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PTV300 P/S repair

Just in case anyone else out there has one of these relics still working...

I replaced the white flyback with 45 degree HV output (362003-5) with an HR equivalent for the 362003-7 after looking at the specs for it and the later

362140-1. It looks like pins 1 and 3 were switched between the two styles and the APW007 P/S board that I have had both sets of locations and sure enough, those two pins are swapped. I also had to move one of the resistors to the back of the board since it was physically in the way. Bought five of these transformers on eBay for $32 total...

So... Put a 150watt light bulb in place of the fuse and turned the power on. Slight glow from the bulb and the set turned off. Put in the fuse and turned the set on. Works! One thing that bothers me is that the troubleshooting manual states that there should be > 100k ohms between TP3 and TP7. With a DMM, I get very strange results. Up until I get to the high ohms range, I get infinite and then it drops down and increases. From the schematic, it appears that I'm charging up a capacitor or two. Using the diode test, I get a basic voltage drop in each direction. Would this be different with a VOM? I have a dud board and pulled every diode and transistor in on the B+ circuit. Only by removing the capacitors was I able to get the >100k reading on my DMM.

What other failures can I expect from this chassis series? I've resoldered most of the old square thru-board connectors on the p/s, deflection and convergence boards. Used fresh heatsink compound on the large transistors, replaced the coolant and converged the set.

If the picture weren't so good, I'd replace it...

Thanks for the help...

Kirk S.

Reply to
Kirk S.
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So you got what I needed about 7 years ago. Marvelous.

You know what you got there, a piece of technology that isn't made anymore.

I will splain.

The main 130 volt regulator in that set is the HVOT driver. The regulation can be so tight that the picture shrinks on high brightness due to the mass of the electrons. Therefore they have a secondary regulator. See, in a PTV raster size must stay pretty constant. If not, convergence would never follow. I mean they had a chart for every kilovolt that dropped per milliampere.

The main regulator is synced of course, and as it spreads it's on time to handle the load, and HV is increased pre-emptively. It is a wonderful system, but a real bitch to work on. They were a bit self-destructive, with 320 VDC on tap it was not hard to go poof.

Amma tellyas one more thing about the early PTV300s, do not work on them in a basement, even WITH an isolation transformer. Just don't do it.

T
Reply to
ZZactly

I got it free about five years ago. Worked pretty good until a "tuning?" capacitor on the deflection board smoked. Worked another couple of years and the old white HV transformer died. Bought a set of boards on eBay and it worked another four months. I have no idea how long my "fix" will last.

Probably for more than one reason... Very few integrated circuits and discrete components that can be tested and replaced with a little know-how...

Magic, eh?

Yeah, not knowing what some of the zener values are doesn't help much either...

I don't trust electricity to follow the rules. As a hobbyist, I unplug the set first, verify that there is no voltage on the test points and THEN use clips to hook the meter up. Place the meter on top of the set, verify the wires are out of the way and then plug it in. The only thing I'm comfortable testing on live are old digital circuits like Arcade games and only then on my test bed; not mounted inside the machine with open line voltage connections.

Like falling off a ladder, you may only get one strike and be out...

Thanks for the info...

Kirk S.

Reply to
Kirk S.

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