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Old 2nd Dec 2019, 10:29 pm   #81
19Seventy7
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Default Re: RRI T24E Chassis

I have a manual which I can scan if that's of any help?

Thanks
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Old 2nd Dec 2019, 10:34 pm   #82
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Default Re: RRI T24E Chassis

Hi JC
Here are two equivalent Toshiba models for the Rank T24

Toshiba C2225B1
Toshiba C1695B1

This was C/O the TV mag, so I cannot vouch for the accuracy.

We saw a couple of the RRI T24 models back in the day, apart from fairly obvious faults they seemed to be fairly reliable.

One fault in particular with these models stands out in my memory, and that is a strange swirling pattern over the picture, this was caused by the main block going O/C, a couple of later Tosh only models also suffered from this problem later IIRC.
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Old 2nd Dec 2019, 10:38 pm   #83
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Default Re: RRI T24E Chassis

A scan of the manual would help enormously
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Old 2nd Dec 2019, 10:47 pm   #84
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Default Re: RRI T24E Chassis

Hi 1977, posts crossed whilst I was editing my last. As RtoB says it would be a great help and to find the reference number of the 36K resistor mentioned.

John.
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Old 2nd Dec 2019, 10:54 pm   #85
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Default Re: RRI T24E Chassis

Hi,

I'll get to scanning now, as for the 36k resistor, I have replaced it, as Glyn gave me the manual, he marked out where the resistor is for me.

Thanks
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Old 2nd Dec 2019, 11:37 pm   #86
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Default Re: RRI T24E Chassis

I'll have to scan tomorrow evening now - technical issues with the scanner.
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Old 3rd Dec 2019, 4:04 pm   #87
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Default Re: RRI T24E Chassis

In case anyone's wondering, the reason for my question about sound and picture appearing on different frequencies is that the British system "I" has the sound on 6MHz, whereas the Continental system "G" has the sound on 5.5MHz. If the modulator is set for the wrong system, a modern set probably would be able to determine for itself what broadcast standard is in use, and resolve sound and picture without breaking its stride; but an older UK-only set would be expecting to find the sound 500kHz up from where it was actually appearing, so one or the other would always be mistuned.

Anyway, that does not seem to be the problem here. And the modulator is definitely modulating onto UHF, if a UHF set can receive anything out of it .....
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Old 3rd Dec 2019, 6:59 pm   #88
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Default Re: RRI T24E Chassis

Hi,

That's quite interesting to know, actually. Thank you for explaining that as I had wondered about that before, when reading about it.

The manual, I cannot scan it as my scanner has just decided to object to life. I've taken pictures with my phone which will hopefully come through okay, I can take more pictures of specific areas if need be.

Thanks
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Old 3rd Dec 2019, 7:00 pm   #89
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Default Re: RRI T24E Chassis

Additional images:
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Old 3rd Dec 2019, 9:12 pm   #90
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Default Re: RRI T24E Chassis

The schematics in the 3rd and 7th photos are the main ones of interest for the video and sound processing.

3rd photo....the two IC's on the right hand side...the top one is the IF and video detector, the output from that is the composite output from the 5th connection down from the top on the IC's right hand side, it's fed via a coil to the 6Mhz sound carrier filter, the output from that feeds the bottom IC, that IC demodulates the sound and feeds it to the two audio output transistors that can be seen below it.

For the video it's back to that coil, there's another a feed from that coil to a two transistor DC coupled amplifier (to the left of the bottom of the top IC) this amplifier amplifies the composite video signal, the output is taken from the emitter circuit of the second transistor, it then goes three ways...

One to the timebase IC (on the left hand side of the schematic) for sync purposes etc...

One to supply a composite signal to the chroma decoder IC in the schematic in the 7th photo (tagged as comp video at the input to the chroma module)….

And one to the luminance amplifiers, you can see the luminance delay line between the bottom transistor and the next one up in the middle of the schematic in the 3rd photo.

The output from the luminance amplifier is coupled to the emitter circuits of the RGB drive amplifiers on the CRT drive board in the 7th photo (tagged as luminance at the input to the board)

The above isn't meant to be a fault finding guide but just a brief explanation of what signals go where.....so far as I can make out from the photo's.

It might help you to understand what's what in that department.

Any errors in the above then I'm guilty as charged.

Good luck whicheverways.

Lawrence.

Last edited by ms660; 3rd Dec 2019 at 9:20 pm. Reason: word changes
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Old 3rd Dec 2019, 9:38 pm   #91
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Default Re: RRI T24E Chassis

I cannot even make the circuit pictures out Lawrence! as per usual the forum software mangles circuit diagrams in picture formats.

@ 1977 could you convert the photos to Pdf format please and try to re-upload ?
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Old 3rd Dec 2019, 10:19 pm   #92
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Default Re: RRI T24E Chassis

Although it's better than nothing component references are unreadable, as Lawrence says pics 3 and 7 are the most relevant. Would it be possible to link to a flikr account if PDFs are not an option due to your faulty scanner?

Am I seeing things or is the main PSU a simple series regulator instead of a switch mode type. Probably accounts for the reliability but wasteful.

John.

Last edited by jayceebee; 3rd Dec 2019 at 10:30 pm.
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Old 4th Dec 2019, 12:13 am   #93
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Default Re: RRI T24E Chassis

I did wonder how well they’d deal with being compressed.

I’ve uploaded them to Flickr

https://www.flickr.com/photos/185813...57712050094706

Thanks
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Old 4th Dec 2019, 6:27 am   #94
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Default Re: RRI T24E Chassis

That is much better and clearer thanks.
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Old 4th Dec 2019, 1:11 pm   #95
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Default Re: RRI T24E Chassis

Glad it's worked alright.

Hopefully now we can get this TV fixed!

Thanks for your help
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Old 4th Dec 2019, 1:11 pm   #96
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Default Re: RRI T24E Chassis

Have you checked the voltage on the 16.5 volt rail?

Lawrence.
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Old 4th Dec 2019, 1:20 pm   #97
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Default Re: RRI T24E Chassis

No, I'm not actually sure how to test for voltages, and I wouldn't know where either at the moment. (I'm still trying to get to grips with translating circuit diagrams )

Thanks
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Old 4th Dec 2019, 3:25 pm   #98
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Default Re: RRI T24E Chassis

Quote:
Originally Posted by 19Seventy7 View Post
No, I'm not actually sure how to test for voltages, and I wouldn't know where either at the moment. (I'm still trying to get to grips with translating circuit diagrams )

Thanks
The collector of TR202 would be a convenient place to check the 16.5 volt rail.

I'll try and talk you through the signal route(s) later if that's any help for understanding some of the functions in the TV.

Lawrence.
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Old 4th Dec 2019, 6:29 pm   #99
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Brief description as mentioned earlier, all pertaining to the photo's on Flickr..

Ok, let's start with the antenna input/ext. modulator input....Photo 9....Tuner and Interface board...

Input is self explanatory in that schematic, the tuner is at the top right, the other inputs to the tuner are power supply (12v nominal) tuning voltage (variable) and the AGC voltage (Automatic Gain Control) the output is at Pin 7, it's the IF output (the Intermediate Frequency) to keep it simple there are two Intermediate Frequencies, one that carries the sound information and one that carries the vision information, their frequencies are 33.5MHz and 39.5 MHz respectively, you should note that these two frequencies are 6MHz apart, this will crop up later in the description, it might also be worth noting that the sound carrier is Frequency Modulated (FM) and the vision carrier is Amplitude Modulated (AM) when it leaves the transmitter and that info and modulation regime is maintained during the frequency conversion process that's performed in the tuner, ie: the sound IF (33.5MHz) will be Frequency Modulated (FM) and the vision IF (39.MHz) will be amplitude Modulated (AM) so now in effect we have a sound carrier of 33.5 MHZ and a vision carrier of 39.5MHz coming from the tuner.

That's basically it for the tuner so far as the signal goes, next is the IF amplifier, the first stages are still on that board and consist of the circuit pertaining to transistors TR32 and TR33, the output from the tuner is fed to the base of TR32 via a band pass filter, what's a band pass filter? simple, a filter that lets a bunch of desired frequencies through while at the same time telling those that aren't wanted to shove off, bit like a doorman bouncer...The signal output from TR32's collector is fed to the base of TR33, the output from TR33 is taken from its emitter…..that's about it for that IF amplification stage.....33.5Mhz and 39.5MHz IF's in...33.5Mhz and 39.5MHz IF's out (but amplified) that point can be seen on the schematic, tagged as I.F. Output.

So far so good, next part of the schematic to look at is that contained in photo 5....

IF output from the previous board/stage is connected to P501 on the main board in photo 5, you can see that it feeds into another IF amplifier stage, TR161, the output from that are still the IF frequencies which are then fed from its collector to another filter, SWF101, that filter is what is known as a Surface Acoustic Wave Filter or SAW filter to those in the trade, basically it's a filter come shaper for shaping the IF response prior to demodulation, the output from the filter is then fed to the input of the vision demodulator IC, IC101, this IC has several outputs, one for the AFC voltage that corrects the tuning voltage for any small scale tuning drift, one for the AGC voltage for the first IF and tuner stages and one for the demodulated output from the vision demodulator, this latter output is the one that's of interest so far as the signal path goes, it's a composite video signal and contains all the video/colour/sync info and also the sound information in the form of a modulated inter-carrier sound frequency, remember the 6MHz mentioned earlier on? well this is it, a product of the demodulation process in the IC is that the Sound (33.5MHz) and Vision (39.5MHz) carriers are mixed together producing a lower frequency of 6Mhz (the difference frequency) this frequency still contains the sound info in the form of FM which will be separately demodulated. So to re cap signal wise...Sound and vision IF in...Demodulated vision out (composite video) and 6MHz intercarrier sound out....that's basically it for that stage.

Next we follow the sound and video along their two different paths...

Both the composite video and the inter-carrier sound signals output at pin 12 of IC101, let's follow the sound signal route first as that's relatively short and simple...The inter-carrier sound signal (6MHz) leaves pin 12 and connects to a 6MHz filter via coil L102, the output from the filter is fed into the sound demodulator IC601, the output from the sound demodulator (the audio signal) is at pin 13 of IC601 from there it's fed to a two transistor audio output stage (TR603 and T604) and from there to the loudspeaker.....That's about it for the sound.

Next is the composite video signal, also taken from the same output point as the sound signal, you can see that it's connected to the input of a 6MHz trap, TRF2406, the trap's there to prevent the 6MHz inter-carrier sound signal from getting into the video amplifier stages that follow on from it, the first video amp stage after the 6MHz trap comprises the circuit pertaining to TR210 and TR202, the output is taken from the emitter of TR202, from there it splits three ways....

One to the sync separator contained in IC301 via R301 etc and from the same line to pin 8 of P650 which feeds the composite video signal to the chroma module (colour signal processing) shown in photo 1, the third is from the same point as the others but via R207 and an unidentifiable resistor then by way of the chroma trap and via C204 to the base of the third video amplifier TR203, the output of which is coupled to the base of the fourth video amplifier TR204, from TR204's emitter the signal is coupled to the base of the fifth video amplifier TR205 via the luminance delay line, the output from TR205's collector is connected via P520 (this must be plugged in for a picture) to the luminance input (connection 8) on the CRT Drive Board (photo 1) we'll come back to that signal at that point in a bit.

Next is the composite video feed to the chroma module it comes in on pin 8 of P650 (already mentioned before) and the demodulated colour signal outputs R-Y, G-Y and B-Y are fed to the CRT Drive Board (photo 1) via P550, those three colour signal outputs are connected to the respective bases of the RGB drive transistors while at the same time the luminance signal feeds into all three of the emitter circuits of the RGB drive transistors, the combinations of which are fed to the three cathodes in the CRT, there's a lot that actually goes on in the chroma processing but too much to go into given the context of this post...but basically line sync and line pulse in and composite video in....R-Y, G-Y and B-Y colour signals out.

Hope that helps a little bit.

Lawrence.
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Old 4th Dec 2019, 11:48 pm   #100
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Default Re: RRI T24E Chassis

Thank you so much for explaining that! I really appreciate your help!

It'll take a few more re-reads for it to sink in haha.

I really do appreciate you explaining it.

I'm certain it will help me out.

Thanks
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