Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Col...

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Back in February or March of 2010 the TV began changing from any channel to
 channel 2 intermittently.  Sometimes very frequent.  Other times more inte
rmittent but it would not go more than a few hours without the problem popp
ing up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ckt  
but no help.  Remote control IR circuit not the problem as I disabled it.  
Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Have
 schematics and service manual but can't isolate the problem.  Nice picture
 and everything else works fine.  Unit in storage but every 4 months or so,
 when I see it and think about it, I fire it up. Hate to trash this old tv.
  Kind of part of the family now.  Has anyone ever heard of this before?

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On 29-6-2017 23:02, snipped-for-privacy@cfl.rr.com wrote:
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Spurious interference from modern light source?
Some cheap ones produce a lot of garbage besides light.

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?


Did you try disabling the keyboard?



Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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Wow, haven't seen one of these in decades.

If this model has a manual on/off switch, check the reset circuit for the micro.


Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
snipped-for-privacy@cfl.rr.com wrote on 6/29/2017 5:02 PM:
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A friend had one of those big console TVs that would work, but there was  
something wrong with the controls, I don't recall just what exactly.  I  
suggested he unplug the set for a while to let the caps drain off and the  
processor reset.  It worked sure enough!  I expect a power spike of some  
sort glitched the processor and it was working, but some variable was hosed  
messing up the operation.  A clean reset got everything working right again.

I guess that's not your problem.

--  

Rick C

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
snipped-for-privacy@cfl.rr.com wrote:

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Does it have channel up and channel down buttons on the panel?  Since  
channel 2 is the lowest channel, if the channel down button was occasionally  
acting like it was pressed, it might end up at channel 2.  I had a computer  
LCD monitor that had a soda splashed on the panel, and it got into the front  
panel button board, and it would work for months or days and then start  
flashing through the menus.  Severe cleaning of the board with the buttons  
fixed it.

Jon

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, 29 June 2017 22:03:35 UTC+1, snipped-for-privacy@cfl.rr.com  wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?

Yes from neon channel selector sets, touch selectors & older pushbutton bar
 tuning sets. Show us the circuit.


NT

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Friday, June 30, 2017 at 2:51:21 AM UTC-4, snipped-for-privacy@gmail.com wrote:
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l to channel 2 intermittently.  Sometimes very frequent.  Other times more  
intermittent but it would not go more than a few hours without the problem  
popping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection  
Ckt but no help.  Remote control IR circuit not the problem as I disabled i
t.  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  
Have schematics and service manual but can't isolate the problem.  Nice pic
ture and everything else works fine.  Unit in storage but every 4 months or
 so, when I see it and think about it, I fire it up. Hate to trash this old
 tv.  Kind of part of the family now.  Has anyone ever heard of this before
?
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ar tuning sets. Show us the circuit.
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Hmmm... you're drudging up long forgotten memories.  Back in the late 70s Z
enith used a varactor tuned electronic tuner that used neons as indicators  
for the pre-set push button selector, and sometimes those neons were the ca
use of the TV jumping channels or refusing to engage a selected channel.

By 1984 I would think that all manufacturers would be using a true digital  
selector system for anything no using a mechanical tuner.  

Unfortunately, OP didn't say if the TV would scan downward to channel 2 or  
jump to it.  He also didn't say if the TV normally defaulted to channel 2 w
hen the TV was powered off or when the AC was lost.

There were a lot of TVs then that used a digital keypad, but were not remot
e control and used a mechanical AC switch and volume control.  In this case
, it's possible that the uPc is only used for channel functions and his pro
blem could be on the micro's reset line.


Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Friday, 30 June 2017 12:29:30 UTC+1, John-Del  wrote:
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nel to channel 2 intermittently.  Sometimes very frequent.  Other times mor
e intermittent but it would not go more than a few hours without the proble
m popping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selectio
n Ckt but no help.  Remote control IR circuit not the problem as I disabled
 it.  Over time have replaced some bad unrelated hw (burnt resistor, Caps).
  Have schematics and service manual but can't isolate the problem.  Nice p
icture and everything else works fine.  Unit in storage but every 4 months  
or so, when I see it and think about it, I fire it up. Hate to trash this o
ld tv.  Kind of part of the family now.  Has anyone ever heard of this befo
re?
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 bar tuning sets. Show us the circuit.
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 Zenith used a varactor tuned electronic tuner that used neons as indicator
s for the pre-set push button selector, and sometimes those neons were the  
cause of the TV jumping channels or refusing to engage a selected channel.
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l selector system for anything no using a mechanical tuner.  
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r jump to it.  He also didn't say if the TV normally defaulted to channel 2
 when the TV was powered off or when the AC was lost.
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ote control and used a mechanical AC switch and volume control.  In this ca
se, it's possible that the uPc is only used for channel functions and his p
roblem could be on the micro's reset line.

Until the OP tells us what the technology is we have really no way to advis
e usefully. 1984 could be a few things, switched linear pots with varicap i
s likely, or touch sensors maybe. There were also old technologies used in  
some sets, so can't completely rule out a mechanical selector device operat
ing a tuning bar.


NT

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
http://diagramasde.com/page/2118

Might be something usable here.  

My S.W.A.G. guess based on similar-vintage technology failing-to-default is a weak capacitor that does not hold the charge necessary to 'latch' to the chosen channel.  

Peter Wieck
Melrose Park, PA  

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
Most likely it is going into reset. Does it hold your settings, like color,
 brightness and whatever ? Probably not. They are likely all going to facto
ry reset.  

That would mean you are losing power to the micro or maybe the memory IC, o
r the memory IC is defective. Ir it has a memory IC it is probably an eight
 pin EEPROM. Look at the board and see if it has a supercapacitor or whatev
er, or a battery. Those could well be failing. That is actually more likely
 than an IC failing.  

Keeping this old shit running is a good thing because all the new stuff is  
junk. My Ma watches an old CRT based Toshiba which works just fine. I do no
t have a TV hooked up because the programing is all junk. The scene changes
 so fast you cannot see anything. PUT THE IMAC DOWN ! Anything I want to wa
tch is old.  

One question here - does it return to channel 2 as you are watching it ? If
 so, that means there is a temporary interruption in the power supply, prob
ably the standby supply. That would make me suspect a bad connection, or ma
ybe one inside of a device like a regulator or something.  

It can also be caused by low supply voltage to whatever holds the memory. I
 would be headed for the power supply.

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thu, 29 Jun 2017 14:02:39 -0700 (PDT), snipped-for-privacy@cfl.rr.com
wrote:

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I ran the  television service department in the corporate headquarters
for the largest seller of Hitachi sets at that time in the U.S. so I
might be able to help you. First disconnect pin 17 and 18 of IC0102
and see if the problem disappears.  If so, then it is likely the
channel tact switches.  If not, take freeze spray and a hair dryer to
the tuner.  The two main failures in this model, when there were tuner
problems, were the ic you replaced and the tuner itself.  The band
switch IC IC0104 occasionally would fail and any 2SC458s in the
circuitry can cause problems. If these checks don't work, post again
and we'll go deeper in depth.  Chuck

---
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Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase

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Also replace C703 and R703 (off the flyback) if the previous hints
don't work.

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase

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Ignore my last post; I followed a wire incorrectly.  These parts are
in the XRay shutdown circuit and do not pertain to your problem.

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?

----------------------------------------

I want to thank all of you for your time and comments.  Here is some feedba
ck to you:

Ultimately I would be fine if the only two channels I can get are 3 or 4 fo
r my direct tv cable.  Can?t live with channel 2 though.

The tv will go to the channel you select using the key pad or remote (befor
e I disabled the remote).  As you watch your chosen channel it will instant
ly change to channel 2 and not scroll to it.  

I can?t imagine a light source being the problem.  The IR receiver  
works but was disabled to rule this out. While it was disabled the tv would
 still change to channel 2.  No suspect rf sources in vicinity either.   Pr
oblem happens in any room.  The most exotic rf source I have are is my comp
uter, monitor and microwave.  No ?new? technology stuff and
 problem happens with computer and monitors off.  No supercapacitor or batt
ery for backup and not listed in parts.  I don?t see any central mi
croprocessor in the schematics or parts list that applies to this model and
 chassis.  The CT1957 model has a Channel Selection memory IC IC0103 (MN122
8) but this model CT1955 does not.  The circuit board has an empty spot for
 this 18 pin IC.  

Unit has buttons for channel/volume up/down and power.  All the picture/vid
eo controls are adjusted using potentiometers located behind a flip down pa
nel at the bottom center of the front of the unit.  No mechanical selectors
 other than the video pots.

Your feedback was excellent so I power up the unit for the first time in mo
nths and it defaulted to channel 2.  I set up some tests.

Test #1 Sequences:
?    Power on change to channel 5 and set volume to 15
?    Power off button when not having problem.   Power back on channel
 is at 5 and volume at 15
?    Power off button, when not having problem, and remove power cord  
from ac: Plug back in and power up:  Channel = 2 and volume = 21.  I th
ink this is normal.
?    Power on and set to CH5 / Vol15%.  
?    While not having issue I pulled power cord without depressing pow
er off button: Plug back in and power up:  Channel = 2 and volume = 21


Test #2  Rear Switch Settings (S1 3-Way Switch): My default settings are CH
=5 / Vol15%  

S1= Either CATV1 or CATV2:  Monitoring TV unit CH=5 / Vol = 15.   Wit
hin 2 hours of power on the problem occurred and then it started occurring  
frequently.  The tv Changed to channel 2 from 5 instantly and the volume st
ayed at 15.  It did not change to 21 as what happens when ac is removed fro
m the unit.

S1 = ?Normal?  (VHF/UHF) :  Problem does not happen.  Swi
tching back to CATV1 or 2 problem happens within minutes.  Put Switch in  
?Normal? mode.  No problem for next hour+, up to the point  
of posting these notes.  If this holds I?m good.  I will leave S1 i
n ?Normal? mode and powered on for hour or days until I hav
e confidence in .   .  . . ?..     something.

Tried freezing and heating the tuner and components but no impact.  I thoug
ht I ruled out the keypad but can?t swear to it.  Will check.  No n
eon?s.

From my last troubleshooting notes:

6/9/16  Per T/S flow chart ordered and replaced items below including an in
coming power electrolytic 22uF/250v.  Not related to problem but has a dome
d top.  :  

?    IC0102    MN14834HH         High hopes?.  Big letdown??
??

?    Socket for above

?    Q102         2sc458 B/C/d      2sc1740Q/R

?    Q0103     2sk105 E/F

?    Q0104     2sc1213A  

?    IC0104    LA7910        Band Drive         Ordered and have part but did not rep
lace

?    ZD0101    Measured OK:    RD33EB1        ZD HZ6(C)1    


If problem happens with S1 in ?Normal? mode I will replace  
IC0104 (Band Drive) and get to the remaining 2SC458?s later.  There
 is a 5v Regulator powering IC0102 I?ll  try to get that monitored  
also

Just looked at original receipt.  Purchased in 1986 not 1984  $356.  

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Mon, 3 Jul 2017 14:54:30 -0700 (PDT), snipped-for-privacy@cfl.rr.com
wrote:

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The set didn't come on the market in the U.S. until 1985. If all you
need is channel 3 and it doesn't do it with the switch in the normal
mode, I'd just leave it be unless you are just curious to know the
solution.  I don't have the schematic in front of me because I am on
vacation but doesn't that normal - cable switch also have a HRC
position?  I'd  be curious if it goes to 2 in that position.  If it
doesn't I'd clean the switch, it possibly could be the problem.  Chuck

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase

On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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MN14834HH is processor, check oscillator (pins 36/37) and  reset voltage  
(pin 39).
Replace resistor RO125 and DO110 (on pin 6).  



Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?

No STD, IRC or HRC position switch or other type of such options.  Just the
 single 3-position switch: CATV1, CATV2 or Normal.  TV has been running for
 more than 24 straight hours in the ?Normal? switch positio
n mode and has not changed to channel 2.  

Moving 3-way switch to position:

CATV1    TV switched to channel 2 in a few seconds  
CATV2    Waited a few minutes but it did not change this time
Normal    Steady

When switch is moved to one of the three positions the tv defaults to CH2/V
ol21%.  I cleaned the switch and all is stable while I type these notes.  
 Will monitor and report out.

Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?

Thanks for the info.  I'll add it to my troubleshooting short list.  I clea
ned the switch S0125 on 7/3 and the TV has been running solid through today
 7/7.  This has been the longest period without the problem since it first  
popped up in 2010.  The TV is now back in action on its shelf in the kitche
n area.


Re: Old Tube TV Keeps Changing Channel to Channel 2: Hitachi CT-1955 NP85XA Chassis / 19" Color-1984 Purchase
On Thursday, June 29, 2017 at 5:03:35 PM UTC-4, snipped-for-privacy@cfl.rr.com wrote:
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to channel 2 intermittently.  Sometimes very frequent.  Other times more in
termittent but it would not go more than a few hours without the problem po
pping up.  Replaced IC0102 (MN14834HH) Main IC for the Channel Selection Ck
t but no help.  Remote control IR circuit not the problem as I disabled it.
  Over time have replaced some bad unrelated hw (burnt resistor, Caps).  Ha
ve schematics and service manual but can't isolate the problem.  Nice pictu
re and everything else works fine.  Unit in storage but every 4 months or s
o, when I see it and think about it, I fire it up. Hate to trash this old t
v.  Kind of part of the family now.  Has anyone ever heard of this before?

8/26/2017  One final note. It's been over 6 weeks now and the tv has worked
 fine since cleaning the 3-way switch.  I guess it's fixed.  Thanks for all
 your help guys.


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