marantz: Marantz NR1501 typical failure - Intermittent loss of sound

Many of these model series developed the same failure after some years of usage. The sound from the inputs, analog or digital, mutes completely; sometimes selecting a different input and coming back to the original input would fix the issue for a while; power cycling, trying to service reset the unit (hold Menu+down arrow for 5 sec) may actually make things worse.

Running the service self-test (holdn Menu+right_arrow for 5 sec) revealed a problem in the HDMI/DSP board. A "CHCK DSP" error was persistent, along with intermittent "CHK CPU" errors.

 

I followed the Marantz service manual troubleshooting tips, by starting with the HDMI/DSP board power supply Vcc lines checking.

Indeed most of the power supply Vcc lines in the HDMI/DSP board were faulty; despite the multimeter DC reading being close to the specified regulator output voltage, the oscilloscope readings were telling a different story - Huge 800mVpp RF oscillation was present.

 

Just by looking into the HDMI/DSP board  gave me the reason for the issue. Those infamous SMD aluminum electrolytic capacitors are used in this PCB board - After some years of usage and aging, I expect them to be faulty or out of specification, as they usually lose the capacitance due to electrolite leakage or else the ESR rises to unacceptable levels. Also they seems to be very temperature sensitive.

 

In my unit several of these SMD capacitors showed ESR readings well above the recommended maximum  of 0.5 Ohm for the installed DC regulators. I removed some of the filter caps to test them, and found out that the ESR was around 6 to 11 Ohm (!).

 

I decided to replace all of these 40 SMD caps in this HDMI/DSP board with classical high quality mini radial 105 degree low ESR electrolytic caps, to get rid of these SMD aluminium caps for good in my unit.

Keep in mind that this unit is a high quality model, with excellent choice of components and build quality. Good old high quality radial electrolytic capacitors are used everywhere - Well, with one exception...

The HDMI/DSP board looks to be supplied by some computer company to Marantz receiver operation specification. This board looks different from the rest of the receiver, with distinct components and assemblage technology, even the PCB color is different.

 

The mini radial electrolytic caps are larger in size when compared to the original SMD aluminium, but this HDMI/DSP board has enough free space underneath. I positioned the capacitors lying flat on the PCB to ensure maximum mechanical rigidity and minimize vibration. Ugly, but efficient.

After reassembling the unit, did a system reset and run the self-test. No more errors.

I let it run for the night on the FM radio. Then played again with the input selector, tested other inputs, powered cycled the unit dozen times. 

I then powered it down for several hours to let it cool down.

Tested it once again, before finally decided to install the cabinet cover, as I could not duplicate the above errors again.

Also the sound issues were fixed.

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This tuner is from about 2009, i. e. from the early years of the RoHS directive and lead-free soldering. I remember from that time that some contract manufacturers of electronics were reluctant to using SMD electrolytics on lead-free PCB assemblies, as they were concerned that the SMD electrolytics would not stand up to the higher temperatures used for IR or hot air soldering of lead-free assemblies. I had to redesign some PCBs for one customer, using through-hole electrolytics instead of the SMD types previously used together with tin-lead solder. That customer also said that their chinese contract manufacturer could buy through-hole electrolytics for one third of the price for SMD electrolytics of the same quality. And in China at that time, the labour cost for manually mounting the through hole parts was negligible.

A few years later, concensus in the business seemed to be that small SMD electrolytics up to 6,3 or maybe 8 mm diameter had no problem with lead-free soldering, but there could be concerns with bigger cans. So there was a time where several paralleled small SMD electrolytics were preferred to one big electrolytic.

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