Hello everyone. This is the first Marantz that I have worked on. I have spent some time over in the Pioneer forum and I have gained some experience there. So far I have successfully recapped a SX-737, SX-950, and an SX-1010. I still have a lot to learn about troubleshooting, and I could use some advice from the forum members here to help repair this model 27.
I have done a bunch of searching here about the model 27 and it seems that this is not one of Marantz best offerings. This unit belongs to a friend and it was originally his dads so in spite of the model 27’s reputation it would be awesome if I could get the unit working for him again.
I was told the unit would only cause a hum when hooked to speakers.
I plugged the unit into my DBT and the bulb stays dim. I checked the offset and found 26 volts on both speaker output channels. I also checked the bias and both channels had 0 volts.
I removed all 4 output transistors and tested them with the 6-way test. All 4 outputs tested fine, but at least two of them have been replaced before. The replacements used are NTE. It looks like R539 and R541 were also replaced. The installation of R539 was especially bad. The new resistor was soldered to the cut leg of the old resistor. This solder joint fell apart when I tried pulling the other leg to test. Because of this I am not 100% sure if this resistor was actually in the circuit completely before my work or not. I do not see any evidence that any other parts were replaced during the previous repair.
I pulled and tested H503 - H514 from the amp board. H503 is shorted between the emitter and collector. H513 shows open on all 6 tests. The other transistors all passed the 6-way test.
I pulled one leg of diodes H515 - H518. These all tested fine.
I pulled one leg of resistors R539 - R542, and R547 - R550. Other than the poor installation of R539 these resistors all check fine.
This is where my abilities get limited. Would an open H513, and a shorted H503 cause the lack of bias and large DC offset that I measured? Are there any other parts that I should still check? Can/should the op amps H501 and H502 be tested?
I have done a bunch of searching here about the model 27 and it seems that this is not one of Marantz best offerings. This unit belongs to a friend and it was originally his dads so in spite of the model 27’s reputation it would be awesome if I could get the unit working for him again.
I was told the unit would only cause a hum when hooked to speakers.
I plugged the unit into my DBT and the bulb stays dim. I checked the offset and found 26 volts on both speaker output channels. I also checked the bias and both channels had 0 volts.
I removed all 4 output transistors and tested them with the 6-way test. All 4 outputs tested fine, but at least two of them have been replaced before. The replacements used are NTE. It looks like R539 and R541 were also replaced. The installation of R539 was especially bad. The new resistor was soldered to the cut leg of the old resistor. This solder joint fell apart when I tried pulling the other leg to test. Because of this I am not 100% sure if this resistor was actually in the circuit completely before my work or not. I do not see any evidence that any other parts were replaced during the previous repair.
I pulled and tested H503 - H514 from the amp board. H503 is shorted between the emitter and collector. H513 shows open on all 6 tests. The other transistors all passed the 6-way test.
I pulled one leg of diodes H515 - H518. These all tested fine.
I pulled one leg of resistors R539 - R542, and R547 - R550. Other than the poor installation of R539 these resistors all check fine.
This is where my abilities get limited. Would an open H513, and a shorted H503 cause the lack of bias and large DC offset that I measured? Are there any other parts that I should still check? Can/should the op amps H501 and H502 be tested?
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