Toshiba SC-355 meter failure

Montycat

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I helped a guy out with a repair to his Toshiba SY-355 pre-amp and SC-355 power amp the other day. Essentially it most needed a fuse, 2 new meter lamps soldered in and some pot cleaning.

It all now works well except for the actual meters which don't work. The needles will move if I push them but are not at moving in response to the amp volume. I measured voltage at the PCB wires that lead to the meters and I do get voltage there, up to several volts and varying with the volume control. So it looks like the meters have died.

Other than replacement is there a fix possible? How do meters fail? From being over-driven?
 
First step would be to measure resistance across the meter leads. Getting a reading does not guarantee meter functioning; some of them have a voltage divider inside. Let us know the test result.
 
It might be an academic exercise and not possible to do any more testing. The fellow might pick up the gear before I get a chance. I'll try though.

If it was my amp I'd want to fix it but I doubt he wants to pay extra for that. They are nice little rigs.
 
I'm going to bump my own thread from 2 years ago. I have another of the SC-355 here with faulty meters. Who knows, it might be the same one?

One moves a bit and the other not at all after preliminary testing. I'll crack it open later and do some more investigation later.
 
I bought a Toshiba a few months ago with the exact same problem. The meters twitch a bit sometimes, upon power-up I think. Schematics are available on hifiengine.com for anyone who wants to follow along.
 
I too have an SC-335 power amp that had a confirmed dead meter when I bought it. Both meters actually had damage caused by a previous owners attempt at installing internal lamps. At that time I looked into meter replacements fairly extensively and found these. I ordered two so the meters matched.

http://www.andersmeters.com/VU_Meter_Reactangular__SQ10S--product--11.html

Made in the UK and nearly a perfect fit. I'm in Canada and wound up ordering through Newark Element 14. I did need to slightly enlarge the bezel opening for height but only slightly and was able to do that with a fine cut flat bastard file. There may have also been a minor modification to accommodate the barrel of the meter mechanism but again, it was minor.

With careful coaxing, the meter scales came off the original meters as well as the new ones and I swapped them over. Once installed, they look identical to the old ones.

It was not exactly cheap but it bugs me to have something that is not as it should be.

I learned something later after acquiring another SY-335 in that the meters were different. The first example, as mentioned, had lamp bulbs internal to the meters. The second used external wedge bulbs in holders mounted above the meters. If you go this route and the amp in front of you has external bulbs, you would be leaving the replacement meter's internal lamps disconnected.

A point to note is that amp has a meter level adjustment and is discussed in the service manual.
 
I'll see what I can do. I'm away from home 15 to 17 hours on workdays but should be there about 12 hours from now. Did not document the new meter install so any photos would be "after" shots.

Your meters have internal or external lamps?
 
Ok, thanks.

I think they are pretty much the same of your unit...

9315533.jpg
 
I wonder if we can possibly transplant the guts from another meter? There are more common and cheaper ones. I guess if the case can opened that might work though one would have to careful and use a model pretty close so the pointer fits.
 
I'll see what I can do. I'm away from home 15 to 17 hours on workdays but should be there about 12 hours from now. Did not document the new meter install so any photos would be "after" shots.

Your meters have internal or external lamps?
I have the SC-665 which is the 335's big brother. Wondering if those will work?
 
Interesting, the SC-665 appears to be North American version of the Aurex SC-530. Toroid trafo, fast NEC outputs...

Mine is recapped and new Zeners in it. Sweet amp. Will post some pics later.
 
I went through my memory cards and unfortunately wiped all images from the one I would have used while working on the SY-335.

If you're committed to replacing meters, accessing them is not hard and neither is removing them. Just do as I did and take photos of the process to aid in re-assembly. A set of calipers would work best to measure dimensions of the meter lens portion that protrudes through the bezel opening. Those same dimensions are indicated on the Anders website and I think you'll find that segment of their meter's lens is only 1mm or so taller than the lens opening which is plastic. The width is spot on. As mentioned, careful persistent use of a smallish, flat, fine file works well to enlarge the opening. Unless you really butcher it, it will look perfect afterwards.

If your inside the amp anyway and you're so inclined, you might find this link to another forum interesting. The outcome was so good that I performed same on two additional SY-335's.

http://www.diyaudio.com/forums/solid-state/290674-toshiba-sc335-power-supply-capacitors.html

Also refurbished their companion SC-335's.
 
Interesting, the SC-665 appears to be North American version of the Aurex SC-530. Toroid trafo, fast NEC outputs...

Mine is recapped and new Zeners in it. Sweet amp. Will post some pics later.

I live in Canada and when those Toshiba's were sold when new, they were branded Toshiba. The Aurex name was spun for upmarket products as was with Sharp - Optonica, In addition to two Toshiba SY-335's and companion pre-amps, I also have the Aurex pair SY-335 II and SC-335 II which are identical circuit wise to the Toshiba's. Only difference is cosmetics of the face plates.
 
I miss owning a 335 amp. Packed a lot of punch for it's size and if I could find a matching amp and preamp again, I would do whatever I could to get them. They would become our bedroom system backbone
 
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