I bought this thing about 20 years ago. Has a very sharp and crisp picture as is typical of those trinitron tubes. It sits on a pedestal that has controls for on/off vol +/- and channel +/-. The controls are in the base and very large. You use your feet.

Anyway it's no sound/no picture. Didn't smoke anything when it died. Might be a nice project to bring the thing back to life. Not that there is any shortage of projects.

Should I add it to the project pile? Worth messing with? I used to work on TVs way back when so I'm no stranger to the insides of a TV.

If you're lucky, its as simple as resoldering the 12v standby transformer. There could also be problems in the switching power supply or perhaps a bad HOT. However if you didn't see any smoke or hear any pop - it can't be all that bad.

They did have great pictures, and as long as the grayscale and tracking was still good before it failed - FIX IT!

If you're lucky, its as simple as resoldering the 12v standby transformer. There could also be problems in the switching power supply or perhaps a bad HOT. However if you didn't see any smoke or hear any pop - it can't be all that bad.

They did have great pictures, and as long as the grayscale and tracking was still good before it failed - FIX IT!

Hey, thanks for the advice. There was no smoke or sparks or shooting flames. It just kind of died gradually so solder joints might be problem. I'll check out the supply.

I have not tried to troubleshoot it. Will be 'another' winter project. :D

I have and adapter that turns it into a CGA monitor too. Whoo-Hoo.

What's the model #? I can't think of any pedestal-mounted controls on a 27", but I know the KV-25XBR & KV-25DXR with those; both the early fine-pitch 25" Trinitron tube.

The DXR is a digital TV, which can be a nightmare to work on, but it had a really great picture. The XBR is nice to work on, but beware that I found many failed flybacks on those. If the B+ fuse is blown, and the horizontal output is shorted, check the solder connections on the horizontal drive transformer (very near the horizontal output transistor) before replacing the transistor, as it could blow the new one immediately or in a month, if there are cracked connections.

Charles

What's the model #? I can't think of any pedestal-mounted controls on a 27", but I know the KV-25XBR & KV-25DXR with those; both the early fine-pitch 25" Trinitron tube.


Thanks Charles!

You are correct sir! I was just at the other house and re-checked. It is not a 27" but a 25" KV-25XBR. (and I edited the original post).

I've got a High Voltage meter from the 'old days' I'll dig it out.

So i guess the horizontal output transistor can suffer the same fate as the HO tube on old tube sets. I've seen the tube envelope melt and form a nice little funnel. I also burned the heck out of my forearm brushing up against one.

Any idea where I can put my hands on a service manual? Maybe Sams?

Thanks Charles!

You are correct sir! I was just at the other house and re-checked. It is not a 27" but a 25" KV-25XBR. (and I edited the original post).

I've got a High Voltage meter from the 'old days' I'll dig it out.

So i guess the horizontal output transistor can suffer the same fate as the HO tube on old tube sets. I've seen the tube envelope melt and form a nice little funnel. I also burned the heck out of my forearm brushing up against one.

Any idea where I can put my hands on a service manual? Maybe Sams?

Definitely I don't recommend Sams for any Sony sets, but I guess if you don't find a Sony book, it's better than none. Or, if you have the original owners' packet, there's a folded schematic in there.

To start, you can do a few quick checks without the manual:

Check the fuses; a glass pigtail (soldered-in) 1.25 or 1.5 amp fuse, and a 4 amp or 5 amp fuse (same type). One is likely blown, and that's due to a short in either the horizontal circuit, or the power supply module. I'm a bit foggy on the physical layout of that set, but if I recall, the power supply is mainly squeezed in a cage below the CRT neck, and between the two hinged swing-out boards. Find the horizontal output, (should be a T03 case on a fairly big heat sink), and it should say H OUT on the heatsink. Also check the little green ceramic disk, which goes from collector (to emitter, I think). That can short and burn. Usually you can see a black hole in it, if it did, and it will measure shorted when disconnected. If that set has the horizontal output mounted off the board, follow the leads to the sweep board, and the horizontal drive transformer should be right there. Often there are cracked solder joints at that transformer. It's location # T401 in a lot of Sonys. Also, that set may have a high voltage divider block, which is mounted up on the metal X-ray shield of the CRT. Those go bad too, and load down the power supply. However, usually they won't blow the fuse. They just knock the set into shutdown, and you hear a squeal. An equally common possiblity of a cause of a short/blown fuse, is the flyback. Sadly, I have to say it's a strong possiblity, especially if the other things check out OK. One more remote possiblity, is that if the AC line fuse is blown, check the degaussing thermistor. Those can either short or get bad solder connections, causing the line fuse to blow. Follow the degaussing coil leads from the rim of the CRT shield to the board, and look for a 1/2" black cube with 3 legs on the board, right where that degaussing coil plugs in.

Naturally, there are all kinds of other causes for power supply problems, but the above is what I've seen most on 80s Sonys, including that 25XBR.

Charles

Charles,

Thanks for the info. That gives me a lot to go on. I'll try and find the Sony service manual.

I'll post more when I actually open the set up and get down to business. Likely to be a while though.

I've worked on a number of those. If the horizontal output transistor is bad, look for bad connections on the transistor itself and follow the base foil to the driver transformer. It can have connection issues also. If the HOT is bad, the chopper (switch mode) supply has shorted transistors and the .1 om resistor is open. Be careful as the main electrolytic(s) can still be charged and ruin your day. Change the two chopper transistors and the resistor and slowly bring it up on a variac. Check for heating (CAREFULLY, The sink will bite if you get between it and ground) of the chopper transistors. If they get hot look for a burned resistor (1/4 watt) going to the standby supply. Use a magnifying glass and you will see it. It usually is green bodied. I can't remember the value but it is a common color code type resistor and usually enough remains to find it's value out. Once the set is up and running, watch for heating on the HOT and choppers after about three to five minutes. If hot, add heat sinks as some of the generic replacements tend to run hot and fail after about three hours without the added heatsinks. Keep us posted!