Wednesday, 29 February 2012

Marantz SR7500 repair


This receiver had 3 different faults, which lead me to think it had been used as spare parts! A quick resistance check of the primary & secondary windings of the mains transformer and no open or short circuits (thank goodness).




http://www.hometheaterhifi.com/volume_12_4/marantz-sr7500-receiver-10-2005.html




Upon opening it up and removing sub-boards - there were the tell tale touch up solder on certain points  - quite obvious it had been looked it.

This unit had been manufactured late 2005, as stamped inside the case. It mostly consisted of through hole (leaded) components on single sided PCBs.

The DSP/CPU board however was a double sided PCB with mostly surface mount components.

image taken from http://www.nubert-forum.de/nuforum/viewtopic.php?f=10&t=16013

What really shocked me was that the manufactured build quality of this unit was far from the best I have seen. Solder joints looked dull (cold), especially on the jumper links of the single sided boards. Spent some time re-soldering these joints.

Power on issue


The power on issue was caused by a low value resistor (essentially used as a fuse - in red). I initially thought it was a faulty bridge rectifier (in green) since the resistor measured OK when not powered  up. There was also no output from the bridge rectifier. After replacing the bridge rectifier I knew straight away it was the resistor. It must have been  going high impedance when current was being drawn from it. This supplies the remainder of the low voltage rails necessary to power up the CPU/DSP section and display.



After addressing this - I was relieved to see the display and unit powered up.However it was now going into Protection mode.

Standby board

This unit uses a standby board. How this works.
1. When the main ON/OFF switch is initially turned on, this powers on a standby transformer. This is a step down transformer that provides a +5V rail to power up the main CPU.
2. A mains relay that is controlled by the CPU. This switches in the primary side of the mains transformer.
3. The CPU performs, some checks namely low voltage line checks and amplifier checks namely:
  • Over current
  • Offset voltage
  • Over temperature (high heat sink temperature >80C, amplifier running at to much load continuously)
Any one of these three conditions will cause the unit to go into protection mode.

Repairing an amplifier channel

The unit also had a blown amplifier channel. This was easy to determine by checking for short circuits across the output driving transistors. The worry with a blown channel is that it is likely to have also taken out a number of other components. This proved to be the case.
Firstly I removed both transistors from the blown channel, as it was short circuiting the audio bus voltage. I did this so I could power up the amplifier to ascertain which channels worked and which did not.

After powering the unit up and driving output to speakers, I found that the front left, front right channels and surround left and right channels were operating. I had no center, sub woofer and rear surround left and right. My initial thought was it had to be something common that affected these channels.
AV receivers have a test tone mode that you can put through each channel. I did this while probing an oscilloscope onto the channel outputs of the Electronic Volume Control IC's (Toshiba TC9482). Sure enough had the test signal coming into the Volume control IC inputs, but no output! Faulty TC9482 (circled in red below).

 image taken from http://www.nubert-forum.de/nuforum/viewtopic.php?f=10&t=16013

These seem difficult to get as they are typically only used in audio equipment.

Going back to the blown amplifier channel - rear surround left.

Using a multimeter set to measure resistance I checked a number of components and found along with the 2 output transistors (big red circles) diodes, and zener diodes had also gone short circuit, the resistor had gone high impedance.


The audio output transistors are difficult to get. Sanken SAP17N , and SAP17P, 5 terminal darlington audio output transistors.

Protection Mode


After replacing these components in the amplifier the unit was still going into protection mode.


As soon as the CPU detects one of the three conditions for protection mode the CPU switches off the main relay and thus the primary power side of the main power transformer. 
There were still problems in the rear surround channel circuit, as I had the amplifier running when I had removed the output transistors.

The next problem was how to run the unit without it switching OFF? Solder a wire across the main relay contacts on the standby board, so the main transformer stays ON!
Now I could measure some voltages without the entire unit powering OFF into protect mode.

I found a -47V dc offset at the output, and virtually -47Vdc on both ends of the AC coupling capacitor (circled in red).The output of the NJM2068 op-amp (in blue) was -11Vdc. This is what was clearly driving the output negative. It looks like when the output transistor pair blew it also took out the capacitor and op-amp input (due to over voltage). 


I'm not sure where to buy NJM2068 operational amplifiers (op-amp) from. Element14 (formerly Farnell) my local go to does not carry them.
I decided on replacing the '2068 with a On-Semi MC33078. Similar specifications on paper, and cheap enough in 1 off quantities under $2 for an audio op-amp.


Replaced both capacitor and op-amp, and removed the wire link from the mains relay on standby board. Presto - unit does not go into protection mode.
Tested each individual channel out driving it with sound - and all appears well and good. I will be keeping it even though it does not have HDMI.


Note: For new players the author does not recommend attempting to repair  mains powered equipment.Mains equipment requires care, attention and are at lethal voltages.

Disclaimer: The information contained in this post is for educational purposes only. The author accepts no responsibility for any damages or harm that may arise.

38 comments:

  1. Glad I found this blog, just snapped a faulty one of EBAY for $29, similar problem, won't power up but seller say's he can hear a relay clicking.

    Looking forward for it to arraive now to start troubleshooting the unit. I will no doubt be coming back to refer to this blog.

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    1. Thanks for your comment. I Hope you find it of some value.
      Lawrence

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  2. Maybe you could help us. Our Marantz, turns on but once its on, it immediately goes to Analog. For a split second it will go to digital. Then, it turns off. Any suggestions?

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    1. sorry Gena, like the thread below it sounds like you have a SR7500 going into protection mode!

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  3. I have a marantz sr 7500 that powers on and immediately switches off. What are my choices to address this issue?

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    1. It sounds like you most certainly have a SR7500 that is going into protection mode!

      Your options, if you have experience with servicing mains powered electronics - follow this blog.
      Otherwise I would invest in another newer receiver with HDMI capabilities.

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  4. Can you tell me where i should start my checking on an SR7400 (the most part they are the same) is start in standby but as soon as i push enter is show on the display CHECK POW5 from service manual is tells "Trouble in 5V Supply If 5V supply to DATA DIR is troubled."
    where i should check?
    thanks in advance!

    ReplyDelete
    Replies
    1. If your receiver is going into protection mode sounds like it is from what you are saying, it is most likely due to a blowen amplifier channel . The start off by checking for any short circuits on the output transistors. You will need to do this directly on the output transistors (these transistors work as a complementary pair and should be replaced together even if one device has a short circuit). Hope this helps

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  5. Hey larry, Have a marantzsr5007 lightning surge.Repaired power supply and replaced hdmi bd,all seems normal but are the output transistors supposed to be on making heat in standby mode? thanks,Ridgep

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    1. I would expect this receiver to use a standby board like the SR7500 does. Which means in standby mode the amplifier should not have power going to it and the output transistors should stay at room temperature. I would try and obtain a service manual for the SR5007 and see if it has a standby board / module.

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  6. I've spent a few hours today setting up my SR7500, but now there is a persistent buzzing sound coming from all speakers. There is just one connected speaker, no audio inputs, and have the volume very low (volume doesn't change buzz). When the receiver powers up it's quiet, 5 seconds later a single click comes from the rear of the unit, and then the buzz starts. It's in all channels and settings. Any ideas on where I should start in diagnosing this problem?

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    1. Just got off of the phone with Marantz, looks like I have an issue with the pre-amp portion of the receiver. Buzz is in all speakers, powered sub-woofer that runs out of the pre-amp output, and in headphones. Looks like new parts will be needed and may cost more than the receiver is worth:(

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    2. Can you get amplification in spite of the buzzing noise? If so I would start by replacing the electrolytic capacitors on the output of the 5V regulators on the power board (next to the big transformer)

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  7. larry,
    i know this is kind of old thread here for you, but if you see this, i have a question regarding repair of one of these 7500's. mine has this protect problem and and more prevalent than ever, although i can get the unit to power on occasionally and stay on for days sometimes. id really hate to throw it out, but repair via service is cost prohibitive.
    i also do have a little electronics experience myself and would like to take a crack myself, SO...
    if you see my message and have time to reply please shoot me a note back direct at viggi@jppc.net
    im not too proficient at blogging or social media which is why i just offer my email... i shall check back here to see if any message posted back as well. cheers!
    joe

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    1. UPDATE: i now have a Google user ID. wasnt so hard!!! ;)

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    2. joe,
      That's not a lot to go off. I'm going to need some more information.
      What happens when you try to turn the unit on when it doesn't power on? what happens when it cuts out and switches off when it goes into protection mode?

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    3. Larry,
      thanks for getting back to me. yes, was just waiting to see if heard back from you b4 explaining.
      as stated its an sr7500. problem started as an occasional protect error after running a little and then on power up. over time has gotten worse and worse, and is predominantly upon power up. sometimes will power up and then go into protect mode after running. could be a second, a minute or half an hour. sometimes will go into protect and then still power up on its own right after that as well! i also receive the occasional checkPOW5 error. so all in all is very random.
      just this week after seeing your post ive tried 2 things:
      1. disconnecting my main L/R channels from A, and connecting them to my B. at first seemed working, but then protect error reappeared
      2. i also found the master reset instructs online which i did not know about. i have done this, and unit has not failed yet but ive only cycled power and run unit several times so far. kind of funny, but could this actually have cleared its brains???! i did not expect something so simple to eradicate what seemed to be rather ominous and persistent power problem!
      Lastly, do note, i am running(and always have) klipsch towers which i believe are rated 6 ohms and not 8. dont really think that this should be any issue but thought might be worth pointing out.
      please let me know what you think of all this when you have a moment. :)
      in the meantime, think ill try and recreate the fault, go back to my A output and reconnect center and rears as well today... i'll get back to you if any news for good or bad. thanks!

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    4. Joe,
      Thanks for your feedback. It may help others that come across this blog. One cause of intermittent / erratic resetting is issues within the microprocessor / memory. So by doing a master reset as you have may indeed remedy your problem. Cheers.

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  8. Hi Lawrence,

    I have a SR7400 that switches to standby after one hour of normal use. I hoped clearing the piled up dust in the receiver would help, but it didn't. At the moment, it goes in standby after an hour, the relay clicks, the display turns off, and the standby light is on. Then it turns on again briefly, for 10 seconds or so, just a few moments of music you can hear and then it switches to standby again and stays there.

    I checked the power pcb but I can't see anything wrong there. I fixed the display though by resoldering one mount point for the connector of the transformer. The display stopped working a few weeks ago, and I guess this mount point was the special voltage supply for the display. Great to fix something that easily.

    Another thing was that the volume knob didn't work for years. I managed to fix that by cleaning the contacts in the volume regulator device itself. It was full of sticky grease.

    So I am pretty happy, but just for one hour ;) Now I just wondering how to proceed. Should I just replace the power pcb (if available), or should I try to check all the trigger points you mention above? (heat, voltage, current). Do you have a reference that I could check? The service manual doesn't say a lot about this. Any suggestions?

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    1. Ah, it just happened again and now I actually saw the PROTECT message in the display. Three times in a row with a few seconds in between and then in standby.

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    2. Hi Keesjan,
      The first two areas I would target are:

      1. If the amplifier is overheating. I'm not sure if the 7400 has this safety feature. However check if the heatsink on the amplifier is getting really hot. Better still if you have an infrared temperature probe to check this.

      2. The large output electrolytic capacitors on the low voltage regulators. If the capacitor is placed next to a hot component or heat sink this will over time dry up the electrolyte, eventually causing the capacitor to fail. I would start by replacing the largest output capacitor after the low voltage regulator (probably 5V )with a low ESR replacement.

      Good luck

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    3. Hi Lawrence,

      Thanks for answering! I was studying the service manual, went over all the triggers for the Protect mode: heat, current check on the amp output (for shorting) and input voltage unbalance detection. All these triggers go in the CPU, which decides then what to do: protect or standby.

      The heat was pretty much ok. The amp heat sink was max 45-50C. The 5V and +/-12V regulators heat sink gets to 60-65. The hottest are the rectifier bridges and the low impedance resistors near the transformer, up to 80C. But nothing really overheating. Also raising temp by covering the side vent holes, did not make it go into protect. It just happened out of the blue, even with the cover off.

      Also in normal operation and when it was in protection, this heat-detection signal was always around 5V.

      The voltage unbalance signal was also 5V all the time, both for the +/-12V and for the amp power (+/-41V)

      So the triggers either restored very quick or the CPU was going nuts. The only way to know is to continuously monitor these signal lines, but I don't have the mean to do that. I decided to clean the CPU(DSP) board more carefully, reseating connectors, after which I though I fixed it, because it ran for hours without problems.

      This morning it happened again. Few times to protect mode and then in standby. If it would be caused by a faulty electrical element I wouldn't expect it to run fine for so long. It would likely be a bad connection somewhere, so I decided to tap around in the receiver with the back of the brush I used for cleaning. As soon as I hit the top bar that holds the amp heat sink in place, at the side of the front panel, the receiver would go in standby! Then I realized I hadn't inspected the amp pcb yet, so I took it out and found a terminal on one of the big transistors nearest to the frontpanel, that was loose from the solder. I resoldered a bunch of connections that looked suspicious and hopefully this will be the end of it. Otherwise I'll try your second suggestion ;)

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    4. Hi Keesjan,
      Any luck getting to the bottom of your receiver going into protection mode and shutting down?

      In terms of monitoring heat I would also look at the temperature of the voltage regulators especially the high load ones that have a heatsink on them. It is typical for these regulators to have a thermal shutdown.

      Using a freeze spray can help locate dry / dodgy solder joints.

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    5. Hi Lawrence,

      Yes, it has been running for a couple of days now without going into protect or standby! So I declared it fixed and ordered a Chromecast Audio to celebrate ;)

      So in short I had three problems:
      1. Display wasn't working (stayed dark)
      2. Volume knob was broken (turning it did not move volume up or down)
      3. Occasional shutdowns

      I solved all of them without replacing anything, just by cleaning grease in case of the volume knob and re-soldering bad solder joints on the power pcb and amp pcb. I also cleaned dust and reseated connectors on the go, so that might have helped too.

      As for the regulators, they were at 60-65C max, so within allowable range, I suppose.

      How would you use the freeze spray? Will the low temp open up cracks that are closed at room temp you think?

      One thing keeps puzzling me. The schema shows that there is a heat signal from the CPU that triggers a relay that switches the power to the amp pcb from 41Vac to 14.9Vac. Any idea why it doesn't just disconnect the 41V?

      Btw thanks for this blog. It gave me the courage to open up the box and at least try to fix it myself. And great that it is fixed, at least for now ;)

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    6. Still working without problems :) Well that volume knob is getting greased up again I guess, but I don't care so much. Maybe I'll replace it one day. No protects or shutdowns ever since the last soldering...

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    7. That's great. Problem appears to be sorted. Intermittent problems are the most troublesome to fault find.

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  9. Hi Lawrence and thanks for the info above. I got here by searching for "SAP17 hot" :) I bought from ebay two years ago a Pioneer VSX1016V. All went fine up to some months back when I noticed that it is running quite hot, which didn't happen before. I checked with a temperature probe to see where is the hottest point and it seems that comes from one of the Darlington's from FR channel. The sound seems not to be affected at all and no distorsion. What bothers me is more related to:
    1. unusual hot temperature even if I am using it with headphones (so no power coming out to speakers)
    2. from time to time it "restarts" when looks hot, the fan (set to 60 degrees C) goes for 5-7 seconds and then it is working fine for few hours.
    Should I worry for this, or maybe I can start somewhere to fix something before something else is failing, causing bigger damage?
    I really like this amplifier and I am very happy with it.

    Thanks
    Sorin

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    1. Hello Sorin,

      If only one darlington device is getting hot, I would change both devices on the FR channel. My gut feeling is that the device in question is failing. If it was something to do with the biasing I would expect both darlington devices in FR channel to be getting hot.

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  10. Hi Lawrenny Fong,

    I'm using marantz sr5007 from last month it going protect mode.when I give power to amp it auto switch on and going protect mode

    Can you suggest you idea to rectify the issue

    Kesav

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    1. Hello Kesav,

      Firstly I assume you have some knowledge or hands on working experience with electronics.
      I'm not familiar with the sr5007 so I suggest the first port of call is to obtain a service repair manual for it.
      The places I would look at first are:

      Any low voltage supplies, especially the ones that supply the main processor board. Check the voltage is okay.

      The check the output capacitors these dry up over use. If a capacitor is near a hot component , I would be replace these.

      Check the amplifier channels by checking the output switching devices.

      Goodluck,

      Lawrence.

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  11. i have an sr7008 no speaker out no video out no setup menu buttons work but dont do much the amplifier stack seems good any ideas seems like a power supply problem it also has been reset i have the experience but lack the tools and time any help that might help narrow it down would be appreciated

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    1. what comes up on the display? no easy answers. I would start by checking the low voltage supply rails and looking at any large sized capacitor hanging off a low voltage supply. Good luck

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  12. bonjour,
    je possiede un marantz sr 7500 et du jour au lendemain, il m'affiche check pow5?????
    il s'allume sur leurrant il me met le niveau son sa dur 2 secondes et il se met en veille, et quand j'appuis sur enter il m'affiche check pow5
    que dois je faire???
    si quelqu'un peu m'aider!!!

    ReplyDelete
  13. bonjour,
    je possiede un marantz sr 7500 et du jour au lendemain, il m'affiche check pow5?????
    il s'allume (sur l' écran il me met le niveau son sa dur 2 secondes et il se met en veille), et quand j'appuis sur enter il m'affiche check pow5
    que dois je faire???
    si quelqu'un peu m'aider!!!

    ReplyDelete
  14. Hello,
    I own a marantz sr 7500 and overnight it shows me check pow5 ?????
    It lights up (on the screen it puts the sound level its hard 2 seconds and it goes into standby), and when I press enter it shows me check pow5
    what should I do???
    If someone can help me !!!

    ReplyDelete
    Replies
    1. Hi,
      First try a factory reset. If it still shows pow 5, you will need to obtain a factory service manual. Start by checking:
      The low voltage supplies
      5V output capacitors

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  15. Hello
    Thank you for your reply.
    How to reset factory? I have the manual but nothing to write the above.
    Can you tell me what to do?
    Thank you well in advance

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    Replies
    1. https://www.manualslib.com/download/701768/Marantz-Sr7500-A1b.html

      page 9 & 10

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