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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Magavox PTV705 blows HOT instantly
Bad flyback, cracked blue crt (very common), bad hv divider, etc.
Just use standard tv set high voltage circuit troubleshooting techniques. David wrote in message ... Hi. Magnavox PTV705, blows Q802 HOT instantly. Have checked, good H drive to base from proc chip, with HOT removed and HV cable detached to avoid crt problems. Anyway, done up with HOT removed and HV isolated, I can fire up for 1 second. During this time I have good base signal to HOT base connector. If I put in new transistor, makes a not pretty noise, then is instantly shorted. Have found no obvious bad parts near the area. Any ideas? Thanks in advance, Danny |
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Magavox PTV705 blows HOT instantly
Hi. Magnavox PTV705, blows Q802 HOT instantly. Have checked, good H drive to
base from proc chip, with HOT removed and HV cable detached to avoid crt problems. Anyway, done up with HOT removed and HV isolated, I can fire up for 1 second. During this time I have good base signal to HOT base connector. If I put in new transistor, makes a not pretty noise, then is instantly shorted. Have found no obvious bad parts near the area. Any ideas? Thanks in advance, Danny |
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Magavox PTV705 blows HOT instantly
That Q802 is the Horizontal Output Transistor.
The High voltage is done with Q906, the HVOT. These sets suffered from lack of sealant for the anode connectors to the CRT's causing your exact symptoms. Good Luck, Bill Jr wrote in message ... Hi. Magnavox PTV705, blows Q802 HOT instantly. Have checked, good H drive to base from proc chip, with HOT removed and HV cable detached to avoid crt problems. Anyway, done up with HOT removed and HV isolated, I can fire up for 1 second. During this time I have good base signal to HOT base connector. If I put in new transistor, makes a not pretty noise, then is instantly shorted. Have found no obvious bad parts near the area. Any ideas? Thanks in advance, Danny |
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Magavox PTV705 blows HOT instantly
Hi. Thanks for the ideas. It does blow the Q802 with HV cable removed from
splitter and isolated also. Reckon this set doesn't like having no load on HV output? First time I've run into this, so a bit of a learning curve. I gotta change the tube oil anyway, it is grungy, so I'll redo the RTV at HV connectors while I'm at it. Just trying to sort out the running problem first before the cosmetics. Cheers, Danny |
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Magavox PTV705 blows HOT instantly
On Thu, 11 Dec 2003 23:00:08 GMT, David Heller wrote:
wrote: Hi. Thanks for the ideas. It does blow the Q802 with HV cable removed from splitter and isolated also. Reckon this set doesn't like having no load on HV output? First time I've run into this, so a bit of a learning curve. I gotta change the tube oil anyway, it is grungy, so I'll redo the RTV at HV connectors while I'm at it. Just trying to sort out the running problem first before the cosmetics. Cheers, Danny Danny I would reflow the horiz drive transformer. You need to do the four pins where the tiny leads from the windings are connected to. and resolder the connections where the transformer is soldered to the board. Other possibilites are a bad yoke or horiz drive problems Also the damper diode could be bad if not internal to the output transistor. Also check for open safety (tuning) caps off the horizontal output. I recall a Philips PTV620 few years ago the would blow the HOT instantly. In that case, the cause was C817 (0.0091uf/1600v) Alan Harriman Dave Good Luck |
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