Sansui AU-919. PCB smell. - UK Vintage Radio Repair and Restoration Discussion Forum

samjmann · 27th Oct 2019, 6:50 pm

This beast of a 100W amp came my way recently. DC coupling from input to output. Frequency response of DC to 500KHZ!!! After a long period of not being used it was simply 'switched on' to my surprise it survived and has continued to be reliable. This is the first time I've ever seen this model, it gets rave reviews and would appear to be sought after. It was produced around 1978/79.

The standard of construction is that of a professional product, twin transformers, 4 FET's per channel output transistors. Rather messy from a wiring point of view, but all the heatsinks were massively over spec'd and everything runs cool.

After the usual mid-point checks and idle current, which were only a fraction out, and a lot of running to a pair of old speakers I connected it to the Shahinion Hawk speakers that have been loaned to me. I must say it's probably the best amp I've ever heard. Stereo image is absolutely spot on, it's quite a bit better at HF than the Technics amp you see in my avatar.

However...

The thing is, when it's on it smells... The smell is from the pcb's themselves, I think. I can't locate it to any one component, it just starts slowly as the amp warms up. The previous owner smoked, but it doesn't seem like the tar smell you used to get in old CRT sets when used in smokers home.

If it had been an eighties amp. I'd have simply washed each board, dried and tested. But on this there is so much point to point wiring to get the boards out, I think I could introduce a lot of intermittencies afterwards. The last thing I want is a set of short circuit FET's

Any thoughts about this one?

Regards, SJM.

Beobloke · 28th Oct 2019, 2:06 pm

Most Japanese equipment gives off a characteristic smell and it's absolutely wonderful. Hitachi equipment usually smells the best, along with Luxman, and notable mentions for Technics and Yamaha.

ben · 28th Oct 2019, 2:56 pm

Is there any sign of dust or deposits on the PCB? If so, a toothbrush with some IPA might help.

I seem to remember one trick was to bag the kit up and leave it for a while with some of those tablets you find in urinals! Think I would prefer the original smell though...

whiskas · 28th Oct 2019, 4:10 pm

As Ben suggests, I would try to get any loose dust out, but be VERY careful not to push into pots etc.
It's a very nice (and valuable) amp now - if not 100% confident in working on it, don't take any chances!
Make sure power is off and main caps fully discharged before any cleaning attempts..

Welsh Anorak · 28th Oct 2019, 5:26 pm

I agree. I'm sure we've all regretted the impulsive 'I'll just give that a quick clean' resulting in days taking remedial action!

samjmann · 28th Oct 2019, 10:36 pm

Thanks for the replies. This is a lovely sounding amp. Make no mistake I am a real HiFi sceptic, but this one is a step above the rest, by quite a way. I might do the sealed bag trick that was suggested, but perhaps not with the urinal pineapple blocks!

If the unit could be more easily worked on, I wouldn't have thought twice about giving it a bath. That said if the smell is from oils and solvents evaporating, then a wash in water may not help anyway.

Regards,SJM.

Diabolical Artificer · 29th Oct 2019, 7:34 am

You get get spray's that are supposed to neutralise odours, usually cat type smells, might be worth a try. Either that or just light a joss stick.

Andy.

27th Oct 2019, 6:50 pm	#1
samjmann Heptode Join Date: Feb 2014 Location: Nottingham, UK. Posts: 648	Sansui AU-919. PCB smell. This beast of a 100W amp came my way recently. DC coupling from input to output. Frequency response of DC to 500KHZ!!! After a long period of not being used it was simply 'switched on' to my surprise it survived and has continued to be reliable. This is the first time I've ever seen this model, it gets rave reviews and would appear to be sought after. It was produced around 1978/79. The standard of construction is that of a professional product, twin transformers, 4 FET's per channel output transistors. Rather messy from a wiring point of view, but all the heatsinks were massively over spec'd and everything runs cool. After the usual mid-point checks and idle current, which were only a fraction out, and a lot of running to a pair of old speakers I connected it to the Shahinion Hawk speakers that have been loaned to me. I must say it's probably the best amp I've ever heard. Stereo image is absolutely spot on, it's quite a bit better at HF than the Technics amp you see in my avatar. However... The thing is, when it's on it smells... The smell is from the pcb's themselves, I think. I can't locate it to any one component, it just starts slowly as the amp warms up. The previous owner smoked, but it doesn't seem like the tar smell you used to get in old CRT sets when used in smokers home. If it had been an eighties amp. I'd have simply washed each board, dried and tested. But on this there is so much point to point wiring to get the boards out, I think I could introduce a lot of intermittencies afterwards. The last thing I want is a set of short circuit FET's Any thoughts about this one? Regards, SJM.

28th Oct 2019, 2:06 pm	#2
Beobloke Heptode Join Date: Oct 2007 Location: Southampton, Hampshire, UK. Posts: 821	Re: Sansui AU-919. PCB smell. Most Japanese equipment gives off a characteristic smell and it's absolutely wonderful. Hitachi equipment usually smells the best, along with Luxman, and notable mentions for Technics and Yamaha.

28th Oct 2019, 2:56 pm	#3
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Sansui AU-919. PCB smell. Is there any sign of dust or deposits on the PCB? If so, a toothbrush with some IPA might help. I seem to remember one trick was to bag the kit up and leave it for a while with some of those tablets you find in urinals! Think I would prefer the original smell though... __________________ Regards, Ben.

28th Oct 2019, 4:10 pm	#4
whiskas Octode Join Date: Mar 2016 Location: Knutsford, Cheshire, UK. Posts: 1,495	Re: Sansui AU-919. PCB smell. As Ben suggests, I would try to get any loose dust out, but be VERY careful not to push into pots etc. It's a very nice (and valuable) amp now - if not 100% confident in working on it, don't take any chances! Make sure power is off and main caps fully discharged before any cleaning attempts.. __________________ ...where on earth did that spring/screw go??

28th Oct 2019, 5:26 pm	#5
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Sansui AU-919. PCB smell. I agree. I'm sure we've all regretted the impulsive 'I'll just give that a quick clean' resulting in days taking remedial action! __________________ Glyn www.gdelectronics.wales

28th Oct 2019, 10:36 pm	#6
samjmann Heptode Join Date: Feb 2014 Location: Nottingham, UK. Posts: 648	Re: Sansui AU-919. PCB smell. Thanks for the replies. This is a lovely sounding amp. Make no mistake I am a real HiFi sceptic, but this one is a step above the rest, by quite a way. I might do the sealed bag trick that was suggested, but perhaps not with the urinal pineapple blocks! If the unit could be more easily worked on, I wouldn't have thought twice about giving it a bath. That said if the smell is from oils and solvents evaporating, then a wash in water may not help anyway. Regards,SJM.

29th Oct 2019, 7:34 am	#7
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,662	Re: Sansui AU-919. PCB smell. You get get spray's that are supposed to neutralise odours, usually cat type smells, might be worth a try. Either that or just light a joss stick. Andy. __________________ Curiosity hasn't killed this cat...so far.