe: amp; tone (preamp) and possibly PSU (although that's unlikely culprit).
Cheers.
I haven't worked on a Model 28 but have done many Marantz receivers, including 22, 26, 27. These are decent receivers, although the next series (22xx) are better. This should be easy to work on because it's well laid out ad boards are accessible. It's unlikely that a resistor is causing problem you describe. Could be a capacitor but could also be an active device. It certainly wouldn't hurt to replace all the electrolytic capacitors. Be sure to follow the recommendations already included in this thread. Pay particular attention to the orientation of the electrolytics - almost all are polarized. Marantz made a lot of in-production changes and so best guide is to replace the capacitor with like capacitance and voltage. I'd recommend doing just one capacitor at a time. There is no guarantee that replacing the electrolytics will solve the problem. I'd start with power supply and then go to amp section. Be sure to use a DBT after any work - will save serious problems. Test after each board. There are only 3 boards that are likely to cause the problem you describe: amp; tone (preamp) and possibly PSU (although that's unlikely culprit).
Cheers.
Nothing jumps out to me. All appears to be factory and no visible signs of failure (not all failure is visible externally, however).
DBT is dim bulb tester - lots written about how to build and use so I won't repeat.
DBT is dim bulb tester - lots written about how to build and use so I won't repeat.
Thanks. Can you just talk me through how to rest the voltage so on H401. I put the red cable on on the wires and the black one on ground, right? Where is the ground? Sorry for my novice questions?
You should get a copy of the service manual on HifiEngine - it will answer most of your questions.
I have it but I don’t know how to test if a component is bad. I have a voltage meter but don’t know where to put the red and black pins to test each one.
All you can do without removing component is to test voltages at points shown on schematic.