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P800 rebuild problem

drmazzei

drmazzei

Member
I am rebuilding the P800 power board for my Marantz2275. I have replaced C801-802, C804-809 with new UPW electrolytics. I have replaced R-807, R-815, R-816, and R-817. H-808 and H-811 replaced with MUR1620. H-801 and H-804 replaced with KSC2073TU. H-802, H-803, H-805, H-806, and H-807 replaced with KSC2383YTA. When I power up the receiver with a dim bulb tester, R-801 smokes. I have looked at the schematic diagram and tried replacing H-808 and C810 with no change in results. I'm not an electronics expert and unsure as to what is causing this resistor to burn. What do the experts suggest is the cause of this problem? Thanks in advance for your assistance.
 
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Probably not the problem, but a better sub for 2SD330 and 2SD331 is MJE15030G. The originals had a max collector current of 2A. The 2073TU has a max collector current of 1.5A. I just hate using less robust subs if there is a more robust one available. Have you tried running it with both power amps disconnected? That would help eliminate the possibility one of them is drawing too much current.
 
I replaced my 2sd330 with TIP41C and it works extremely well. Double check the wattage rating on your resistors. Some of the two watt resistors will run hot. Post a picture of your power supply so you can get more eyes on it.
 
Steven Tate said:
Probably not the problem, but a better sub for 2SD330 and 2SD331 is MJE15030G. The originals had a max collector current of 2A. The 2073TU has a max collector current of 1.5A. I just hate using less robust subs if there is a more robust one available. Have you tried running it with both power amps disconnected? That would help eliminate the possibility one of them is drawing too much current.
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Greetings, Dr. Tate, I am in the same profession as you are and "practice" electronic restoration on the side. Since I'm not an electronics expert, what do you do to disconnect the P700 power boards as suggested?
 
drmazzei said:
Greetings, Dr. Tate, I am in the same profession as you are and "practice" electronic restoration on the side. Since I'm not an electronics expert, what do you do to disconnect the P700 power boards as suggested?
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Welcome to the asylum! On the 2275, each amp board has a white connector with several wires. These wires include the power to the board. You can just unplug them and power up. If your resistor is still getting hot, it probably is on the P800 board, and you would need to go back and check all of your work for polarities, solder bridges, transistor orientation, etc.
 
So, I've been working on and off on this P800 board and checked polarities, checked soldering, checked transistor orientation, and changed H801 and H804 to TIP31Cs. I added a heat sink to H801. I finally have been able to bring the 2285 up on the dim bulb tester without smoking the R-801. Now, when I check the output at J804 and J805, I only get a reading of about 6V DC. I have the white connectors to the two P700 amp boards disconnected. I get the same results when I plug the receiver into a regular power outlet. I also removed the resistor that was attached on the backside of the board since I'm not sure if it's an add-on and what it's function is. Any suggestions from the experts would be appreciated as always. P1010244.JPG P1010245.JPG
 
Check the voltage at the collector of H801 and H803. Also, check the voltage at the emitter of H803.
 
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I guess you are not also getting 13.4V at pin 806. In that case, dual diode H808 is open. If you are getting 13.4 volts at J806 then check the solder connection of R801
 
You can check continuity between one end of R801 and R807 to the middle pin of the dual diode to be sure. You can replace H808 and H811 by MUR1620CTG
 
Also, check the connections with the transformer at pin J801, J802 are okay and the pin J805 has a good connection with the chassis ground.
 
Here's the update. I checked continuity btwn R801, R807, and the middle pin of the dual diode and all was ok. I also checked the grounding of J805. Then I decided to replace the H808 that had a MUR1620 already with another of the same exact type. After checking connections, I powered with the dim bulb and blew up C807. After rechecking connections again and replacing C807, I managed to fry R801 yet again. I have two more of the MUR1620s from a second P800 board, but I'm weary of installing a bad dual diode. Is there any way of checking these components before installing?
 
These are common cathode dual diodes. You can check with a component tester or with DMM with a diode check function one lead at the middle pin. What wattage of the bulb you are using with DBT?
 
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