1978 H. H. Scott Stereo Receiver Noisy Left Channel Issues
 

Hello everyone, I am currently working on a H. H. Scott Stereo Receiver Model 335R for someone and the symptom its having is that the left channel is noisy (popping and crackling noises) and I have worked on stereos with that issue before and repaired them, and the issue is usually with a noisy transistor in the pre-amp stage of the amplifier section (there was another name for it but I can't remember the name of it right now) and most of the receivers I've worked on before this one were pretty straight forward as to where the various transistors for each stage of the amplifier section were located but this one is a little more difficult to figure out where each stage of the amplifier section of the receiver would be located and their respective transistors.

I have downloaded the service manual for this receiver but I can't get the schematics to blow up to full screen on my laptop (Adobe Reader) and I need to view those schematics so I can find those noisy transistors.

Adobe Reader used to have a full-screen mode but that feature seems to be absent now (as I can't seem to find it anymore) and that could of been how I could of viewed the schematics easier but since there doesn't seem to be a full screen mode anymore I can't really read the schematics without having to read them inch by inch which doing it that way I can't see the full context of each circuit when the schematics are blown up to 100% just to read them, I was thinking of trying to print them off but I remembered that my printer will only print the schematics at their original 50% scale which is very hard for me to read.

Anyone have any suggestions on how I can go about making this repair using the schematics I downloaded keeping the aforementioned issues in mind?

Use the zoom tool in acrobat to zoom in just on the power amp section, you should be able to make it just the right size. If not try different PDF software

OK, I'll try that and see if that works, if not I'll see if I can find a PDF Reader software that does allow me to go into full screen mode.

OK, so I was able to figure out that the transistors I needed to replace is Q1407, Q1408, Q1457 and Q1458 which is a KSC945-Y and KSA733-Y respectively and I have some KSC1845 and KSA992 transistors which from what I was reading online should sub for the KSC945 and the KSA733 respectively but I would like to have someone double check that for me, before I try to sub them into the stereo.

You might want to check out Audiokarma! www.audiokarma.org Good luck with your receiver!

I did, I looked through a few threads and it was kind of a mixed bag, some were saying they could be subbed for each other and some were saying they couldn't be subbed for each other, and I was wanting to see if anyone could confirm either way.

In fact, some old transistors go noisy, like the dreaded 2SC458, for example. Is good to check.

The only trouble you may have is if the transistors are direct coupled in the
power amp. I would do one channel at a time & be sure every thing runs cool.
To look them up replace the K with a 2 & you got the Japan ##
The transistors are Korean, Scott labeled korean stuff in the "Quad" era. . IIRC
the last few real Scotties were quads & still built in Maynard Mass. The factory was 5 miles from my old house.

Zeno:smoke:

Gotta be careful with those Korean KSC transistors. They may be electrically equivalent to the Japanese 2SCs, but I remember the pinouts being different. You'll have to do some wire bending before installing those KSCs. Check data sheets first (NTE/ECG books are OK, you're just checking pinouts).