k4900 vert. collaspe

paul400

Well-known member
Joined
Nov 8, 2010
Messages
2,416
Reaction score
219
Location
Hixson, Tennessee
messing around with this chassis, checked Q302 and Q303 just replaced anyway, checked resistor r313, within spec.recapped chassis. checked continuty on the yoke wires to all their points. replaced IC. 301. checked all the resistors and diodes in vertical section in circuit, had a working 4900 to compare. ohmed out all vertical pots in circuit and seem to be ok. TP82 is giving me 55vdc . on my working chassis I am getting 32vdc at tp82. also the heat sinks on Q302 and Q303 the pads that are anchoring them down are completely burned off but dont seem to be electronicly connected to anything. any suggestions?
 

Attachments

  • 100_1810.jpg
    100_1810.jpg
    28.6 KB · Views: 28
Paul look around the back edge of the board, you'll see two jumpers that look like staples. Make sure those are connected well, check the continuity between them.
 
checked those jumpers and reflowed but no dice. still collasped, quess I will go have a turkey sandwich till I think of what else to do.
 
The back corner behind the flyback is well known for solder issues or cracks. And that happens to be the vertical section...
 
1. replaced all the vertical pots
2.ic chip
3. vertical transistors
4. tested all the resistors and diodes in vertical section
5.checked yoke connections and all points to.
6. full cap job
7.reflowed all solder joints
8. continuty check on all vertical circuits " from solder joint to solder joint"
I must be missing something so simple!!!!!!!!!!!!!!!
 
I have vertical deflection. went over the board one more time and started reflowing some stuff I already went over and discovered R304 was missing. put a new one in and works again. went round and round to get to this resistor.
 
Back
Top Bottom