avcom psa 35

[budm]

Re: avcom psa 35

You need to use DMM to check the leakage resistance of that cap, it should show open circuit, we are not checking for ESR.

[electro1]

Re: avcom psa 35

output and ground of 7915 meter set at 2000k I get 322 set at 200k I get 1880 and climbing once its hot its at 1995turned off let it cool a little then back on and at 2000k its 337 and at 200k meter shows oL then after it cooled down I turned on and measured the 7915 and the probe slipped momentary between the input and grnd or output pins now there is no horiz line on the screen the 2000k i got 322ohms before probe slipped the 7915 is very hot so its probably shot now. removed 7915 first it said faulty now it saying led or diode junction before the probe slipped the forward voltage was 2.80v and test current is 2.34ma it said diode junction not sure if it said led also now it says led or diode junction and forward voltage is 2.76 and test current 2.38ma
tested 5 x same reading. That red cap has printed 220k on it
and z75 under 220k

[budm]

Re: avcom psa 35

That red cap is 220pF 10% Z5U type, so does it have any leakage resistance on this cap?
"removed 7915 first it said faulty now it saying led or diode junction before the probe slipped the forward voltage was 2.80v and test current is 2.34ma it said diode junction not sure if it said led also now it says led or diode junction and forward voltage is 2.76 and test current 2.38ma"
What is the 'IT'? I.E. "it said" and where is this 2.38ma from?

[electro1]

Re: avcom psa 35

That red cap is 220pF 10% Z5U type, so does it have any leakage resistance on this cap?
"removed 7915 first it said faulty now it saying led or diode junction before the probe slipped the forward voltage was 2.80v and test current is 2.34ma it said diode junction not sure if it said led also now it says led or diode junction and forward voltage is 2.76 and test current 2.38ma"
What is the 'IT'? I.E. "it said" and where is this 2.38ma from?

those readings are from a componet analyzer a peak dc a55
the z5u cap is reading capacitance value of 230 pf

[budm]

Re: avcom psa 35

I do not think your analyzer will be able to test the regulator since it is an integrated circuits with many semiconductors inside, best bet is to replace the 7915. That red cap cane be left out off the circuits, the circuits will still function without it, we're just trying to find out if the cap is bad since cap does not get hot unless it is shorted out and acts like a resistor instead, but come to think about it since it is mounted so close to the Diode, may be that is why it gets hot because of the Diode.

[electro1]

Re: avcom psa 35

the tester said diode is good cause it did not come up as a short are you thinking that the resistor is getting hot cause its close to the diode or could the diode be bad if so i will get a diode. Looking at the board I see the icm7555 ic is inline with that 7915 maybe the 7555 chip got shorted when the transistor was shorted if so can i use any 555 ic there is a cmos version a tlc version does it matter which I use. I put the cap not as close to the diode as it was i made a soder bridge on on the right sides i will have to raise the left side to with solder picture will show the right side is higher up Im going to replace the 7915 and leave the cap out of the circuit

[budm]

Re: avcom psa 35

Yes leave that cap that is soldered in parallel with that Diode for now, not sure the CMOS version of the timer 555 will work or not, I believe it should.

[electro1]

Re: avcom psa 35

Update I just got the voltage regulator time permitting I will be installing it.

[electro1]

Re: avcom psa 35

correction its a cm7555 timer on the flyback board what is it for? . Here is the sweep board picture. There is a blue band then yellow band then black with a white dot 2 pin componet on rt side bottom of picture any idea what this is its at the bottom of the picture just above white Potentiometer. That input is still 28.4volts on regulator 7915 on flyback also with the sweep board disconnected that resistor on top of diode is cool to the touch.can it still be shorted. It only gets hot when sweep board is connected.

[budm]

Re: avcom psa 35

The 555 is a pulse generator for blanking the screen during beam return for the next scan cycle.
Are you talking about the red cap ("that resistor on top of diode" that is solder across the diode as shown on post 26, you can lift one leg of the red cap and it still should work.

[electro1]

Re: avcom psa 35

Yes the resistor on top of the diode in post 26 ok im gonna unsolder one side of that resistor there are 4 red tantumson sweep board im checking to see if any of em are shorted. The 4 diodes are all reading 0.61v -0.62v forward voltage and 4.60ma test voltage. With my mutimeter its reading 0.61-0.62 one way only so they seem good to me. There is a colored sandwich green vilot black 2 lead componet it has a white dot on it and attached is a picture its at the bottom rt side next to white Potentiometer what is this and how do you figure out if its good.

[electro1]

Re: avcom psa 35

I tested one of those red components has 2 leads its mounted vertically says 4.7 + 35 also has a long white stripe going up vertically is this a capacitor or resistor the part is on top of the ic to see it better I tested it showed infinity on meter tested again 000 on meter that tells me it's shorted also is that big green retangle on the right side a capacitor or resistor ? thank you

[budm]

Re: avcom psa 35

That is Tantulum cap 4.7 uf 35V, I hate using them because the fail mode is shorts (when they go bad, they shorted out, same for CERAMIC cap). I would replace them with low ESR cap such as PANASONIC FM/FR series. Please note that these stripe ont the body can be POSITVE or NEGATIVE (I learn that the hard way) depend on manufacturer. Check the votage polarity on the pads where the cap goes into and mark the board with a marking pen. look real close at the body and see if you can see + printed on the body.
I see that you have more than one of these TANTALUM caps. I see 3 of them. I think you have found the cause of the problem.
The big green component ia Polyester film cap.
The component with color stripe with white dot looks like a cap, not sure but need to see how it is hooked up and if it is on the schematic. It looks like one leg is attached to Ground and anothe leg is attached to pin 1 or pin 2 of the left IC a shown in post29.
I f you look at the circuit on post15, you will see C2, C4, C6 labeled as 4.7T 35V, The T is for TANTALUM. C5 looks like the mylar cap attached to the IC U3 PIN3, verify.

[electro1]

Re: avcom psa 35

I looked at the schematic u4 pin 3 looks like its going to the polyester .47k 250v is this correct 47k means 47,000 and 250v means voltage rating ? Cap on schematic U3 is the mylar cap to pin 3 also cap lead on pin 3 is bigger. When replacing you said use the flr series electroytic cap and not to use the tantlum. I did mark the board where the white stripe is, these 4.7 tantlum are they pico, uf, nf at 35v? On the flyback board that 220pf z5 cap soldered on top of diode is connected via circuit trace pin 2 of the 7915 so its shorting out causing the input voltage on 7915 too be at 28.4v is this correct. On another board in this unit there is 1 blue Tantulum and 1 red Tantulum negative side twisted together going to rf block and + side going to circuit board. I did put the meter on those without untwisting them it shows infinity can you test em twisted together that way?

[budm]

Re: avcom psa 35

"C2, C4, C6 labeled as 4.7T 35V" They are 4.7uF 35V Tantalum as you can see in the diagram. Replace them with low ESR FM or FR series by Panasonic. Look real close to see which leg is positive and which leg is negative on the original TANTALUM caps. Like I said before " Please note that these stripe ont the body can be POSITVE or NEGATIVE (I learn that the hard way) depend on manufacturer."
That white stripe can be POSITIVE or CAN BE NEGATIVE, so look at the cap and see which leg is connected to the circuit ground as shown in the diagram. MAKE SURE YOU FIND OUT WHICH PIN IS WHAT.

47K 250V = 47000 nano farad = 0.47uF 250V

That red CEARMIC cap that is soldered to the top of the Diode that you said is getting hot, if it does get hot then it is shorted out, that cap should never get hot, it does not have enough current to flow through it to get hot unless it is shorted out, like I said, you can leave one leg disconnected for now.
They negative leg may be sharing same ground point, it looks OK since it does not show shorted circuits.

[electro1]

Re: avcom psa 35

The ceramic resistor the one on the diode on the flyback board 220pf z5u what is the voltage rating? Before I removed that tantlum I tested it with the esr tester it said .24 ohms in circuit after I removed it from the circuit it still read in circuit .24 ohms I thought at first the tester killed the 4.7 uf cap or the circuit was affecting reading cause it read 4.2 on multimeter and i did not know if it was a resistor or cap now I know it probably was on its way out the 4.7 tantlum has a + on the right most pin. The other 4.7 cap is reading 5.0 on 200 resistance setting.

[budm]

Re: avcom psa 35

That is not resistor as I had indicated many times, it is 220pf capacitor (100V should be fine) for Diode noise snubber, again you can leave this cap out for now.
TANTALUM cap will fail in shorts circuit mode, that is why I suggested to replace them, unless you will want to wait until more of them shorted out and take out the power supply circuits, it is up to you.

[electro1]

Re: avcom psa 35

I have some 4.7uf capacitors here at 50v is that ok to use?

[budm]

Re: avcom psa 35

You can use that for now for testing.

[electro1]

Re: avcom psa 35

220pf z5u capacitor can it be 50v or does it have to be 100v can I go up in voltage say 500v 1kv, 3kv whats a good temp rating.