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.

Panasonic SA PT470 dead, no power.

A Panasonic home theatre system, passed to me as dead no power.

A close listen revealed that the unit was not totally dead, pressing the power button the unit would click on then immediately off (but nothing on the display). This could be repeated a second time but then the unit would not respond. Pulling the power lead would allow this sequence to be repeated.

So the unit was alive and intelligent.

A quick google gave me the manual to download from the excellent site, electrotanya.

http://elektrotanya.com/panasonic_sa-pt470.pdf/download.html

Panasonic / Technics manuals are absolutely superb.

I may do a post about my beautiful Technics SC-CH900 that I finally bought after 22 years ! :-)  anyway..


So I opened it up and stated to take a look. Nothing obvious so decided the best plan of attack was to take the PSU out to get some proper access.

Admission: I took a stonking 360v dc hit from the main cap, Warning,  always approach with caution, measure the high voltage DC caps, and discharge as appropriate.

This fault will leave the main caps charged. I usually check but got sloppy.


So nothing jumped out visually, the mains went through a hefty filter and feeds standby power section of the PSU, the main psu is switched in through a relay, the relay only stays in if the PSU behaves correctly.

I did some passive checking but again nothing jumping out.

A move not without risks but I decided the best way forwards was to bypass the relay and see what wasn't powering up, the brain was obviously not happy and shutting everything down.

Using the drawings I checked all the rails and found the 18v fan power to be absent. I checked the rectifier diode D5805 and found it short. Fitted a repalcement and all good.

BMW E83 X3 PDC fault finding and sensor replacement. 66206989069

The PDC enables as you engage reverse and you are met by a long tone and then no PDC function, indicating there is a fault.

To check the sensors the engine does not have to be running, just but the ignition to second position so the dash lights up and press the PDC button. The long tone will sound. You can now get out to check the sensors.

Put your ear close to each one in turn, you should hear a very faint ticking sound. Any that don't are bad or have a wiring fault. In my experience the sensors do just go faulty, that is ones that look pristine and have clean electrical connectors can just stop working.

Order a replacement sensor. 66206989069 from ebay, £10 delivered

I had a search of the web about removing and refitting the sensors and didn't find a lot of encouragement, some indication of having to remove the bumper.

I can tell you on a model with unpainted bumpers it is possible to replace the rear inner sensors without having to take the bumper off because this is the one I did.

To replace the RHS inner sensor.

Remove the tow hitch cover.

Reach you hand in the gap to the back of the sensor.

Feel for the plug, squeeze and remove the electrical connector, this is in line with the body of the sensor but at the top.

The sensor can now be removed, tricky working blind but quite doable.

The sensor is held into the bumper receptacle with two fingers. Splay the two fingers downward and pull the sensor out. Theses fingers hold onto plastic pips on the sensor holding it in place. The fingers are quite flexible, my tip is to grip the body in the palm of your hand, splay one finger downward and pull on the sensor at the same time, then while still maintaining a pulling force on the sensor (this keeps the pip out of the finger ), splay the other finger. The sensor should then start to pull out from the rear.

Slide the new one in paying attention to the orientation.

My faulty sensor. New one in and all working ok.