84 Magnavox console TV
 

I am still pretty new to working on TVs and this looks like it is going to be a real challenge for me. I just picked up this Magnavox TV from an auction close to my house and I don't no wy I bought it as I don't have any room for it but I digress. The TV was plugged in at the auction so I truned set on and while the tube was warming up the set power cycled off and on and eventually came up to a very bright snowy picture. There also was little bit of blooming on outer side of picture so the CRT is differently got some hours on it but with britness and contrast truned all the way down you can still see raster in the bright light. Wen I got the tv home I took of the back and blow out the dust. After that I took an RF modulator and DVD player hooked it up to the set. powerd that set on and then it powered cycled a couple times( when it power cycles the led display goes off too). Once the CRT warmed up I got a picture that looks like horizontal is not locking and think the vertical was locking as well but I'm not sure as I didn't leave tv on very long. Also I got out of the speaker a loud buzz or some might call it hum adjustable with the volume control. I did not take a picture of it set on as I was afraid of causing more damage to other components. So I quickly truned the set off. The TV did have an old repair shop tage in side it. Saying that the tuner had been worked on in the past. I do know the tuners on these tvs are known for giving trouble.

First post the chassis number & a chassis pix of the set.
Next pull back the chassis & give it good looking over for
hot spots, cold solder joints, bulging caps etc.
You may want to post a short U-tube of the problem. Use
a live show, not cartoons.

73 Zeno:smoke:
LFOD !

Well the tv is kinda working on this power up. I here it ark and the tv truns off and back on. Sometimes when it comes back on it loses sync audio buzzes. After it's on for bit it behaves. As I watched a full length movie and it did not misbehave once. model number is CE4746AK02. I will porbly have to take the back off again to get the chassis model number as I could not find it on the back. The CRT is actually very strong and has a very sharp image. Also has a very loud and clear sound. Sorry about the video not being rotated correctly but I can only get the tv to misbehave when it starts from a cold start. The video still shows the problem. https://youtu.be/ck5eew48ADQ

when I have the time I will pull the back of it and give it a service

Looks good & strong.
To find arc pull back, turn off room lights & fire it up.
If what you hear is external you will see it.

Zeno

I took the back off and gave it a look and on the top side of the board I didn't see anything that looked burnt. I also undid the for screws and lefted the board up then I looked at the bottom of the board for bad soilder joints. I didn't see anything that had any obvious bad soilder joint. When I take the board out of the set I will give it a more indept look over. Finally I put the board back into place turned the lights out so it was pitch black and turned on the set. The set did misbehave but I didn't see any thing at all but this time it only did it once. After that it worked fine. I don't know we're to start as it is intermittent and those problems are the worst to solve. Ok here some pics of the inside and here is the board ( MC2 Main Board 25C5 A10154 NC)

OK its a C-5 chassis. They did get cold joints in the hoz out area
& if left alone they will burn the PCB. There are a few caps going
from the E to C on the hoz output transistor & thats where most
of them went cold.
For the arc you can also use a paper towel tube as a stethoscope
to localize it.

73 Zeno

I took the chassis out and connection look good but I resolder them anyway. Not being confendet that would fixs the set. I started testing components that might give trouble wile the set is cold but get better after being on. Which means I tested the caps and found out that all of the Phillips branded capes were completely bad reading in with very high esr, capacity in NF range, and very high voltage loss. There were ten Phillips capacitors in all and they were all bad. So to anyone how has a tv from this time period it seems those Phillips brand caps are garbage now. I have had to order some replacement caps as i naturally don't have the ones I need. Do to age of the set being close to 40 years old I decided to recap most of the tv as in past I had left some caps that tested good and little whileone of them blow up some expensive parts. I don't often recap stuff unless I feel it needs it.

I fixed a number of those, back in the '90s. Cold solder joints on the horizontal driver transformer, the horizontal output transistor, flyback transformer, and on the HV capacitors are common and they often won't look bad. Sometimes, all it takes is a micro-crack in the solder joint to cause problems. Also, that yellow capacitor on the right- hand side of the board would sometimes arc and burn. I ran into a few bad flyback transformers on these and if yours ever goes, you can probably hang it up because they were NLA 30 years ago.

Well I found the porblem and I'm afraid it might mean the EOL for this tv as the part that is failing is the flyback as after I replaced the bad caps and resolder all of the connections. I truned on the TV to same results but this time I had the back of and listened and I could faniltly here arcing internaly coming from the flyback. when looking at CRT while it was arcing it stayed perfectly fine. Sometimes it would arc very loud and the tv would power cycle as it was doing before. It's a shame as other then that the tv works perfectly and has a fantastic picture and the cabinet is in like new condition. I now flybacks are very fail pron but I like to know why every CRT TV I get being from 70s-2006 when it fails it is always the flyback transformer. I can never get the cheap easy repairs. I will try and get one off a junk tv or a new old stock one. If can't find one the tv will be busted up for parts

The C5 is a super common set so you should be able to find a FBT.
Get the numbers off the old one & from the manual.
BTW any distributors still have NOS NAP parts ??
BTW #2 C-5 was used in Maggy, Sylvania & maybe Philco so check
all 3 brands.

73 Zeno

The flyback is 361969-1 and I think I might have already found a replacement one already. I'm just waiting for them to get back with me.

Well scratch that off as being the flyback and no didn't replace it. I turned the seat on and ran tv for Halloween for playing music videos for over and hour. In that time the seat worked perfectly except when first turned on the TV did the exact the same thing it always dose the TV power cycles maybe once or more times then behaves fine. The tv was in garage will it was raining and very humid. The seat still worked fine and if it was the flyback it porbly would have blown up in short order. Back at square one and I'm afraid I am completely stumped as it is intermittent porblem and I have no clue what could be causing it or were to look.

CRT looks new so worth time.
Try tapping around when the set is NOT acting up & see
if it does it. 90% chance its a cold joint. Trouble is if not
fixed it may burn or blow out a bunch of parts in a
chain reaction.

73 Zeno:smoke:

I did resolder a lot of the connection but I may have missed some. I will go through it again as soon as I'm able to.

Its best to pull the whole chassis & put it on a bench with LOTS
of light.
Also RTVNUT mentioned a yellow cap. If its a square one they are known
to get too hot & bulge. You MUST use the right type cap or it will blow.

Zeno

the tv dose have square yellow cap close to the flyback. I presume it's a film cap it has not failed yet but porbly should be replaced.

I did look at chassis on bench but nothing looks bad on ether the top or bottom of the board nore dose any component look bad physically bad. I also resolder ever solder connection on the board as to element any chances for bad soldier joints. Since nothing changed it most be a bad part.

I did some looking through the same I have and thing I have made some progress.

This info comes right out service manual

Shutdown from an overvoltage or over current condition is preformed in the SMPS. When there is an overvoltage condition in the chassis, a High singal is applied to the base Error Latch transistor, Q494, from the overvoltage sensing circuit. When Q494 is turned On, grounding the 7.1Vdc bus, which removes the source voltage for Q470. an overcurrent condition will will create a negative singal at pin8 of T48, which will forward bias, the overcurrent Sensing Diod D465. This negative signal will be applied to emitter of Q494, turning it on, shutting the chassis down. The chassis will try to start and run again as as error causing the condition goes away. This can produce a sound of "ticking" from the chassis.

That is exactly what my seat is doing when the seat is first powered on after that seat runs fine with no trouble. Know I got find what could be causing the porblem it's eather overcurrent, overvoltage, or the SMPS has a part that is failing. At this time I can't test for high voltage as a currently don't have a high voltage porb.

Here is link to service manual. I will remove it if any has porblem with being posted here https://drive.google.com/file/d/14kw...w?usp=drivesdk

OK this is probably one of the nastiest power supplies ever used
in a TV. Only the Sony double SG613 may be worse.

You need to find if the SD is from a fail in either the TV or SD.
Looking at the pix its near perfect so odds are its a SD problem.
I assume the arcing is the SMPS making the TIC TIC.

BE AWARE this set has 2 major grounds !! You want to use the HOT
ground ( blank triangles ) for voltage measurements.

Anyhows you may want to use freeze mist on it & see if you can knock it out.
Start at Q492 v& 494. Also Z402. Also any 'litics in the area. Just a few parts at a time. If you hit it put freeze on a Q-tip & touch the suspect.

73 Zeno:smoke:
LFOD !

Would this transistor be a good substitute for a NTE159 as dummy here broke a lead off one of the originals when removing to put it in a component tester. Once I get my freeze spray and put a new transistor in I will trune seat on use freeze spray and see if that helps me find the bad part. I have substitute a transistor before and just wanted known if the one I found would work.

KSA916YTA
https://www.mouser.com/datasheet/2/3..._D-1810346.pdf


NTE159
https://www.nteinc.com/specs/100to199/pdf/nte159.pdf

I put in the new transistor to replace the one I broke the lead off of. Truned on the set and it powerd on. I could hear arching and in the past I just thought it was static electricity from first turning on the TV as arching quites after little bit of time. Now I know that is not the case as I paid closer attention. Noticed with volume truned all the way down to element that static as it will over shadow the pops and snaps coming from the speaker. After about a minute it stopped like it normally dose. Still thinking it might be temperature related I tired using freeze spray and that did nothing set still worked as intended.

So I believe now that the protection circuitry is working as intended. Something is arcing and sometimes it arcs bad enough to trigger the protection circuitry to shutdown the set. After a while the arcing gets less server so the set stays on but still arcs a little bit. After a while it quits arching completely and the set will run fine. You can turn the set off and come back to set with in hour and trun the TV on. It will come on and not arc at all.

I do know that arcing is coming from something internally as I have tried looking at the set in pich dark and could not see it arching at all nor do I see any carbon or burn marks were something has been arching. I do know it's coming from the right side of the main board. It could be the flyback but I thought if that was the case the set would have failed in very short order. I have worked on this set off and on for hours apon hours over many months. So before I button up the set and move on to other projects. I will take a better video of the porblem for you tube I doubt it will so anything new. If I come up with anything new I will return to this set.

Well all that work I did trying to porve it wasn't the flyback transformer was a wast of time. I took an old paper tow spol and put it up to my ear and listened and I could here little bit fant arcing and sometimes a big snapp coming from the flyback it is arching internally and yet some how it was able to run the set for many hours and it has not yet completely failed. So I'm going to try and find a flyback or another main board and if I can't the tv will run until set dies completely. Then I will part the set out.

I managed to aptan a new old stock flyback I hop it fixes it and when I get I will have to ask on how to install it as it looks like you have to plug in the anode lead into it. Flyback mad by HR Diemen

I got the new flyback and to my surprise it was made in Spain around 96. I will install it once I have sometime

An update. Good news I made some progress. the new flyback fixed the main porblem and the TV has a very sharp and nice picture still however only in black and white:no:. I do have the Sam's photo fact which dose have troubleshooting guide but it requires an oscilloscope and for time being that's a porblem. The jungle IC150 (303-1) or (NTE1416) is responsible for color processing also is responsible for the adjustment of brightness and more. The brightness is adjustable along with contrast only porblem is no color.

If you are running RF input be sure the band switches are set
to OTA TV & normal AFT.

If you are running video in check the voltages on the IC &
compare them to Sams. Look for something way off. One
of the pins will go to the color level control. That varies with
the control setting....... Be sure the IC is running cool.
Should only get warm while running not HOT.

Zeno:smoke:

The TV is RF only and I had it set to normal ( not Cable). The AFT has no user control adjustment. However it does have a control on the board labeled AFT

Still trying to figure out the color porblem. In the Sam's it has this information about troubleshooting the video buffer/Comb filter which this set doesn't have so I skipped that part. Also I did test Q153 and it was good. The AFT is done between the first video and the microprocessor on the MCU tuning system and there is no adjustments for AFT. Before I continue I have been using a Sega Genesis with the OEM RF adapter. The game system with the adapter works on all of my other TVs with RF adapter perfectly fine. There is now way to turne of the AFT but I think there might be adjustment I will need to look in the Sam's. However I don't think tunner and the video If are bad as I get nice picture with no snow or interference and clear sound just no color at all purlye monochrome as if the color killer is always on. There is no adjustment for the color killer so can't tell if that's giving a porblem. I'm afraid when it comes to color TV circuitry I'm pretty losed. I have included parts of the schematic that center around the IF and the NEC 303-1 IC. I like figuring things out on my own but I have spent hours looking at schematic and testing some parts I thought might be bad. Maybe someone will find something I overlooked. If not I will just try swapping out the NEC 303-1 chip with an NTE1416 if nothing changes then back to the drawing board. I know to most me talking about this

Thats all folks

I got the part and installed and no change so the original chip is good and the controls test good I will attempt to use my oscilloscope to see if there is any color signal making it to the ic.

Did you check those IC DC voltages ?
You may want to see if you can find a data sheet.
Any MFG markings on it ? The OEM is probably 612303-1 (?)
You also have the NTG / ECG numbers. There was a backwards ECG disc
it could list every sub. Maybe its out there still. With that you can find
the REAL OEM for the chip & data sheet.
BTW I probably have a C-5 training manual. It would cost apx a 12 pack of
beer via PayPal PM if interested but try those voltages first.

73 Zeno:smoke:
LFOD !

I will go check the DC voltages on the IC but first i did what the Sam"s said to do and that is scope PIN 13 of the IC. i got a new oscilloscope but i never took it out of the box as was going to be moving soon but i finally broke down and took it out of the box and tried it out. The results are in the video link and i have never used an oscilloscope before so the results may not be usable.
The video is not of the best quality but its best me and my grandma could do and my phone camera is not very good. https://youtu.be/2Jepwuym8AQ

here is the datasheet for the NTE1416 https://www.nteinc.com/specs/1400to1499/pdf/nte1416.pdf was not able to find the one for the original NEC 303-1

DC measurements on IC NTE1416 or NEC 303-1.

PINS 1-28 IN DC VOLTS
PIN 1 VCC 12V
PIN 2 Clamp Filter 8V
PIN 3 Brightness Control 8.7V
PIN 4 Resolution Control 6V
PIN 5 Luminance Input 2.5V
PIN 6 Peaking Filter 2V
PIN 7 Tint Control 6V
PIN 8 Auto Set Voltage 3V
PIN 9 Color Control 6V
PIN 10 Contrast Output 8V
PIN 11 Chroma Output 8.5V
PIN 12 Bypass 2V
PIN 13 Chroma Input 1.2V
PIN 14 GND
PIN 15 APC Filter 9V
PIN 16 APC Filter 9V
PIN 17 APC Filter 8.5V
PIN 18 Killer Filter 8V
PIN 19 APC/ACC Input 4V
PIN 20 Gate Pulse Input 300mv
PIN 21 OSC 8V
PIN 22 OSC 3.2V
PIN 23 OSC 3.2V
PIN 24 Blanking Input 1V
PIN 25 Demod Input 3V
PIN 26 R Output 2V
PIN 27 G Output 2V
PIN 28 B Output 2V
All voltages match the Sam's

Update March 29. I did mark the AFT adjustment located on the main board and tryed to adjust it made no difference to the color but did improve the picture quality by a hair. Next I checked to make sure the color and tint control had a good connection between the main board and the user control board. Had no problems there. Next i checked the components on the input of pin 13 on the chroma luma processor chip could not find anything wrong with any of components. Not sure we're to go next but if someone would be willing tell me what troubleshooting they do for a tv that has color not working or can point me to were I can obtain the information. I have done a lot with this TV and I don't want to give up on it as feel it has some many good years left but I have worked on it for 8 months so I'm getting tried of working on it and I am kinda in rush to get fixed as I'm moving on May 9. If the TV is not fixed by then it will be a long while before I can get back to it.

Certainly is a hope... is alreaby woking before :D
The color vanished only after changing flyback, or when you changed components or resolder?
If only was after flyback change, maybe the pulses derived from flyback have different amplitude, upsetting circuits depentent form it, if flyback is a equivalent?
And, a very small invisible solder splotch/blob can maybe ocurred at some position (washing the PCB with isopropyl alcohol using a hard brush may solve it).

Did some DC mesmurmnts on the video IF IC and I got some concerning results

Here they are
PIN 14 should be between 7.6-11.5 volts I'm reading 6.7volts IF AGC . PIN 14 splits between a 6.8kohm resistor and a .0027 cap which then goes to ground. After the 6.8kohm resistor it goes to a .047 cap and then to ground.
PIN 12 should be 5 volts I'm getting 3.7 with a full image on screen and 3.3 with no image this pin goes out and spilt between the sound IF and then goes to video buffer transistor Q153 on the collector is 6.6v, the base is 3.3v, and the collector is 2.6volts. the voltages should read base 4.8v and emitter 4.3v. after this transistor it goes to a .001 cap then to 1k ohm resistor then to splits between C175 which is a 39pf cap and L154 to ground. After C175 it spitls again between C176 82pf and L177 to ground. Finally it enters pin 13 chroma input of the chroma and luma processer IC. I don't know if this would case a B/W picture but I thought I would check.

The new flyback is an HR diamond so it's not an original. On terms of the color loss it's not a solder bridge as I changed all the caps and resolder the entire board that was done a while ago and it didn't have any trouble until now. When I still thought it was the PSU I took a couple of transistors out test and put them back. I did breck one transotor it was Q457 cupler driver which as porbly guess to horizontal optic cupler IC 469 (PS2021). I did use the NTE replacement for that transistor.

For what it's worth, the only aftermarket replacement flys that were any good IMO were the H.R. Diemens. They cost as much or more than OEM but I'd buy them when the OEMs stopped supplying flybacks and HV Splitters (RPTV). I never had an issue with any, and never had one fail.

Others (like Asti Magnetics) were hit and miss. Some worked fine, but others required modifying the circuit (Zenith) to get them to play nicely with the sweep and shutdown circuits.


John

Well that's nice to know that HR diemens made good quality stuff as not all aftermarket parts are junk but unfortunately a lot are. Now if I can find the part that is giving me trouble.

Is not very common, but I see one time or another semiconductors damaged by the flyback sparks (especially IC), even at some distance (due to EMP). Last time it occured to me was with a Toshiba TV that made a lot of sparks due to bad HV connector plus a lot of dirt. A IF IC died.