Sanyo AVM-3659G Problems

[dnpainting]

Hello,
New to this forum and i wanted to see if anyone could help diagnose some problems.

I am trying to repair this TV for my brother in law. He told me that his son had turned on the TV and the screen flashed and nothing else happened. The tv has been unplugged for a good 6 months, one month while I have had it. Before I even plugged it in I did some probing around and discovered that the HOT has shorted out. I removed the board and unsoldered it to be sure and it has gone out. I am going to start removing a leg from everything in the Horizontal circuit to test, caps, transistors, resistors and diodes. I also wanted to find out how I can test the FBT?

One final question: The Transistor that is bad is a 2SD1880, I was looking for a replacement and wanted to see if this is a good one to use.

[dnpainting]

I have located and ordered the original Transistors at B & D Ent.

[radiotvnut]

I don't recall seeing that many flyback failures in these later model Sanyo's; but, it can happen. When a HOT shorts in one of these, it's usually due to bad solder connections and/or bad electrolytic capacitors in the horizontal driver circuit or in the B+ line that provides voltage to the horizontal output circuit. In a few cases, I've seen the switching power supplies run away with themselves and send hundreds of volts over the B+ line to the horizontal output circuit. When this happens, it usually burns up a whole bunch of stuff all over the chassis and makes the TV not worth repairing. The best way to test a flyback is with a piece of equipment called a "ringer". The older models, like what I have, require that the flyback be removed from the circuit. Later models allowed for testing while the flyback was still in circuit. Back in the late '90's, a friend had about $10K worth of Sencore equipment that would do this.

I've also placed an ordinary 100W incandescent light bulb in place of the B+ fuse (or, fusible resistor if the set does not have a B+ fuse). The light bulb will act as a load and will help prevent damage, in the event of a short.

When ordering a new HOT, you might want to order 2 or 3 of them. If the fly is bad, the new HOT will often short instantly. That's why I check everything carefully before applying power because I don't like blowing up new parts if I can help it.

Once you get it going, check the B+ for the proper voltage. It's usually between 120V and 130V.

Here's a video I made of me using a light bulb in place of the B+ fuse and testing the flyback in an '82 Sylvania. I realize it's an older TV of another brand; but, the concept is still the same.

http://www.youtube.com/watch?v=IV4M7SqmAqo

[dnpainting]

Thank you radiotvnut,
I have a dim bulb tester and a variac. Should I remove the fuse and connect the DBT to the fuse socket (Fuse is still good by the way) or can I plug the TV power cord into the outlet of the DBT and the DBT to variac, variac to wall outlet?

I have ordered 4 of the transistors, just incase. Also, my brother in law has had work done on this tv before. He said that the TV tube was changed. He thought it was the tube again that went bad. When I took out the board and turned it over to unsolder that transistor, that was the only solder joints that had a bunch of solder flux left on it. All other joints were clean. I think this part has been changed before and only part that has been changed. The amount of dust that was on and around the TV tube was a lot thicker compared to the amount on the board. Even the front control board had more dust than the main board. The tube was supposedly changed about 2 yrs ago, but, who knows.

Thank you again

David

[radiotvnut]

I'd remove the fuse and connect the bult to the fuse terminals.

[dnpainting]

Thank you Radiotvnut.

I've been testing the capacitors but I am not sure if these are 10% or 20% caps. I pulled a 470uf/200v out and it tests at 406uf. There have been a couple others like this. Do you think I should just replace?

Also, I don't have schematics for this TV, I only have other models that i am just using as kind of a board layout type, most caps seem to be the same on my board, but not all and same with the resistors.

Does anyone happen to have these schematics?

[dnpainting]

OK, have a slight problem, maybe. My wife deleted all my pics of the wire connections on the board. All are connected except the Deguassing Coil Connector. Does it matter which way the connector goes on? it will fit both directions.

Getting ready to run a DBT to the fuse holder (No fuse) with a 100 watt bulb.

Thank you

David

[dnpainting]

Connected to each side of the fuse holder with a 100 watt bulb and got nothing as far as bulb lighting and then going dim. Bulb did, however, get warm. I then put the fuse back in and plugged into my DBT with the 100 watt bulb and it seemed to be triggering the power circuit, It would click, and click constently making the light bulb come on and go off. Like it was struggling to get the power it needed.

I had checked every resistor, diode, transistor and cap in both the HOT and the power supply and everything seemed good.

I am going to try a 150w bulb now

EDIT** Same Thing with 150, constently. Seems, not enough power???

[dnpainting]

Plugged into full power and what do you know, got sound and snow picture (No antenna or cable connected). No smoke and no burning smell. Need to connect DVD to see picture after I check B+ voltage.

[radiotvnut]

Sounds like you may have it fixed. Just monitor the temperature of the HOT heatsink after it's been on a few minutes. If it's too hot to touch, you likely have problem and the HOT will soon fail again. If it's comfortable, let it run and check it again in 30 minutes, then after an hour, and so on. It will get hotter the longer it stays on; but, if it gets too hot to touch, you may have other problems. And, it doesn't matter which direction the degaussing plug is inserted.

[dnpainting]

Thank you for all your help. B+ voltage is at 129v. Ran the tv for a good hour on DVD and heatsink and part is warm but not hot. When I removed the old part, the compound behind transistor was probably the original, hard as a rock and just crumbled. This part had either new solder on it or maybe the TV Tech just reflowed it, but did not change the compound.

Alls seems to be good!

Thank you again!

David

[dnpainting]

I forgot to post pic of the TV working again. I am going to re-cap the power supply as they are testing about 14% of spec.

Sorry for bad pic, taken on my cell phone.

[dnpainting]

Well, I ran the tv for a good 6 or 7 hours here in my garage. All was good. Delivered to brother in law and he connected it up and watched tv for hours. Then today, he said his daughter was watching it then the screen went black and unit was making a buzzing/static sound. They unplugged it for a while and plugged it back into a different outlet, same thing, no picture, just a buzzing and static sound. When they told me it went out again, I told them to just unplug it.

When the tv was here, I checked voltages, replaced the caps that were on the lower side of specs, checked diodes, resistors and transistors.

Any thoughts on the cause? I don't have the tv with me anymore but will probably have it back in a week or so.

Thank you

David

[holmesuser01]

I had a friend with a similar problem. Turns out that there was voltage on his cable line. This killed a freshly repaired VCR that I had just given him. Something to think about.

Hope it's not a big deal to get it working right again.

[Geoff Bourquin]

I just read through this thread and did not see mention of the horizontal drive transformer. Bad connections there can cause intermittents than can drive a guy nuts. A common cause of horizontal output transistor failure. The set can run just fine for hours or days then POOF! I got to the point where every set I opened up got that transformer resoldered.