Repair Marantz M-CR603 - Page 1
Forum section: electronics / repair

author: degleve
author_rank: Contributor
timestamp: April 09, 2025, 11:03:50 am
content: Hello,I've managed to acquire a Marantz M-CR603 for twenty buck, but it does not power on.I am trying to fix it.I got the service manual from Elektrotanya.Symptoms :. When I push the power button, it does nothingRepair tries:. I am trying to understand what is the push button supposed to do. I guess it has to send some information to some IC that it has been pressed, and then activate some relay or FET somewhere to run the SMPowerSupply. However, I do not understand how this mechanism is implemented in the Marantz, and thus how to debug it. I guess this IC93 is doing part of the job ? Schematic of SMPS and the IC93 attachedEDIT. I measured 310V after first full wave rectifyingAny ideas would be welcome !

author: joel16
author_rank: Contributor
timestamp: April 09, 2025, 12:13:42 pm
content: Have you followed the troubleshooting guide in the manual (page 39 on mine)?I do not think that IC93 is getting any signal from the power button.It looks like the CPU sends a signal to Q932 to power the device on/off.I would follow the troubleshooting guide and verify all of the power supply voltages before investigating the power enable circuit.

author: degleve
author_rank: Contributor
timestamp: April 09, 2025, 12:23:51 pm
content: I didn't followed it, I assumed the problem had to be at the PS side since even powering on does not work.But you're right, I am gonna do it and keep update !!

author: joel16
author_rank: Contributor
timestamp: April 09, 2025, 01:00:52 pm
content: Doing a bit of research it looks like the power supply has a history of bad capacitors-https://www.avforums.com/threads/marantz-m-cr603-dab-no-service-problem-fix.2441284/

author: David_AVD
author_rank: Super Contributor
timestamp: April 10, 2025, 12:14:11 am
content: Not directly related, but something else to know about the Marantz M-CR603. If it powers up, but switches to Internet Radio and becomes unresponsive, it may be the network board.I have one that does this. All front panel switches were replaced to make sure they weren't causing issues. C911 and all the SMD electros on the network board were replaced too.

author: degleve
author_rank: Contributor
timestamp: April 10, 2025, 01:58:03 pm
content: After test, no tension is going out from the power supply, everyone is at a nice 0mV (I guess some pull-down resistor maintain it to ground when no signal).I guess that for the startup circuit to begin, we should at least have some voltage to CPU, no ?So I think I have to investigate the board now, but not a startup circuit, but rather some connection to it; right ?

author: joel16
author_rank: Contributor
timestamp: April 10, 2025, 02:45:19 pm
content: There is a +6V standby signal that should be always going to the CPU.On the power supply assembly I would visually inspect all of the capacitors for leakage or bulges and measure them for resistance. I am guessing you will find some bad ones.If possible, also measure capacitance, as sometimes they will not physically appear bad or measure on an ohmmeter but can still be bad.EDIT: First measure AC-L, B+, and any other upstream voltage from the switching part of the circuit.

author: degleve
author_rank: Contributor
timestamp: April 28, 2025, 06:28:46 pm
content: I am going to measure these tomorrow !thx

author: degleve
author_rank: Contributor
timestamp: April 29, 2025, 09:49:29 am
content: Okay so after measurements :. +BV are at ~320V. PD-N and PD-L are at ~120V AC. AC-N and AC-L are at ~120V ACI've tried to trace the +6V :. I do not have +6V at transformer output (TF91). So I am investigating the transformer input.. The power supply go into TF91, pin4, and I guess the pin 3 is pulled down to 0 alternatively by the chip IC91Now i suspect the chip :. When measuring TF91, 3, which is the same as IC91, 4 and 5, I was expecting to see some kind of switching. But my Voltmeter shows a neat 320V in DC and erratic values in AC so I guess the chip does not do his job. When measuring the chip power supply, I have 9.2V. I've found in the chip datasheet a mention of working voltage above 10.3V--> So maybe it could be that IC91 is not powered, and thus not switching the supply to create the +6V ?I've tried to trace the supply of IC91, but the schematics seems absurd to me. Attached is a picture :. The Vcc pin is only connected to a diode zener, a capacitor and and diode through a resistor. All of these components are grounded so where is the +9.2V coming from !? Something obvious is escaping me I feel ...Any thoughts ?EDIT : After attentive reading of the documentation of the switching chip, I think I've found the thing.Actually, the switching chip is itself charging the capacitor at the beginning in order to activate himself. Once activated, the switching occurs, and then the transformer begin to create a voltage at its secondary winding on the primary side. Thus, the chip stays on. Finally, the Zener diode is there to prevent the voltage to go higher than 20V and protect the chip from over voltage.Thus, I've measured the capacitor C902 who is supposed to charge up to launch everything : it's broke !I am simply going to replace it. Hope this could be useful to someone else !I keep you update once the modification will be done.

author: joel16
author_rank: Contributor
timestamp: April 29, 2025, 12:33:48 pm
content: D921 is a 20V zener, so either the bias voltage is not high enough, the zener is dead, or it is being shorted by another device.As I shared previously this device seems to have a history of bad capacitors. I would check those before I investigate anything else.I find the schematic confusing as well, though I do not have a lot of experience with switching power supplies. Looking at the datasheet the typical application figure shows a similar setup as the receiver. I suppose coil 3-4 induces a voltage on coil 1-2. If this is the case, then as there is no switching on 3-4 then there will be no Vcc.I would highly encourage you to test capacitors, then move on to semiconductors. If anyone has some SMPS wisdom to impart that would be great.

author: degleve
author_rank: Contributor
timestamp: April 29, 2025, 12:52:15 pm
content: Thanks a lot joel ! I've edited my last message simultaneously. Indeed, a bad capacitor hindering the powering on...I find it really strange to have such basic fault in modern equipment (some of my old amp caps are in way better shape !)Thanks for your helpI'll change it and see if it was the only failure

author: joel16
author_rank: Contributor
timestamp: April 29, 2025, 01:05:21 pm
content: Glad I could help.As to why this happens more often in modern equipment, check out this threadhttps://www.eevblog.com/forum/chat/capacitors-on-switching-power-supply-vs-linear-power-supply/

author: degleve
author_rank: Contributor
timestamp: April 29, 2025, 05:12:10 pm
content: Thanks for the link !I've hooked up the amp with the scope, but surprise ! I can see a ~300kHz noise at the speakers outputs ! Hooking a 8 Ohm load changed nothing ...This is strange no ? I mean I do not expect this from the amplifier ... I guess it is gonna be one more day of repair

author: DrijSkij
author_rank: Contributor
timestamp: May 02, 2025, 10:47:10 am
content: Quote from: degleve on April 10, 2025, 01:58:03 pmTension is a cool way to describe a voltage, or a potential difference. Very European.

author: degleve
author_rank: Contributor
timestamp: May 24, 2025, 02:54:55 pm
content: For someone who happen to read this : Turned out many cap on the SMPS were failed, I've changed them all. The 300kHz oscillations of 1Vpp in the output seem normal from this type of amplification (class D-ish here). So problem solved !