65 maggie
 

hi all, i am certainly not looking to run up another thread like the last one, but this 65 maggie roundie had a new crt in it but i since traded with another set but the problem i have is the screen is very dark with the new crt and the one i put in. the bias is a switch and if in the min position no screen at all if in the middle i can start to see the screen bearly but with the switch up i have a screen but its very dark. the thing here is the crt thats in it now seems to have a problem with the green gun heater not heating up sometimes and if i tap the neck the blue sparks happen and then its good but i would like to maybe correct whats happening with the lack of brightness and can only get just that with the bias maxed out. i changed the boost diode that was bad, and checked all the high wattage resistors. the voltage at the hot is around 172 volts i dont think it should be that high but then again i dont have a schematic that gives voltages. i was told the chassis was a 16 clone by moyers as i had bought a new fly for a spare and it is correct for the chassis but the rca schematic dont show voltages. maybe this is a simple fix, dont know but at least the chassis will be ok if the crt takes a final dump and if i come across another crt then ill be all set to go. the crt now does work but how long the heater will last i dont know. i feel bad asking for any help since the last thread, lol,lol im sure everyone wants me to fade away, lol...; :smoke:

check HV should be 23-25kv, check focus voltage should be 4-5kv
check crt voltages should be about 280v on the cathodes, 180v on the G1 and 700v on the G2. From there you know where to look.

hv is up where it should be so ill check those crt voltages. "from there i know where to look" lol,lol ok ill see what i can confuse myself with,lol lol... thanks dave.

Timmy, PM me with you email and Ill scan a schematic for you. Does the mag chassis sticker say its a U43 or U45?
I have the Tab Magnavox Color TV service manual by Stan Prentiss, and it helped alot on the 64-70 Mags I ve seen over the years.
I recall having issues in the Video amp stage.

ok ill get the back off and see what it says, this is a combo so ill have like 25 screws,lol. :yes:

ok all there is on the chassis is 10- 65 g date, and stamped in black ink is , 5 45 5 thats it unless there was more to the tag but its gone. and the model says on the cabinet 20t567k

If it has automatic degausing it will be a 45 series chassis. Thats whats in my 65 combo.

yes it has auto degausing and instant on but i dont use that.

well im not sure if the problem here is in the blanker circuit but the g1 is 159v bright up and bias ccw. otherwise the voltages are close depending where the rgb drives are. but i cant set it up unless the bias is maxed, thats not right, so im looking...

thats a bit on the low side, but you need to find out what the cathodes are, those are directly coupled to the video out tube. You want approx 100v difference in the cathodes to G1 voltage (cathode should be higher).
the greater the difference the more cut off the tube will be (darker). It does not take a lot of change to go from dark to bright.

well it turns out that the g1 159 v is the red the others are 165v the g2 900-1000v and the cathodes 305-318v

well there is the problem cut off due to bias of CRT well over 100v

i tested these with the crt cap off because its difficult to test with it on , hope it dont matter. and this was again bright up bias ccw.

I would start by trying a new video out to see if you can drop the cathodes down. if a known good tube does not help then you are back to checking voltages.

The g1 seem a little low as well. so checking the difference amps voltages would be in order, does the CRT bias have any effect?

the crt bias does raise the voltages on the g1.

is this a U45 or an RCA clone?

U45 crt bias pot adjusts the G1 where the RCA adjust the cathodes.

the only way to get a picture or anything on the screen is with the bias maxed and still dark. bias ccw nothing on screen..

in that case I would try a new video out tube for starters.

i dont know if its the 45, 5 -45 -5 is stamped on the chassis its a gold color chassis if thats any give away.

it may be a clone because the rca 16 and 16x chassis uses a 12by7 but this one uses 12gn7

if that does not help trace from the bias pot to a 220 resistor and a .22 cap. the resistor should be isolated so you should be able to check in circuit. You will need to lift a leg of the cap and test with an old school cap tester for leakage.

Its not a clone if the bias pot wiring is as described (bias adj the cathodes of the diff amps, thereby the G1's) close but not a clone

oh and check the 27k power resistors in the plate circuit of the diff amps, should have 410v on one side.

g1 , solid colors the bias adjusts the voltage. and the bias pot is mounted on a board and there are resistors on that board and i checked all of them so it may be under the chassis, wish i had a schematic...

just look for a 220 resistor off the bias pot.

look for a 3.3 meg resistor that goes to one side of the user brightness control

there is one 27k high watt resistor 405 one one side and 244 on the other, and tests perfect. that 220, ohm or k.

the 220 ohm resistor on one end of the bias pot is fine. the .22 cap near the diff amps checks lower in capacitance then another good one i have but its good. it will be very difficlut to reach the bright pot to see if it has a resistor on it. well there is no resistor on the bright pot and without a schematic it will take for ever to find because this thing is a combo and all controls are on one side and has long wires with no plugs to detach from the chassis, omg...

lets stick with this for a bit, the 244 should be fed thru a 100k ohm to the G1, and should not be dropping to the 160ish you mentioned before, find the 100k resistors that have one end on the G1 and the other to the 405. Something not right, the 244 should be at G1 as well, there should not be any loss across the 100k resistors in the G1 circuit.

looking from the rear of the set
chroma board
left side
back of board
look between the tube in the corner and a exposed coil for the resistor.

ok there was 3- 27k resistors and they are all ok and there is a 100k resistor at each g1 wire and they too are good. and also one other 100k also good.

ok what is the voltages on both sides of the 100k?

my last post i said there was an additional 100k but it was a 180k, also good. there are no other 100k resistors on the chroma board except each one at the g1 wires.

the 180k has 405 one side and 179 on the other if this matters. if i let it warm it goes to 185 v

I am trying to figure out the G1 voltage, IIRC you had about 160v, but if the 100k resistors have 185 then it should be 185v, which is in the normal range for the G1. Note this is highly dependent on the CRT bias so maybe you adjusted it at some point and got the differing voltage being reported now.

this voltage is from the 180k that i thought was another 100k, was my mistake but the voltages on the g1 are 100v probably because i have the chassis hanging out of the cabinet. but still they are low and this 100v is at each 100k resistor , g1.

ok lets start over again

CRT
G1 voltages
cathode voltages

ok im going to do this with no yoke or crt plugged in, is this ok ?

ok with these things no plugged the cathodes are 340v and the g1 99v i guess lower from befor because the crt and yoke are not plugged and the bias is still ccw.

well you should test them with everthing installed, that being said those voltages are wack.
the 99v does not make since, if the 100k resistors have 180 one the low side, then the G1 should be the same.

no the 100k resistors dont have 180v the single 180k resistor i mentioned has that on one side.