Riddled TV Repair Forum
Service Menu and Manual Schematics
 
   
 FAQFAQ   SearchSearch   RegisterRegister 
   Log inLog in 
Toshiba CF2768B vert size   Goto page 1, 2, 3, 4  Next  
Post new topic   Reply to topic    Riddled TV Repair Forum Index -> TV Repair
 
Author Message
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Thu Dec 16, 2010 5:14 pm    Post subject: Toshiba CF2768B vert size Reply with quote

Trying to fix an old Toshiba. Model #CF2768B - Chassis #TAC9200
Manufactured May 1992
The picture is 2 inches tall, right in the middle of the tube. Color, sound,
and other functions OK. Don't have a schematic but I see VERT on the front of the PCB next to an IC mounted to a heatsink labeled IC301.
Is this the place to start? If so how to check it short of gambling on replacement? The solder joints looked good, but I resoldered them anyway - no difference.
Google

PostPost subject: Advertisement

JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Thu Dec 16, 2010 6:49 pm    Post subject: Reply with quote

Most likely culprit: C308
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Thu Dec 16, 2010 7:41 pm    Post subject: Reply with quote

Swapped out C308 (220mf @ 35v) - no change.
JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Thu Dec 16, 2010 9:17 pm    Post subject: Reply with quote

Sams # 3194
Less likely C305, C306 and C311 ... a crack in a foil is also a possibility
VCC pin #1 = 12 volts ... pin #8 = 27 volts
Otherwise IC301 LA7837
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Thu Dec 16, 2010 11:21 pm    Post subject: Reply with quote

Haven't checked the caps yet. Voltages check 12 vdc @ #1 and 29.2 vdc @ #8.
Google

PostPost subject: Advertisement

sdtv



Joined: 31 Mar 2008
Posts: 12

PostPosted: Fri Dec 17, 2010 10:40 am    Post subject: Reply with quote

Sounds like a bad cap or caps.

We used to change the red ones ? There was 2 of them one by the big chip and the other closer to the vertical chip.

Those caps with the red plastic cover, the only 2 on the board. (it's a Toshiba thing)

An old trick is to jump the caps from the bottom of the board while the tv is on with a 10uf at 200v or so cap and see if the picture changes.

Discharge it before you try it on the next cap.

If you see a big change then that is most likely the bad cap.
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Fri Dec 17, 2010 2:06 pm    Post subject: Reply with quote

What type of caps do I use? Mylar? Monolithic?
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Fri Dec 17, 2010 3:56 pm    Post subject: Reply with quote

This thing is going downhill fast. I replaced C305, C306, and C311 - no change. Found out my local electronics shop sells the NTE replacement for IC301 for only 4 bucks. Replaced it and no change. After seeing the idea to jumper the caps I went back to the TV and now it won't even power up .
Thats all I get is a relay clicking closed and then open?????? Starting to wonder if it's time to take it to the curb!
JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Fri Dec 17, 2010 5:25 pm    Post subject: Reply with quote

Presuming you're following standard practices when working on the set, the worst that should happen is "no change" in the symptom.

ALL the caps I've mentioned are "electrolytics."

Capacitors being paralleled (if both are within spec and both are the same value) will double the capacitance. If the one in the circuit is open, (and that one capacitor is ALL that is bad) the picture will magically return.

Red Caps C301 & C305 (sometimes 1ufd 50V, sometimes 2.2ufd 50V) I don't believe are used in this set.

Start by seeing if you've blown any fuse and if RAW and STANDBY voltages are present.
1968RT



Joined: 13 Mar 2010
Posts: 51
Location: michigan

PostPosted: Fri Dec 17, 2010 6:41 pm    Post subject: Reply with quote

To JTS1957 - I know all the caps you mentioned are eloctrolytics - I was asking SDTV what type of cap to use for his jumper test. There are 2 large caps as he described, where he described on the PCB. They are brown in color and not polarized. They are labeled C440 (marked 752h, 1.25khp) and C445 (marked 124j, 200). I am a novice at TV repair but not at electronics, so while I understand how various components function and how to test them, I have no knowledge of standard television repair
standards. Thanks for your patience and for sharing your expertise.
Display posts from previous:   
Post new topic   Reply to topic    Riddled TV Repair Forum Index -> TV Repair All times are GMT - 6 Hours
Goto page 1, 2, 3, 4  Next
Page 1 of 4

 


Disclaimer: All information provided by RiddledTV is strictly for information purposes only. Please observe all warnings displayed on your electronic
devices. This information should only be used to help diagnose work, and all service should be performed by a qualified technician.
Contact Us       Privacy Policy       Copyright © 2015 RiddledTV.com       Advertise on RiddedTV.com