Free TV Schematics

[Robert Reed]

I have an RCA 9" color TV circa 1995. It uses the "instant on" feature and lately has been acting up. It wont turn on unless unplugged for 15 min. and the restarted. Unfortunately, it loses all it memory for settings when this is done. Does any body know of a website for free TV schematics. In the past the ones I have priced have been in the $25- $45 range - way too much for the value of this set. I thought I had seen some free sites while surfing the web in the past, but cannot seem to relocate them.

[wd5gnr]

Never can tell about finding a specific model but: http://www.schematicsforfree.com/ might help you.

[sofaspud]

I'd give eServiceInfo.com a try too.

[Janitor Tzap]

Hey Robert,


Have you checked with your local Libraries to see if they carry the SAMS PHOTOFACTS?

One of my Local libraries has them going from 1958 to 1999.

If you do have a library that does.
Get the model number off the back.
Check the SAMS PHOTOFACTS website.
http://www.samswebsite.com/photofact/pf_search.asp
Take down the SAMS number, and check if the library has it.
Then just go down there and make photo copies of it.


Signed: Janitor Tzap

[Robert Reed]

Hi guys
I checked the first two web suggestions and nada on this model. I my web travels anything that came up was intertwined with Thompson or Saga, but none of it made sense anyhow. I think most TV sets in the last decades come from a ship from Asia directly to RCA for a brief stopover to put the company name on it and then off to the retailers. Who knows who the OEM was.My recolection from years back was that RCA chassis nos. were always CTC xxxx and this one is no where near that.
Jan
That is my next step to check and see if there is a Sams print on this, my thinking being if they don't have it then nobody does. Unfortunately there are no LARGE libraries near me - or are they all connected by computer now that one could download from a local branch? The last Sams I bought was real high priced. Maybe they can e-Mail a cheaper version now.

PS cool- we have spell check now. When did that take place?

[Bob Scott]

Never can tell about finding a specific model but: http://www.schematicsforfree.com/ might help you.

<NAB!>

I'd give eServiceInfo.com a try too.

<NAB!>

Thanks guys! Those have some good older diagrams.

[Janitor Tzap]

Hi guys
I checked the first two web suggestions and nada on this model. I my web travels anything that came up was intertwined with Thompson or Saga, but none of it made sense anyhow. I think most TV sets in the last decades come from a ship from Asia directly to RCA for a brief stopover to put the company name on it and then off to the retailers. Who knows who the OEM was.My recolection from years back was that RCA chassis nos. were always CTC xxxx and this one is no where near that.
Jan
That is my next step to check and see if there is a Sams print on this, my thinking being if they don't have it then nobody does. Unfortunately there are no LARGE libraries near me - or are they all connected by computer now that one could download from a local branch? The last Sams I bought was real high priced. Maybe they can e-Mail a cheaper version now.

PS cool- we have spell check now. When did that take place?

Have you checked inside the case?
RCA/GE/Thompson will normally have a CTC XXXX number on the main board.
{Plaster onto the side of the tuner pack.}

Also, Samsung made a lot of the smaller sets for GE/RCA/Thompson.
Thus, I sometimes found the schematic in a Samsung set that was basically the same.

Hmm.....
RCA main boards are notorious for bad solder.
But, from the symptoms your describing.
I'm thinking that the problem is in the 5Vdc supply for the remote function.
More than likely a filter capacitor.


Signed: Janitor Tzap

[Robert Reed]

Have not opened up the set yet, but if no prints can be located reasonably, will do that soon and check for PNs. I remember that the early "instant ons" simply maintained a low CRT filament voltage while the set was turned off. It appears on this one, that programmed memory must also be maintained by a constant lo volt supply. The set has an on/off switch on the front panel, but this may just be a momentary switch parelleling the IR input circuits.

[CeaSaR]

wd5gnr,

Your link has a schematic I've been looking for since '92 when I lost my copy of the April issue of Radio Electronics.

Sofaspud,

You too! Found some possibilities there!

Thanks guys,

CeaSaR

[Robert Reed]

Further research
Chassis no. is TX825QC. SAMS has it and was quick to locate, so that is a valid no. Cost is $22 E-Mail and does not print up well with less than 11x17 paper. Cost is $36 print version. Too much money to lay out where I may find out the defective part is not available or if it is may be so expensive that it shoots down the whole project. I guess its time to open this bad boy up and see if anything evident shows up

[Janitor Tzap]

Have not opened up the set yet, but if no prints can be located reasonably, will do that soon and check for PNs. I remember that the early "instant ons" simply maintained a low CRT filament voltage while the set was turned off. It appears on this one, that programmed memory must also be maintained by a constant lo volt supply. The set has an on/off switch on the front panel, but this may just be a momentary switch parelleling the IR input circuits.

The "instant ons" TV's that were produced in the late 60's to early 70's had the low current flow circuit to the CRT's Heater Filament.
Thus, you would get almost instantaneous picture when you turned on the television.
But unfortunately these sets were fire hazards, because the low current Filament Resistor would break down.
I had to disable a lot of those "instant ons" circuits because of that.
The CRT manufacturers then came up a faster heating filament.
These were used more in portable battery TV's.
But by the end of the 80's the most CRT's were using the faster heating filament.

The channel settings are being lost every time power is lost.
Hmm......
That's strange.
Normally there is a "Memory Cap", or even a small nicad cell.
It is there to hold the memory for at least 2 hours max for limited power interruptions.

Well, have fun poking around in it!


Signed: Janitor Tzap

[Darrell M]

Hi Robert

I have repaired a few of the RCA TX825 tv,s with the symptom of not wanting to turn on. I have always found it to be a bad standby regulator transistor TP15. It is easy to spot because the heat from it has darkened the pc board. Its collector is fed by unfiltered pulses through some resistors from the "cold" side of the AC line and regulates to about 10v in standby mode, then it feeds a 5v regulator transistor. The RCA part no. of TP15 is 198752 which I've never found a cross reference for, but I've been using a 2SD986 which is a higher power darlington and seems to work fine.
I have a Sams PF for a TX825TC which is probably similar to your TV. If you need more information I could send you a copy.

Darrell M

[Robert Reed]

Thank you Darrel for your most generous offer. Before I put you to the trouble of print copying,etc. , I will open the set up and inspect that area mentioned. Would that area be near the AC line input? If not that, I will get back to you.

[jimmy101]

Have you searched for just the part number without "schematic" (or similar words)? Often you can find the exact problem on the exact set. I've had luck finding things like how to fix bad vertical drive on a 15 year old set with details all they way down to which caps and which chip to replace. (Actually finding them on the circuit board took forever though.)

If you have a chassis number, or can guess at what similar model numbers might be, you greatly increase your chance of finding what you want.

You can also just search with the manufacturer name and words describing the problem. Often that'll find similar sets with the same symptoms which often have the same solution.

(There is a good chance you have already done this, if you have, it should have been noted in your posts. Searching for a solution to a problem is not the same as searching for a schematic.)

[Bob Scott]

The "instant ons" TV's that were produced in the late 60's to early 70's had the low current flow circuit to the CRT's Heater Filament. Thus, you would get almost instantaneous picture when you turned on the television. But unfortunately these sets were fire hazards, because the low current Filament Resistor would break down.
I had to disable a lot of those "instant ons" circuits because of that.
Signed: Janitor Tzap

During the early '80s, I attended one of RCA's VCR repair seminars. They were warning against replacement of flameproof resistors with other types. These flameproof resistors had 4 little holes in each end around the lead wires. Although flameproof resistors are apparently made and sold by Vishay, I have not seen any resistors with holes for a long time.

JT, here's a link to flameproof resistors if you or anyone is interested:
http://www.repairfaq.org/samnew/tvfaq/tvflamepr.htm