superscope, unfamiliar component

[beamnet]

Hi,

I have a very nice sounding superscope R-1220 reciever.

Just now, the right channel lost allmost all it's volume and sounded distorted.

After all the regular checking an measuring, I decided to play it with the lid off.

There was an unfamiliar component glowing orange inside.

I marked it with a green dot on the attached pic.

Anybody knows what it is and if i can replace it?

Thanks a bunch!

[jacco vermeulen]

Euhhh, i'd say it's a LED or a Mini-Me naughty bag.

[benchtester]

I can't see it well enough to guess. It might help everyone if you could identify the identification number on the board. In particular if it starts with an R it is a resistor, C is a cap and Q would be a transistor.

[anatech]

Hi beamnet,
I'm pretty sure that's a lamp. That is from memory as I have serviced many in the past. Not so many these days.

Your Superscope is a nice little receiver. They look nice when clean. They were a less expensive line to the Marantz line that Superscope distributed.

Anyway, on to repairing this. You have excessive current flowing through the lamp. Do not run the receiver any more. You need to repair the faults. I have never had to replace one of these lamps, so I can't help you with the type number. Probably a 40 mA bipin of some kind.

If you are not familiar with repairing equipment, proceed with extreme caution. It would be a shame to see this nice little set die needlessly. If you send it out for service, look for a tech who is familiar with Superscope. That tech will be 45 ~ 65 years old most likely and may work from home by now.

To service, test each and every transistor in that channel carefully. You need a good transistor checker, like a Heathkit IT-18 (measures both leakage modes). May as well replace the capacitors by now. Measure all the resistors in the output/driver section. Replace them even if they are only discoloured. Use a variable power supply or variac (variable AC transformer) to power it up for testing. This will prevent further damage. Don't even try to power it up until you have replaced the blown components.

-Chris

[beamnet]

Thank you anatech!

I am fairly confident around electronic.

My guess was a lamp too. Could it be that the one NOT glowing is broken?

It's a shame I don't have a good transistor checker...

[anatech]

Hi beamnet,
The lamps do not normally glow. An open filament is possible, but not glowing is normal for that circuit.

You need to either pick up a good tester (you will use it, believe me) or build some testing jigs. A bad tester is worse than not having one. The IT-18 goes for $10 ~ $silly money on Eeek Bay. The IT-18 is fast and accurate. There are others just as good, but they generally take much more time to use. Could be my prejudice here since I've used an IT-18 since they were new (in the 70's). I love mine and have a spare in case it breaks. I did buy mine new and it wasn't cheap. They only had factory wired ones left at the time. I did build an IT-121 about five years ago. My father found that unbuilt kit on Eeek Bay.

One of the more important tests are the leakage tests. A rough guide to beta is required, but the leakage tells you if the transistor is going bad before it fails. It does miss some, but catches most iffy parts. The missed ones are probably my fault for not heating each one up as I test it.

-Chris

[unclejed613]

another, more accurate way of telling if a transistor is getting ready to fail is noise testing it. apparently transistors begin to get noisier as they get ready to fail. NASA has been using noise testing methods since the 70s. a transistor increases its noise production as it gets to the last 10% of its life. if you could build a noise test jig for transistors, you could compare a suspect part against an average of known good parts. somewhere here i have the article from a NASA engineer on how they discovered this, and their testing methods.

[anatech]

Hi unclejed613,

another, more accurate way of telling if a transistor is getting ready to fail is noise testing it.

They do get noisier, but I disagree that that test is more accurate. It is also more difficult to implement that test. The noise is due to leakage currents mostly. Measuring leakage is easier and allows you to put a number on it. That depends on how sensitive the test is, you may need to know what normal leakage is if you are measuring germanium transistors or your test is very sensitive.

Heating and cooling the transistor package will show mechanical die defects or wire bond issues. Heat will cause much more leakage. Cold will cause moisture (or impurities) to become more conductive and increase leakage.

The wear out period for transistors operating well within their limits is so long that the wear out hours are not known very well. Nor is the end of life failure mode. If you read early GE or RCA documentation, they look at leakage as their indicators of transistor quality. The noise is a secondary effect. An oscilloscope may be the better tool as an indicator in that case anyway.

-Chris

[unclejed613]

IIRC Superscope was a Sony product line...., just like Technics is a Panasonic product line

[phase_accurate]

IIRC it was indeed Marantz.

Regards

Charles