Wednesday, 3 December 2014

Technics SC-CH900

Not really a repair, but possibly useful info for somebody and an excuse to share some love for the SC-CH900, for me the best, the pinnacle of the mini hifi system in the 90's. Im sure a sony MHC-6600 fan would disagree :-)



So the Technics SC-CH900, I lusted after this baby for 23 years ! I always had a fascination and interest in home electronics, hi fi's TV's etc so back in 1991 after I started work I set about saving for and buying my first stereo. I knew all about HiFi, what cable to buy etc but despite it not being 'HiFi' in the seperates and OFC speaker cable sense I was hooked on getting one of these. I think it was the copious use of VFD displays that did it. So every week I would check out the stereos in the local shopping precinct, It was between the Technics and a Sony MHC3600/5600/6600. So the time came to buy, what I actually bought was a SC-CH700, largely the same system but without Dolby surround capability or the brushed metal finish. Crucially though it was from memory about £200-£300 less than the £1000 of the 900, a lot of money for me in 1992. The CH700 did me many years of good service and I loved it but I always regretted not getting the top of the tree 900. So good old eBay delivered the goods and all these years later I have a pristine SC-CH900 and I love it.

The only issue with it was the display of the main amp unit, the other components looked as new but the amp had 2 issues, the cover / filter over the VFD was cloudy / hazy / dirty. Secondly some parts of the display were significantly brighter than other, some looked over bright, others too dim ? As seen in the picture below from just after I bought it.



I looked into getting a new display and considered swapping the display from my 700. Panasonic UK said that they did not support the unit anymore but armed with a part number from the service manual I inquired in the US and found it was still available, would have cost about £40.

I did a bit googling on VFD's and found some referance to the grid wires oxidising due to lack of use. Either manually powering them and flowing a bit more than normal current through them may help or just leaving the unit in for an extended length of time. Although the clock is lit all the time it didnt seem to be getting any better after a week in standby so I left it fully powered on overnight. Success, the next day the display was bright and uniform.

So I then stripped the unit down to clean the inside of the display, as the amp is on all the time in standby and has a fan running when the volume is turned up I suspect that is why it had got dirty and the other components looked like new.

I wasn't dissapointed with the construction, the service manuals are amazing in quality and the unit was too. It came apart very nicely, lots of screws, no forcing or plastic tabs breaking.





A careful gentle wipe and it was like new again.



All set up with my SL1210 MK3D. A video of it in action.


http://youtu.be/_xItB0q_CI0

I knew I had the brochure sat in my loft somewhere so dug it out and scanned it below, ah the memories.



A link to the whole brochure I scanned in.

https://www.flickr.com/photos/120943638@N03/sets/72157649178929430/

The only other issues I have come across with these systems relates to the fan, when the volume goes above a certain level an internal fan kicks in, if this fails the unit shuts down. My SC-CH700 did this and I fitted a new, quiter fan. The 900 seems ok so far (and I am actually just useing hte the whole thing as a pre amp currently).

The fan was my only gripe with the 700 as I found it intrusive the way it would come in and out, almost with the beat at the volume levels I listened to the unit at.


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63 comments:

  1. Matt1 March 2015 at 13:43

    The amp cutting out is due to electrical noise from the (ageing) fan tripping the protection circuit. An easy fix is to solder a 10uF (IIRC) capacitor across the fan terminals on the PCB. Note the polarity markings are wrong - they're the wrong way round. I've got a CH900 too; they're great.

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    1. Unknown6 August 2017 at 06:10

      Hi..Matt need your help..I have same problem like you...how you mean solder the cap 10uF(IIRC)across the terminal fan on PCB.Can you have photo to show me..I really need your help..

      Delete
  2. Eugenio5 July 2015 at 06:21

    Hi Lowfinger! I have the chance to purchase this system for 215 GBP. Do you this it is a bargain?
    Thanks!

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    Replies
    1. Lowfinger5 July 2015 at 08:27

      I have seen a few go around the £100 mark but most look very scruffy, even one defect on the front is going to limit appeal. Collection only on ebay adverts also keeps values of these low. I would say buy on condition alone, if it is in mint condition and you can collect / inspect it first without travelling too far then £215 may be worth it.

      Delete
    2. AK29 April 2018 at 09:37

      Hey guys. I’ve got a 900 in mint condition. Bought it brand new in ‘93. It’s given me many years of audio bliss. Alas, the display on my sound processor has suddenly stopped working. This has not affected the sound at all - it’s just a blank display. Any ideas on what’s stuffed or how I can get this repaired? Thx

      Delete
  3. Eugenio27 July 2015 at 04:10

    I´ve finally got it! It looks pretty cool despite the years, and it sounds great too!
    May I ask you something? I´m trying to connect my laptot to the system via minijack-RCA cable. The problem is that the sound is very lame, it seems it comes from the laptops sound card instead of the system´s amplifier. Do you know any solution to this? Thanks in advance.

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  4. Lowfinger27 July 2015 at 14:52

    Good to hear you got it. Although not properly impedance matched, a headphone output with the volume on the laptop turned high should give an acceptable sound. Which input on the Technics are you connected to ?

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  5. Eugenio28 July 2015 at 09:06

    I´m using the VCR input interface of the sound processor, ´cause direct connection to the RCA interfaces of the amplifier didin´t work. Do you think another pair of RCA cables from VCR output to the amplifier will work?

    ReplyDelete
  6. mowgli7 June 2016 at 07:31

    Whoever is suffering from the dreaded amp cut-off, you can still order the original replacement motor for the fan. Just search for this part number MDN4RB4MRC. I found a few in stock from a shop in Poland.
    Yes, you will see it's an electronically actuated volume controller. Fear not. You can take the casing apart very easily and just extract the motor from the volume control assembly. Worked perfectly for me and I can crank the volume to max without issue. Before it would cut-off in 2 seconds at -28db.

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    Replies
    1. Unknown20 June 2016 at 05:29

      Please send me the email id of the shop in Poland. I have the same problem with my Technics scch900. My email id is dbhube@gmail.com. Thanks.

      Delete
    2. Unknown20 June 2016 at 05:30

      Please send me the email id of the shop in Poland. I have the same problem with my Technics scch900. My email id is dbhube@gmail.com. Thanks.

      Delete
    3. gherardo29 April 2023 at 05:54

      Hello there, is this part good also for SU-CH700?

      Delete
  7. Unknown19 June 2016 at 12:08

    Impel Poland? Just ordered :) Thanks for the info! Been hunting for a year!

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    1. mowgli23 June 2016 at 02:22

      Yes sir. It's Impel. I'm glad I helped and I'm glad I found these guys, because it's a simple fix with the original part and it works great. No soldering, no PC cooling fan, none of that nonsense.

      Delete
  8. Unknown20 June 2016 at 05:21

    I am from India . I am also having the same problem of fan motor. Kindly provided me the email address of the shop in poland.This will be a great help. My email is dbhube@gmail.com

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    Replies
    1. mowgli23 June 2016 at 02:26

      Here you go: http://e-electronicspareparts.com/panasonic-variable-resistor-with-motor-50kohm-mdn4rb4mrc,9569.html
      You can look for the part number on google, there are more shops, maybe closer to India, that can send it to you.

      Delete
  9. Unknown29 June 2016 at 12:24

    My motor arrived from Poland today, and as described came attached to a worm gear driven potentiometer. It was easy to lift the small metal tabs on the housing, remove the potentiometer then disconnect the worm gear by removing two small screws. You're then left with the motor with a thread adaptor on its shaft. This pulls of with a pair of pliers. I made a note of which way around the brown and grey wires went in relation to the motor before de-soldering them. I soldered the wires on to the new motor and re-assembled the fan and its housing. The amp is now working perfectly and doesn't shut down as previously with the slightest hint of bass!! I found the fan vibrated when I first reassembled everything and this was down to the tension of the metal fan holder once screwed back down. A little bit of bending and adjustment and the fan is now pretty silent. Thank you to mowgli for the tip on this! A cheap fix (think I paid about £10 inc delivery) and saves buying a new amp :D

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    1. mowgli5 January 2017 at 08:33

      I'm glad it worked. I ordered 2 more of those motors, just in case. I plan on keeping my Ch900 for a long time ;) Cheers

      Delete
    2. Unknown28 August 2017 at 07:47

      I've just purchased my long awaited (23 years!) SC-CH900 and it has the cut off problem.
      Been reading the useful info on how to fix the problem but a little confused as mowgli says no soldering required which is exactly what I need as I haven't got one and useless with one anyway.
      But in Shane's comment it seems it requires soldering?

      Delete
    3. Lowfinger28 August 2017 at 08:08

      Mowgli, I think means no soldering onto the PCB, but the motor does sound like it needs modifying, wires soldering onto it etc.

      My advice would be to fix with the 10nf capacitor, you could buy a cheap soldering iron for a small job like this.

      Delete
    4. Unknown28 August 2017 at 08:38

      Thanks lowfinger I'll try that.
      Although a video of how to on YouTube would be of great help ;-)

      Delete
    5. Unknown30 June 2018 at 04:37

      This comment has been removed by the author.

      Delete
    6. Unknown30 June 2018 at 04:53

      You Sir are a star!!! Mine just arrived and I stared at it in horror for a few moments before returning to this thread and reading your instructions. Thank you :)

      Delete
    7. Unknown22 April 2021 at 00:00

      You guys are super heroes!
      I found a SC-CH700 including speakers in the rubbish dump 2 weeks ago. I first salvaged the speakers only for my workshop, but went back later to get the unit as well because it reminded me of the 550 my dad bought in the 90s when I was a kid. The previous owner even took the time to wrap the cables neatly with rubber straps.
      Everything was a bit dusty with a few scratches here and there, but nothing major. No dents or broken off pieces. The unit came back to life immediately and was playing music.
      The first issue I discovered was that the volume went down when cranking it up quickly - and the other way round. When turning the control knob gently everything was fine. Fixing this was a no-brainer: a bit of compressed air and contact cleaner did the trick.
      Subsequently, I found the other issues you guys have described:
      Unlike the other units, the VFD of the amp was rather dim because of the air (and dust) the fan pulled through the unit for decades. The cleaning exercise did improve things a bit but not to the level of the other displays.
      If memory serves right, I only found out about the amp shutting down at higher volume after putting everything back together. As it was "clearly" connected with the fan starting to rotate I assumed an overheating problem. I found another repair site on the internet which had the same issue with a full size Technics xxx-700 amp and suggested to check heat pipes which my 700 does not have of course. I was still certain that heat was the issues because same as this other guy I could repro the issue even with no speakers attached: the amp was shutting down past a certain volume (knob) level right after the fan kicked in.
      I was just about to take the heatsink assembly apart and to get a 5V industrial fan (that's what I was able to measure before the unit went into protect) when I came across this site. Now there was hope!
      Ordered the potentiometer from IMPEL for ~14 EUR incl. shipping. It took about a week to arrive. Took it apart as it was perfectly described above. The Technics service manual shows how to disassemble the fan assembly without breaking the blades. Just be careful with the flathead screwdriver when reaching past the blades. If you want to be 100% on the safe side build yourself a little hook that pulls the fan blades from the shaft in a perpendicular motion.
      Replacing the motor was straight forward. I did not have heat shrink tubing with sufficient diameter to get it around the motor as suggested, so I went ahead and wrapped a bit of duct tape around the motor housing for a snug fit.
      Now everything is back to normal: volume up, fan kicks in, amp keeps going. The fan is still making a bit of a noise. I suspect that its not perfectly round anymore after years of operation in a dusty environment.
      Thanks a bunch to everyone who shared their knowledge!

      Delete
  10. Oxido Perroso18 July 2016 at 17:48

    Friends, I applied the solution described replacing the engine with a new one, but my result was the same as before replacing the amplifier keeps shutting off. What I notice is that when starting the fan cut occurs. If by chance someone knows another solution to the problem is appreciated and from any information.

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    Replies
    1. Lowfinger19 July 2016 at 02:22

      Hi, solder a 10nf ceramic capacitor across the fan connector terminals on the PCB, this will fix your problem.

      Delete
  11. Unknown12 December 2016 at 15:23

    Can you please link and appropriate capacitor please Lowfinger? there's all sorts on ebay uk!

    ReplyDelete
  12. Lowfinger13 December 2016 at 00:41

    Hi, sure, here is a ebay item id 182330299305, select 10nf from the drop down on he listing.

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    Replies
    1. Unknown30 June 2018 at 05:00

      Hi Lowfinger, what voltage? They have 1/2/3 KV :)

      Delete
  13. Eugenio27 January 2017 at 09:56

    Hi, Lowfinger!

    I have a problem regarding my equipment.

    I opened it becuase the light dislay of the cd player kept going in and out every x minutes. I couldnt find a way to reach to the conections on the side of the display itself. So I reconnected and closed it.

    Damn me now the buttons from the cd player doesn´t respond at all. Do you know how can I fix this? I´ve been careful and the buses and cables seem to be in good condition.

    Any advice you can give me I´ll be very thankfull.

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    Replies
    1. mowgli5 April 2017 at 05:29

      The display going out is not caused by the display cable or the display itself, but rather the main cable plug in the back. At least that's what I found. The plug where the ribbon cable goes in wiggles a bit so moving it might toggle your display on and off. as for the buttons, you probably messed something up. You can find the service manual online. Just check the panel cable.

      Delete
  14. Unknown20 May 2017 at 09:38

    Many thanks for the advice, dodgy amp all working normally again

    ReplyDelete
  15. Unknown11 August 2017 at 05:29

    Hi I'm looking for a ribbon cable for a technics su-ch700 do you know where I can get one thanks

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    Replies
    1. Cute-Kitten22 January 2018 at 03:15

      you can solder wire connect each unit one by one, it work for me (15 wires)

      Delete
    2. Unknown24 August 2018 at 14:54

      Hi,
      I tried to connect only the amplifier and the sound processor, the equipment sounds very bad, if I connect the CD, amp and sound processor, it sounds perfect, I do not need the CD and the tape, but it seems that if I do not connect at least three modules it does'nt sound good.
      Do you know how to connect only the amplifier and the sound processor ?.
      Thanks.

      Delete
    3. Unknown25 August 2018 at 02:22


      I'm not 100% certain but I think the ribbon is designed so that the system only works with all four components connected together? However, if all you want is the amp and sound processor I'd suggest buying a cheap second hand AVR instead. In fact, even though I replaced the fan motor on my Technics, it is now connected to my Onkyo AVR via optical cable. I get the retro appearance of the hifi and its beautiful dancing equaliser with the more modern sound processing of the Onkyo AVR and a 5.1 speaker system with massive sub!!! Something to consider ;)

      Delete
  16. Unknown25 August 2018 at 02:21

    This comment has been removed by the author.

    ReplyDelete
  17. Unknown25 August 2018 at 09:27

    This comment has been removed by the author.

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  18. Unknown25 August 2018 at 09:31

    Thanks for your help.
    I have tried to locate information about this bus, but I have not found anything....
    It is possible that it works as a CAN bus, in this case it would be sufficient to put a load resistor, but I need to know the value and where to put it.
    Do you have any information about this bus?.
    Thanks.

    ReplyDelete
  19. MOLLY TECH9 September 2019 at 05:16

    INTERMITANT SOUND OR ONLY ONE CHANNEL WORKING SPEAKERS OR HEAD PHONE .CHECK MAIN POWER AMPLIFIER MICRO CHIP AND VOLTAGE REULATORS FOR DRY SOLDER JOINTS .TAKE MAIN BOARD OUT OF AMP CHECK ALL CONNECTION RESOLDER THEM ALL .

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  20. Marc5 February 2020 at 02:26

    Hi guys
    I managed to repair my CH700 amp (Was turning itself off when hot) by replacing the fan as described here, so I wanted to thank all of you who posted about this repair.
    I also wanted to ask if anyone has ever been able to repair the "sticky CD player door" issue that mine has developed lately. I've seen a few people ask about it on Google but no replies yet.
    Thanks

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    1. gherardo29 April 2023 at 06:00

      This comment has been removed by the author.

      Delete
    2. gherardo29 April 2023 at 06:01

      Hi Marc can you please list which parts you have ordered for replacement, I have the same unit with same problem. Did you replace the fan motor and added also the capacitor as well? Did you have to do any soldering?

      Delete
  21. Tom A Jones5 March 2020 at 16:36

    Hi, Have recently dusted off my old SC-CH700 system - not used for 9 yrs, but the Ribbon cable has gone it seems.. So I cannot use it or even sell it without. Is there any workaround for this cable? or has it got to be an original? Thankyou

    ReplyDelete
  22. Lowfinger7 March 2020 at 04:22

    I'm afraid it has to be the original, there are some on ebay but at predictably high prices.

    ReplyDelete
  23. Marc31 March 2020 at 04:26

    Yes. And a friend of mine assures me these ribbon cables are not interchangeable between different series either, He says he connected a CH700 cable to a CH900 and the system didn't work properly.
    I was recently quoted 290 AUD for a Bus Cable for my Sony La Scala system.(!) Thankfully they work just fine without it

    ReplyDelete
  24. Vynsparks5 June 2020 at 07:00

    I am not knwledgeable at all in Technics, and was wondering how I can read up on these older systems. For example, what is superior, the SC-C900, or the SC-DV290?

    Cheers fellahs.

    ReplyDelete
    Replies
    1. emilgeorge1234@gmail.com10 December 2020 at 01:57

      I own both.
      Ch-900 looks cool.
      Dv-290 sounds better and readily available as a 5.1 system

      Delete
  25. emilgeorge1234@gmail.com1 December 2020 at 12:05

    Please help..,Guys. does it have to be ceramic capacitor 10nf? Can I use electronic capacitors across the fans Terminals thanks!

    ReplyDelete
  26. Pes16 December 2020 at 05:52

    Hello, I'm looking for a ribbon cable for this wonderful Hi-Fi. Very difficult to retrieve here in Italy, could someone kindly address me to a site or a suggestion for a repair? One of the plastic "plug" is broken and doesn't work properly. Thank you for any suggestion!

    ReplyDelete
    Replies
    1. Marco Poto5 January 2021 at 14:54

      i search it too and i am in italy too.. :(

      Delete
    2. AK20 January 2021 at 02:17

      Hi Pes and Marco. I have a CH900 in perfect condition and in perfect working order which I am willing to sell. I also have the surround speakers. Make me an offer ...

      Delete
    3. emilgeorge1234@gmail.com10 February 2021 at 18:09

      Where are you located mate?

      Delete
  27. emilgeorge1234@gmail.com10 February 2021 at 18:10

    let me know

    ReplyDelete
  28. AK17 February 2021 at 03:21

    Johannesburg, South Africa

    ReplyDelete
  29. antig10 May 2021 at 10:59

    Does anybody know where to find the 15pin female connectors for CH700/CH900?

    I don't want to buy a whole system just to get a single female connector.

    Alternatively, does anybody has experience with clipping one of these https://www.ebay.com/itm/392520912163 to the cable?

    I want to control (power on/off) another system by hooking into the Technics flat ribbon cable bus.

    ReplyDelete
  30. antig10 May 2021 at 11:00

    By the way, what's the deal with this comment section that you have to create a GMail address (which requires a phone?!) to use it?

    ReplyDelete
    Replies
    1. mammoth5 July 2021 at 14:59

      Since when does a Gmail require a phone? It does not...

      Delete
  31. Vocalist Alj24 June 2021 at 09:56

    I have a technics SU CH900 powers up everying works but no sound although "TEST" works and the volume be increased just nothing out of the cd tuner tape etc
    Ive checked slow blo all fine
    Any ideas?

    ReplyDelete
  32. Anonymous4 April 2022 at 07:11

    This comment has been removed by a blog administrator.

    ReplyDelete
  33. gherardo29 April 2023 at 06:05

    Hi Lowfinger I have a SU-CH700 unit, will the same parts be fit as well? I have the power cutting-off issue, so I will have to replace only the fan motor (which is a panasonic component I understand). Do I need that only or also the capacitor? Do I need to do any soldering?

    ReplyDelete
  34. Bloggermx14 June 2023 at 05:37

    I got a ch900 a couple of months ago, great system and I am super happy with it. But yes... Same problem too... It shuts down at high volume. I don't have experience with electronics and soldering, i was wondering if some of you is located in Berlin and would not might to help ¿? Beers on my part ofc

    ReplyDelete
  35. Marco Poto3 December 2024 at 10:38

    Sir can you please write down the display part number? I will want to buy for my 900

    ReplyDelete

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