[TechAssist] Re: citizen model JCTV2704 chassis M3L523S
- From: "Damon" <damon101@xxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Wed, 4 Aug 2004 22:50:35 -0500
Ooops, when you stated base waveform, I thought you meant base as in
"baseline".....( I rarely check base waveforms), normally they look like a
"raggy" square wave anyways.....
However the collector waveform should be a smooth pulse, about 12uS wide,
anywhere from 1000V to 1100V max on most TVs, probably 80% ride right around
1050V.
The caps can induce a raggy looking collector pulse or heat up a transistor
pretty fast if it's nearly open.....partly open/low value can cause it to
fail like yours is. That 12uS pulse width can point to the problem
too......more than 12us generally indicates bad IHVT/leaky cap (lowered
voltage too), less than 11uS would show opening caps.....so the 12uS check
is another tool in our toolbox...
Damon Brunger
Telrad Electronic Services
Ft Wayne, IN 46815
----- Original Message -----
From: "Alvin Rose" <ajroseca@xxxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, August 04, 2004 9:18 PM
Subject: [TechAssist] Re: citizen model JCTV2704 chassis M3L523S
| Hi Damon
| I will check the capacitors in the collector circuit
| and the divider ladder in the pincusion circuit..the waveform
| I referred to was on the output transistor Base lead
| would this effect the input to the base lead.
| Alvin
|
| Damon wrote:
|
| >You have open or off-value high voltage caps on the collector, you may
also
| >find bad caps in the pincushion's "divider ladder" . The spikes and
"square
| >wave" effect are the indicators.
| >
| >Damon Brunger
| >Telrad Electronic Services
| >Ft Wayne, IN 46815
| >----- Original Message -----
| >From: "Alvin Rose" <ajroseca@xxxxxxxxxxxxxxx>
| >To: <techassist@xxxxxxxxxxxxx>
| >Sent: Monday, August 02, 2004 9:40 PM
| >Subject: [TechAssist] citizen model JCTV2704 chassis M3L523S
| >
| >
| >| Hi Guys
| >| we have a citizen tv which is shorting the horrizontal output
| >| transistor..Have replaced it twice..Set will run for half an hour
| >| and then will short the transistor..Scoped the collector and there is
no
| >| saddle in the waveform but a small amount of ringing on the reference
| >line.
| >| The base waveform looks like a modified square wave with a number of
| >| high spikes at the start and finish of the waveform..I replaced the 22
mfd
| >| electrolytic in the primary of the driver transformer with no
improvement.
| >| Driver transister tests ok..Had anyone had this problem with this model
| >| Your help is appreciated
| >| Alvin Rose
| >| Radio & Tv Centre
| >| Marystown, Nl
| >|
| >|
| >|
| >|
|
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