View Full Version : Found this on the side of I-840 today, Magnavox console tv.


mr_fixer
01-05-2017, 07:47 PM
Hi all! on the way home i saw this sitting on the side of the interstate. It doesn't look dropped or scarred up. It is a Magnavox 25C549 chassis, made in Greeneville TN, USA Jan of 1986. i powered it up but doesn't come on, i hear a faint buzzing sound from the chassis, anyone have a schematic for this set?

Findm-Keepm
01-05-2017, 09:59 PM
Hi all! on the way home i saw this sitting on the side of the interstate. It doesn't look dropped or scarred up. It is a Magnavox 25C549 chassis, made in Greeneville TN, USA Jan of 1986. i powered it up but doesn't come on, i hear a faint buzzing sound from the chassis, anyone have a schematic for this set?

Lemme check - I may have the NAP manual - have 5 or 6 binders full of NAP stuff. I'll check tomorrow, before the snow dump we have coming. I also have service tips for the set as well - most are NAP sourced...

Jon A.
01-06-2017, 12:20 AM
Nice catch! Unusual place for a console TV to get dumped, even more unusual that it's not beat up, or that it even survived.

kf4rca
01-06-2017, 07:58 AM
Somebody running low on gas must have decided to lighten their load. Finders keepers, losers weepers!

Findm-Keepm
01-06-2017, 08:28 AM
I've got the service lit - most of it. I have the model specific data and the supplement with schematic, parts list, breakdown list and interchangeability data. I also have the Switchmode power Supply manual (theory, general operation, a must for the "bitch mode" supplies these have...) from NAP, all yours for postage. PM me your address, and I'll get it out to you.

In the meantime, do you have 130V across the diode (D404) on the yoke? Negative lead to the anode (hot ground...)That was always our starting point - D404 is a high-failure item in these chassis, and my earlier attachment provides a list of stuff to check as well - lots of bad solder jobs on the early runs of these chassis - the 25C55X series didn't seem to have the solder issues, just the earlier 25C53X and 25C54X stuff.

January 1986....when the Challenger tragedy struck.....

DavGoodlin
01-06-2017, 09:47 AM
I too cannot let such a good example like that just sit. I always find them a home. Hats off to you!

I worked for a dealer then and remember that as the mid-level set. A one knob-tuned with UHF presets was the entry level.

dieseljeep
01-06-2017, 10:55 AM
Lemme check - I may have the NAP manual - have 5 or 6 binders full of NAP stuff. I'll check tomorrow, before the snow dump we have coming. I also have service tips for the set as well - most are NAP sourced...

We had a considerable amount of snow, a lot of it melted in the unseasonable warm weather, but now we're paying for it. Zero or colder, with sub-zero wind chills. The snow is just an inconvienience, but that extreme cold. :thumbsdn:

Findm-Keepm
01-06-2017, 11:58 AM
The snow is just an inconvienience, but that extreme cold. :thumbsdn:

I agree 100% ! We need a few days below freezing to kill the mosquito eggs and other pesky bugs, but please nothing near, at or below zero.....:thumbsdn:

Electronic M
01-06-2017, 12:06 PM
We had a considerable amount of snow, a lot of it melted in the unseasonable warm weather, but now we're paying for it. Zero or colder, with sub-zero wind chills. The snow is just an inconvienience, but that extreme cold. :thumbsdn:
Yeah, the snow is only an inconvenience at worst... It can be useful too. Folks at work are afraid to park in the half plowed spaces...I don't like(/worry about) my GMC much so I just run over the snow hills and park on them. Seems as soon as I do someone else will get the stones to park there after I leave for lunch. :scratch2: :D :screwy:
The cold REALLY stinks! The heater in that GMC ain't worth a damn under 20 degrees...It barely can get the car above freezing once it hits zero...engine runs real cold too. If I had better winter clothes I'd try taping card board over the grille to see if impeding cooling helps.
Saw something unusual on the way to work today...I guess it would be called a 'snowbow' since it is WAY too cold for rain...Did not know such a thing could form in weather this cold.

jr_tech
01-06-2017, 02:14 PM
The cold REALLY stinks! The heater in that GMC ain't worth a damn under 20 degrees...It barely can get the car above freezing once it hits zero...engine runs real cold too. If I had better winter clothes I'd try taping card board over the grille to see if impeding cooling helps.


Thermostat stuck open, perhaps? :scratch2:

jr

Jon A.
01-06-2017, 03:16 PM
Seems almost everyone starts hating the cold and snow upon growing up. I'm one of VERY few adults (well, chronologically anyway) who like winter. We've hardly had any snow since winter began but we're finally getting it today, and I'm thankful for it. The night I pushed the Heathkit console home it was 10 below, making the activity that much more comfortable.

davet753
01-06-2017, 04:37 PM
I remember the C5 chassis very well. It seems like they only had two types of service issues: either they were a quick and easy fix, or they sat on the bench for days while every tech in the shop pulled his hair out trying to troubleshoot it.

Findm-Keepm
01-06-2017, 07:04 PM
Thermostat stuck open, perhaps? :scratch2:

jr

Or missing.....had that on a Nissan Truck I troubleshot for a friend - A/C use would overheat the engine, so the dealership removed the thermostat. Come cold weather, he froze his hiney. Installed an OEM and no more problems, and gas mileage went up considerably......

mr_fixer
01-06-2017, 07:24 PM
Thermostat stuck open, perhaps? :scratch2:

jr
My old volvo had that problem, the thermostat failed in the open position. worked great in the summer froze till i figured it out. oh i'm thinking the H.O.T transistor has failed I tested it with my Leader in circuit tester and and it said dead. I let the power stay on for about 30 seconds and the heat sink is warm. In findem keepem's post with the helpfull hints it said the trans is a 2sd1398(8)?

Electronic M
01-06-2017, 08:02 PM
Thermostat stuck open, perhaps? :scratch2:

jr
Thanks for the tip! I'll have to check into that. Symptoms match what I've read. Replacement thermostats claim 192 degrees F is the factory open point, if the temp gauge is accurate I'm not making 150 F in 30 min of operation...IIRC the check engine code I have was traced to timing and cooling system...Time to find that sheet, and order a new thermostat.

mr_fixer
01-11-2017, 01:10 PM
PM sent,
new transistor, no change in action. I have 30 volts on the hot which i think is the start up voltage, i have 320 in a different section, but don't know enough about this weird power supply.

I've got the service lit - most of it. I have the model specific data and the supplement with schematic, parts list, breakdown list and interchangeability data. I also have the Switchmode power Supply manual (theory, general operation, a must for the "bitch mode" supplies these have...) from NAP, all yours for postage. PM me your address, and I'll get it out to you.

In the meantime, do you have 130V across the diode (D404) on the yoke? Negative lead to the anode (hot ground...)That was always our starting point - D404 is a high-failure item in these chassis, and my earlier attachment provides a list of stuff to check as well - lots of bad solder jobs on the early runs of these chassis - the 25C55X series didn't seem to have the solder issues, just the earlier 25C53X and 25C54X stuff.

January 1986....when the Challenger tragedy struck.....

Marco-nix
01-12-2017, 09:05 AM
We had a considerable amount of snow, a lot of it melted in the unseasonable warm weather, but now we're paying for it. Zero or colder, with sub-zero wind chills. The snow is just an inconvienience, but that extreme cold. :thumbsdn:



Indeed! ... I would have let it take the temperature of the room at least 3 days before turning on the television. At least, I would have dried the circuits with a hair dryer for an hour or two by going gently so as not to soften some pieces. :yes:

zeno
01-12-2017, 09:06 AM
Watch for disc caps & box caps off the C of HOT. Common
for them to burn, melt or short. Also burned PCB that
may be hidden under frame plastic. Noise is probably from
SMPS running off freq to keep the overload from wrecking everything.
Assuming HOT is not shorted see if it gets hot in 30 sec.
If so probably bad FBT.

73 Zeno:smoke:
LFOD !

Electronic M
01-12-2017, 09:52 AM
Indeed! ... I would have let it take the temperature of the room at least 3 days before turning on the television. At least, I would have dried the circuits with a hair dryer for an hour or two by going gently so as not to soften some pieces. :yes:

You sound like someone with a home humidification system! I wish I had one. Where I'm at this time of year there is just a small portable unit, and it can barely do anything...A cup of water with a napkin in it will dry in under a day.

Marco-nix
01-12-2017, 10:27 AM
You sound like someone with a home humidification system! I wish I had one. Where I'm at this time of year there is just a small portable unit, and it can barely do anything...A cup of water with a napkin in it will dry in under a day.


Yes at home temperature and humidity are controlled. But what I wanted to say is that if I find a TV out in the winter I will never turn on the TV right away because of the difference in temperature (cold outside and the temperature inside my apartment) . Because the risk of components leaping, is high. That's why I said earlier that I would wait at least 2 to 3 days before turning on a TV found on the street in winter ..It's absolutely necessary to let the circuits dry completely. Even the CRT should not be wet. If not, .... BOUM! . It happened to me once because I was too eager to see if the TV was working. Now I'm careful.

mr_fixer
01-14-2017, 11:35 PM
Hi all, I got the service manual from Findm keepm today and spent most of the day checking everything i can, to no avail. the 2 main symptoms are low voltage in the horizontal driver circuit, expected 33 volts got 6 and the 130 supply is around 21 volts. this is one of those switching power supplies that has 2 types of protection circuits over voltage shutdown and current limiting. I've taken a pic of the waveform on the switch mode regulator what i have vs what the book says it should look like, any hint on what i should try next?
Logan

zeno
01-15-2017, 12:18 PM
Unhook the C of the HOT & see if the voltage comes up. Also
do the heat test of the HOT.
Dont forget you are working with 3 grounds on this set.
Hot gnd for the primary of the PS
Cold ground the chassis ground / PS secondary.
I dont think this one does but some sets also had another ground for the
hoz osc/out.
CRT ground. Most NAPs do NOT ground the CRT dag as normal sets.
We used to just grab the CRT ground but that dont work on these.

73 Zeno:smoke:
LFOD !

zeno
01-15-2017, 12:40 PM
OOPS !
Just pulled the training manual & the hoz output is
also on the hot ground side !

mr_fixer
01-15-2017, 05:35 PM
Ok, i disconnected the hot and flyback from the 130v supply, voltage went up to 138 v, I connected a small 40w lightbulb from 130v to ground for a load, volts dropped to 27v. Horizontal driver supply voltage is unchanged at 6-7 volts where 33 is expected.
hmmmm. resistors that drop the 33 supply from 312 volts are good and there is a diode that somehow is supposed to bridge the 2x20k resistors and 7 volts worth of zener diodes to ground. I'm not sure how a regular diode can act like a resistor, any thoughts?
Logan

Unhook the C of the HOT & see if the voltage comes up. Also
do the heat test of the HOT.
Dont forget you are working with 3 grounds on this set.
Hot gnd for the primary of the PS
Cold ground the chassis ground / PS secondary.
I dont think this one does but some sets also had another ground for the
hoz osc/out.
CRT ground. Most NAPs do NOT ground the CRT dag as normal sets.
We used to just grab the CRT ground but that dont work on these.

73 Zeno:smoke:
LFOD !

RCAZenith
01-16-2017, 07:53 AM
I-840 - Nashville is an interesting place to say the least. My father was in a country band in the late 90's about 2 steps from making it big and it didn't pan out for them. I was up there for training a couple of of years ago. I don't think I met anybody the whole time I was there that was local!

I've yet to see any tvs on I-285. I bet they would be smashed to bits long before any of us were to come along. That and I try and stay out of atlanta anyways...


Sent from my iPhone using Tapatalk

zeno
01-16-2017, 09:58 AM
What you need is horz drive from IC340 pin 11
That goes to the optic isolator IC469.
VCC for IC340 pin 10 comes from T453 / D461
Hoz drive is a must have to run the PS.

Since unloaded it seems to be doing what it should
I would suspect over voltage shutdown. Maybe test the small
transistors by lifting 2 leads for accuracy.
BTW one of our distributors made up kits for these to fix
them after lightning. Worked 100%. IIRC had an isolator,
4 small transistors & a diode.

The similar C3 chassis had a lot of bad FBT's Symptoms
were dead set, HOT gets too warm, R460/461 get warm.

73 Zeno
LFOD !

davet753
02-20-2017, 07:34 PM
Be sure to check for cracked solder joints on the horizontal driver transformer. C5 was about the time Philips started using the driver transformers that had a metal pin on each corner of the frame (the windings soldered onto the top of the pin and the bottom of the pin came through the board)....it's a good idea to re-solder all 8 points.

A bad connection on that transformer will most always zap the horiz. output or more.