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|20th August 2002, 12:38 PM||#1|
Join Date: Jul 2002
Deteriorating printed circuit boards.
So I went to fire up a Marantz 2270 that was sitting in the garage for a year or so.
It worked fine the last time I used it.
This time, no go.
Looking at the circuit board underneath I noticed a lot of oxidation.
Granted, the garage is not the best environment for storing electronics BUT....
Then the same thing happened with a Sansui receiver that was working fine before.
It makes me wonder if printed circuit boards are subject to degradation over time. These units are roughly thirty years old.
I've never had this problem with point to point wired tube gear.
Could it be that early circuit boards are doomed to fail?
|20th August 2002, 12:56 PM||#2|
Electrons are yellow and more is better!
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Some pcb materials are hygroscopic (suck up moister (was it spelled right?)) Ordinary brown phenol paper pvb's are no good but it's cheap....
FR4, glass fibre epoxi is better, but not the best....
I can also imagine that some other parts have sucked in moister. Ordinary plastic transistors are not moister proof. Why does the miltary use ceramic and metal cans?
/Per-Anders (my first name) or P-A as my friends call me
Group buy Pavel Dudeks excellent LM4780 based amp No pcb's left but two not paid for.
|20th August 2002, 01:59 PM||#3|
Join Date: Feb 2001
Location: Adelaide, Australia
If it is a very old amp it may well be the electrolytics which have given-way.
Just a thought .....
|20th August 2002, 03:01 PM||#4|
Join Date: Feb 2002
Location: Perth, Australia.
Worth Fixing Marantz and ..........
I've fixed plenty of your sort of machines in the past, including ones left in the back shed for a decade or two.
"Looking at the circuit board underneath I noticed a lot of oxidation. "
Isopropyl alcohol, a white bristle art brush and tissue will clean the board so you can proceed.
Being left idle in a non ideal can cause contact problems in ALL switches and pots and connectors and switching sockets (AND trimpots).
I find/have found that the first thing to do is to use a good quality solvent/contact oil combination spray and wash out and treat all moveable connections.
Flushing the contact spray and junk out with compressed air and then re-treating a few times can restore problem ones.
Other normal failures of this vintage of audio gear are dried/leaked small diameter electrolytics (especially ones branded 'Sanyo') and dud solder joints.
When I renovate this sort of gear, I do the items listed above, and also blanket resolder the power supply and power amp stages complete, and as required throughout including pots pins, switch pins, and pcb-pcb and in/out connectors and connections.
These procedures will restore such a machine to 'as new' operation and remain ever long term reliable, and the result is well worth the effort.
Think of it as restoring an interesting and useful relic of the past and enabling a long lived future for it.
If I am really keen I will also do a blanket change of electrolytics in different circuit stages with modern low esr smps electros, and I usually regard this as a sonics improvement, however it does alter the sound to non-original.
A tip gleaned from a tube thread here regarding first time run up of old unused gear is to run it up by many brief on/long off cycles with an alligator clip lead with a series (40, 60, or 100W) lamp clipped across the fuseholder (fuse removed) to enable staged reforming of old capacitors and to limit fault currents.
These old items are usually worth preserving - decent old SS will continue to become classic and some items can command quite high prices.
With suitable improvements, most decent old gear can still be well regarded, and pleasant/comfortable to live with.
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