RCA CRT TV - Chassis CTC169CF

[Brian1234]

Hi all,

I've found great help in the audio forums here and have a TV repair project where I could use some input. It's an RCA model F27227EM with chassis number CTC169CF. The symptom is 'no power', more specifically it blows the internal fuse as soon as it is plugged in (not even turned on).

I immediately noticed that the movistor(?) in the power section was detached from the two wires that were suppose to be soldered to it, and was still in place only because the wires had it trapped.

I've now pulled the 4 bridge rectifier diodes and they measure infinity in the reverse direction, but 10Mohms in the forward direction when I should be seeing 0. I have also pulled the 200v 680uf electrolytic (C7K?) in the same area and it seems to measure 0uf on my multimeter but is not shorted.

I'm working without a schematic though, so I'm working more by deduction than facts. The 2.7ohm 15W resistor tests OK in circuit, and everything looks OK visually.

So my questions to anyone familiar with this stuff or with a schematic, are there any other parts in that section I should check? Do you think I got it all, or am I likely to blow up new parts in search of something bad further down the path... maybe the TV isn't worth the trouble? What about the 180v 47uf cap, do I need to pull that? Kind of a pain to get to.

Thanks!

[Eric H]

Check out this link:
http://www.audiokarma.org/forums/sho...ghlight=ctc169

some good info on troubleshooting this problem on the 169!

[Brian1234]

Lots of good info there, for sure. However that looks like a different problem, my 2.7ohm 15W is OK and the rectifier diodes are bad. I'm wondering of perhaps the 200v 680uf went bad and took out the parts in front of it. I don't have a lot of time to spend on this right now but if the problems are in the linear section before the switching stage then I might be able to handle it.

[radiotvnut]

Those diodes are probably good. If you are using a digital meter, check them on the diode scale. The likely problem is the chopper transistor (mounted on a heatsink) in the power supply. This transistor likely took out the control IC. In addition, replace the electrolytics in the switching circuit. 39uf, 2.2uf, 15uf, and 470uf. They are all located right there around the IC and transistor. And, check the horizontal output transistor for shorts. It's on a big heatsink close to the flyback transformer.

BTW, don't use NTE, ECG, or any Chinese knock-off parts in this application because they likely will not hold up. Use original RCA parts if possible. www.tritronicsinc.com should have the parts.

IMHO, the CTC169 was the best Thomson era RCA chassis made.

[Brian1234]

I had also flipped over to the diode scale while I had them hooked up (no beep in the forward direction). How could they be good if I measured 10Mohms when it should be (near) 0? Either way they're useless now, I clipped the leads then unsoldered the ends. (heh)

The horizontal output transistor is on the big heat sink in the middle of the board... looks a lot like the chopper transistor?

[radiotvnut]

Originally Posted by Brian1234

I had also flipped over to the diode scale while I had them hooked up (no beep in the forward direction). How could they be good if I measured 10Mohms when it should be (near) 0? Either way they're useless now, I clipped the leads then unsoldered the ends. (heh)

The horizontal output transistor is on the big heat sink in the middle of the board... looks a lot like the chopper transistor?

Yep, it's in the center of the board and looks like the chopper transistor. If you check it in circuit, it will show a short between the two end terminals. This is normal. If you measure a short between either one of the end terminals and the center terminal, you have a shorted HOT. If the HOT is shorted, look for a swollen rectangular cap (usually blue) close to the HOT. Maybe you'll get lucky and it will just be the power supply components. And, don't worry about the rectifier diodes. 1N4007's are cheap. I usually order them by the 100.

[Brian1234]

Originally Posted by radiotvnut

If you measure a short between either one of the end terminals and the center terminal, you have a shorted HOT.

I didn't get a chance to do anything on it today but if you have a test like that for the chopper transistor section, let me know so I can do it at the same time.

Thanks a ton

[radiotvnut]

Originally Posted by Brian1234

I didn't get a chance to do anything on it today but if you have a test like that for the chopper transistor section, let me know so I can do it at the same time.

Thanks a ton

Generally when that chopper shorts, you will read almost zero ohms (a dead short) on all three terminals. If it's shorted, go ahead and change the controller IC and the caps.

[andy]

000

[MRX37]

Originally Posted by radiotvnut

IMHO, the CTC169 was the best Thomson era RCA chassis made.

Um, my CTC158B chassis is pretty damn good. The only thing to really fail on it so far was the degaussing thermistor.

[tmwalsh]

Check http://www.acme-sales.com/ for a SMPS kit at $8.95. Tritronics was down to one in stock a few months ago, and seemed to not be restocking as only one warehouse had anything on hand.
You can go to eserviceinfo.com and download a .EXE file for CTC-169 that has some good hints:
http://www.eserviceinfo.com/download...A_proscan.html

Progam: R2456d.exe

Save it, run it, and don't enter a password when asked. Very nice graphic help.
tom

P.S. I bought mine in 1992, got another on election day, and have my little sister's 1995 model that she left on her leaky back porch for several years... The only problem I have is her audio muted, I replace the amplifier IC, and lifted a resistor to disable the mute. Went kapow every time we turned it on, and finally shorted the amp. Still working on that one.
tom

[Brian1234]

Originally Posted by radiotvnut

Generally when that chopper shorts, you will read almost zero ohms (a dead short) on all three terminals. If it's shorted, go ahead and change the controller IC and the caps.

Yup, that looks like the trouble. The HOT seemed OK, just showing a short across the outside terminals.

andy: Ah, indeed they showed about .5v when tested in diode mode... I had thought that would be enough to overcome the forward voltage drop.

tmwalsh: That acme link seems outdated. What does SMPS stand for? Thanks to the link for the exe file!

[radiotvnut]

I think you'll get off light with this one. Just replace the chopper transistor, IC, and caps and it should be ready to go. And remember, DON'T use NTE parts in this application. They'll bite you in the butt in short order.

SMPS = switch mode power supply.

[Brian1234]

OK, I'm taking another look at this... it'd be rewarding if I can get it going but it's only worth so much time and money.

Here's the parts list I have so far:
Transistor RCA # 200165, generic # SGSIF461 (RCA)$19.39
IC RCA # 200419, or TEA2261 (RCA)$13.19 (RCA/TEA)$2.92
Electrolytic: 39uf (replace with 47uf @ 50v?)
Electrolytic: 2.2uf
Electrolytic: 15uf
Electrolytic: 470uf
(4) Diodes: 1N4007(?)
At the tritronics site however I find it difficult to ID the cap and diode parts... do they sell these or would I have to go through digikey or similar (raising the price due to more shipping)? All 4 caps in the area near the IC look like polarized caps but I thought I heard one was a non-polar? Anyone better at finding order #'s for these than I am?

The 2.7 Ohm / 15W resistor measures 2.5ohm in-circuit... think that means it's ok?

What is the disc unit underneath the 2.7 resistor... an MOV? I happen to have an NTE524V15 on hand, is that a suitable replacement?

[Edit] Is there anything else I should look at, as listed at:
http://www.freelists.org/post/techas...d-fuse-blown,3

Thanks!

[kx250rider]

There was, at one time, a whole kit containing those parts in the previous post, and some others. I remember having a lot of callbacks on those sets if I didn't do the whole job. However, no callbacks when I did!

If Fox International is still around, or MAT Electronics, the kit may still be available. It was about $16.

Charles