wei-ya and makvision

[lilshawn]

I have a tube that was originally from a Makvision 2427. It's missing it's chassis. not sure where it went.

I have a (says working) "Wei-Ya made for Makvision" chassis with the number "C2720C1" I'm wondering if anybody know if this would work. I can't find a lick of info about this chassis from either Makvision or Wei-ya.

my only other option for this unit is a pentranic chassis from a 33" that would need some modding and fixing to get working.

[Rickn]

If the Pentranic is a switchable CH288 use it. Not much needed to be done.
If you have any issues with with or height let me know and I can tell you what to do with it.
Rick

[lilshawn]

thanks Rick, i decided to go with the pentranic and give it a try. it is the CH288 chassis.

but it's got no vertical deflection. (solid horizontal line.)

[Rickn]

You probably already know this but check the vertical output and the integrity of the solder joints C318 can also be a pain (small tantalum). Also Check R336, D401, D399.

Good Luck
Rick

[lilshawn]

Thanks for all your help with this Rick,

as a side note, i did find a 27" chassis so I have been using that not the aforementioned 33"

I found a bad solder joint on R336 so I fixed that up...and the diode next to it was a little loose so i fixed up the solder there.

now there is nothing at all.  screen is black. (tube doesn't flashover white when power is pulled either.) Still got B+ (110 volts DC) and the tube is getting charged with high voltage (arcs when belly button is grounded.) Tube heater is coming on.

I dunno if something else has gone on this chassis or what.

[grantspain]

seen faulty lm1203 ic cause similar issues before-ht present,tube heaters but no picture

[Rickn]

Yes sometimes an LM1203, but it is a highly used IC first look it up on the WEB and chck the VCC pin (I am not at the shop or I would tell you) next measure the voltage and check the dropping resistor in line with the VCC line.

[lilshawn]

I went ahead and swapped the neck boards with another one and I have a picture. Dunno what happened to the original.

So now it's squashed and dim...a bit of foldover on the top.

I fixed a cap that was installed backwards (blowed up C398 after running for about 10 minutes.)

so note to everyone... the white marked half of the cap markings is the POSITIVE not negative like normally encountered.

it looks like this chassis was in the midst of being repaired and then abandoned for some reason.

picture is still dim and folded over...but not blowing up anymore. 

I measured the B+ and i'm at 109. The only info I could find on the B+ was someone who was having problems (went unresolved) and his was at 122.

any info on what the b+ is to be at? I don't want to start cranking on it willy nilly.

[ed12]

simple point here
bad yoke!!!! the wg's are showing it now
chk your impendance on both vert and horz winding's
27"/29" to 33" differ by enough to cause the :exact: problem
u are having
lived it

ed

[lilshawn]

27"/29" to 33" differ by enough to cause the :exact: problem

i decided not to use the 33" chassis...I found a 27" version of the Pentranic CH-288 chassis...and this is the one I have been using.

[Rickn]

Please check the value of R369, it is the heater dropping resistor. Udealy if you have a true RMS meter I would suggest you check the voltage, should be around 6.15. Assuming you may not have a true RMS meter let me know 2 things... value of R369 as well as the make and part number of the tube. For example A68aeg... nade by RCA / Thompson. I may have on file the value you should use for R369??

Rick

[lilshawn]

Yes my Fluke 87 is an RMS meter.

Heater voltage is a little low - 5.85 volts

R369 is a 5 watt 5.6 ohm - reads 5.8 ohms cold

Tube is a "Penaly" P68PTIB82X05 near as I can tell the monitor tube used to be a Makvision 2427.

[Rickn]

Great that you have an RMS meter..
So getting to the issue, Penaly, was a spin off competition of Pentranic. Both but B grade tubes, tested them and relabeled them according to agreed on specs of their customer.
I do not know that particular tube, but my guess it is really an RCA/Thompson tube (In this case the back of the tube will be red in color with grey graphite). No matter try shorting R369  (but do not leave it that way) does the brightness improve??

If so try various values of R369, I am thinking 3.3 ohm, but measure the heater voltage again, try to keep it below 6.3 volts.

[ed12]

hi rick
thk's for helping the nick out

i do however have a question
if the vert is still over/under-scanning
was the yoke chk-ed??
as u an i both know from the wg's this will cause a lot of problem's
ie width,height,b+-loading
ch288 is a smp right?,fet driven,15/25khz on board switchable

ed

[lilshawn]

hi rick
thk's for helping the nick out

i do however have a question
if the vert is still over/under-scanning
was the yoke chk-ed??
as u an i both know from the wg's this will cause a lot of problem's
ie width,height,b+-loading
ch288 is a smp right?,fet driven,15/25khz on board switchable

ed

The yoke seems good. The chassis looks to have had most of the electrolytic caps replaced on it (we mark them so we know which ones have been done)

the chassis is an SMPS supplied board. and it is 15/25 (set to 25)

the orginal makvision 2427 chassis that this tube is from used the same CH-288 chassis

Great that you have an RMS meter..
So getting to the issue, Penaly, was a spin off competition of Pentranic. Both but B grade tubes, tested them and relabeled them according to agreed on specs of their customer.
I do not know that particular tube, but my guess it is really an RCA/Thompson tube (In this case the back of the tube will be red in color with grey graphite). No matter try shorting R369  (but do not leave it that way) does the brightness improve??

If so try various values of R369, I am thinking 3.3 ohm, but measure the heater voltage again, try to keep it below 6.3 volts.

odd... when i jump the resistor the heater voltage jumps to 7.5 volts but the picture isn't any brighter.

just for S&G, I hooked up the tube tester and the emissions are good. maybe this neckboard is no good either.

[ed12]

hi
lilshawn
do me a fav
scope the vert output ic
with the vert side of the yoke hooked up and then un-hooked
vert side olny,and see if the wave fourm change's
if it dose,loaded or un-loaded
then u know the problem
i am just speaking from exp..
also there is a coupler cap alot of ppl take it for a straight electrolic
where it is to be bipolar
4.7/50

ed

[lilshawn]

hi
lilshawn
do me a fav
scope the vert output ic
with the vert side of the yoke hooked up and then un-hooked
vert side olny,and see if the wave fourm change's
if it dose,loaded or un-loaded
then u know the problem
i am just speaking from exp..
also there is a coupler cap alot of ppl take it for a straight electrolic
where it is to be bipolar
4.7/50

ed

ill have to dig out the o'scope and see.

the cap is indeed bipolar




I have a working 25" chassis, if I get desperate, I could pull that one and convert it to a 27" chassis

[ed12]

hi
ok post back to me
as i know rick is busy
and i have most of the mod stuff written down

ed

[lilshawn]

I went ahead and converted the 25" to 27"

changed:

R336 from a jumper to 1ohm

R369 from 5.6 to a 2.7 ohm (actually i went to 2.4 to up it slightly the heater voltage is 6.5 volts so i may go a little bigger to bring it down a bit... 3.3 like rick mentioned is probably going to be about right.)

R724 from 18 to 33 ohm

supposed to insert a 3.3 Megaohm at R768, but none of the chassis or neckboards i have here used it (all empty)...probably phased out. left open.

C908a polypropylene "474" to a  polypropylene "394"

c498 polypropylene "152" to a polypropylene "222"


fired up and looks good. Pic is nice and bright and square. I'm not going to give up quite yet with this other chassis though.

[ed12]

ya
them are change's

I went ahead and converted the 25" to 27"

changed:

R336 from a jumper to 1ohm

R369 from 5.6 to a 2.7 ohm (actually i went to 2.4 to up it slightly the heater voltage is 6.5 volts so i may go a little bigger to bring it down a bit... 3.3 like rick mentioned is probably going to be about right.)

R724 from 18 to 33 ohm

supposed to insert a 3.3 Megaohm at R768, but none of the chassis or neckboards i have here used it (all empty)...probably phased out. left open.

C908a polypropylene "474" to a  polypropylene "394"

c498 polypropylene "152" to a polypropylene "222"


fired up and looks good. Pic is nice and bright and square. I'm not going to give up quite yet with this other chassis though.

yoke is now out of q...
what rick was saying is the heater's tend to draw to much :current: after heating up
what i was pointing at in respect to the yoke
is they fire up great then do strange thing's
worked it out with rick
glad u got her going

ed

[lilshawn]

ya
them are change's
yoke is now out of q...
what rick was saying is the heater's tend to draw to much :current: after heating up
what i was pointing at in respect to the yoke
is they fire up great then do strange thing's
worked it out with rick
glad u got her going

ed

different tubes have different heaters. even though this is a 27, it's heater might be a little bigger and requite a little more current to keep it up at 6.3 volts. if the heater draws too much then the voltage goes low and the output suffers. too high and the guns burn out quicker. I'll have to change the resistor (R369) to get the voltage to about 6.3 volts. not a big deal.

The B+ on this good chassis is about 106 volts, it's lower than the goofy one (109 volts)

curiouser and curiouser.

[Rickn]

Sorry guys, I do not always check the forum, so pls feel free to e-mail me direct rick@niemandisplays.com.
Sort of lost track of this but when you shorted R369, the picture should have gotten brighter, do not leave it that way. The B+ should be around 115volts on the 27inch tube. Width will shrink and vertical size will increase.
Might help the foldover!
Back to the picture, please set all of the controls on the neck board to mecanical center, the drive controls could be set to 2/3 to achieve a better brighness. There is a control marked sub-brightness on the neck board as well, this should also be set to mechanical center.
Now reduce the user contrast control to minimum, brightness to max. If you have a generator and can switch RGB off that helps. Next step adjust the G2/screen control so the background raster is just black, turn the colors back and increase the contrast, If the the picture is now good (with exception to size and foldover) we can move to the next step.
If still dull we will move to the "cheat" which repeats all of the above, but reduce the setting of the sub bright control (feeling in from the back of the neck board it would be clock wise and the brightness will reduce). This will allow a higher G2/screen control setting.

Rick

[ed12]

hi
ya rick thk's
he is now talking about the b+..rem we went over this goffey problem once with 1 of mine?

lilshawn
vr501 on the smp moudle should raise/lower the b+
if not there is a cap mod,short of that we are going back to loading
106/109 is far to low
u are pulling current some where
the flyback # is ?
this will tell me more of the trick to the tail

ed

[lilshawn]

thanks guys
see that's the thing
the good chassis is measuring 106 and it looks great.
the bad one is 109 and looks terrible
Mind you i'm measuring it on the output side of D501
just before the choke L501.
there would be a little bit of noise but not a big deal
it was just easiest to get it there
I could be different after the choke coil i could try there.
i'll hit it again tomorrow.

[ed12]

hi
yup that is the proper spot to chk reg output

mod is c511 slow start cap

mind u your yoke is still in q here

my note here refer to .65-.8 mh
horz

c908=width

thk rick for that 1

ed