Sony KV-1370R (Grey)

SuntharAbout 3 min

Sony KV-1370R from 80s

You’ve acquired a beautiful 1365R or 1370R, only to find the audio isn’t working. Luckily, the fix isn’t too complicated if you have the schematics and the service bulletin Sony issued in August 1987. However, as always, the devil is in the details.

Sony 1370R Composite

When I first tackled this problem, I referenced the schematics and purchased transistors I believed were suitable replacements. What I learned was an important lesson: the audio amplifier circuitry in these old sets, which uses both NPN and PNP transistors, requires matched transistors. This means it’s not enough to just get transistors with the correct part #; the NPN and PNP transistors must also have matching hFE (DC current gain) values for the audio amp to function properly.

As you can see in the video, I eventually got it working after a few attempts. I’m happy to have restored the audio on this beautiful TV. I’ve always loved the aesthetics of these sets. I was driving back from Quebec City this summer and glad I made the decision to pick this up on my way back for $50 Canadian.

Keep in mind, not all 1370Rs are affected by this issue. There was a revision made to 1370R later in the 80s. Later revision chassis had an audio fault, which is something we will delve into this article. This audio issue also affects 1365R CRTs as well. So, if your audio is functioning, there’s no need to replace the components. Only consider this fix if your audio isn’t working.

Warning

It's important to note that the KV-1370R operates with a hot chassis setup, meaning the ground isn't isolated on the low voltage side. Consequently, modifying it for RGB input is not straightforward.

Taking this set apart Sony 1370R

Sony KV-1370R (grey) specs

Manufactured: Made in Japan
Tube: A34JBU10X, Made in Japan
60 Hz AC: 120V 97W

Back Label Sony 1370R

Tube Sony 1370R

Schematics Sony 1370R

Area of Focus Sony 1370R

Components that must be changed are maked in yellow. Optional changes are marked in green. When addressing this issue, it's important to replace all the related components. The burnt resistor is what caused the transistors to fail in the first place. Sony 1370R

Component	Original Specification	Replacement Specification	Notes
Q252, Q250	2SA1013	KSA1013Y	Failed transistors
Q251	2SC2383	KSC2383Y	Failed transistor
R255	1/6W, 82 ohms carbon	1/4W, 82 ohms metal film	This resistor will be burnt/open
R254	270 ohm carbon	Short using a jumper
C250	4.7uF, 50V	3.3uF, 50V film capacitor
C254	10uF, 160V electrolytic	10uF, 160V polymer	Optional replacement
C252	4.7uF, 100V electrolytic	4.7uF, 100V polymer	Optional replacement

After replacing the components Sony 1370R

I opted to replace the audio capacitors with film and aluminum polymer capacitors to enhance reliability. This is optional. Only replace capacitors if they are out of spec.

Components replaced Sony 1370R

Replacement kit Sony 1370R

If you are interested in purchasing this kit checkout my storeopen in new window.

Video showing the difference between using matched vs unmatched transistors in the audio amp. The difference in audio quality between matched and unmatched transistors is significant. When the hFE values aren’t matched, you can hear the audio distort and rattle. This issue is common with older audio amplifier circuitry, whereas modern audio amps are designed to avoid this flaw.