Adventures with BPC TV set

[wa2ise]

Have an old "Aiwa" TV-VCR combo where the VCR part failed some years ago. The TV part worked as a color monitor and I decided to install a DTV converter box in it, where the VCR part once resided. Seems straight forward enough but just before or after I pull the back off, something decided to fail in the monitor. The off line switching power supply was squealing, and the control line (from the VCR part) no longer had any effect, nor the 5V standby supply was there. Seemed the supply was acting as it had a short on an output. Okay, check rectifier diodes. In circuit they all seemed shorted, so unsolder one end, all but one test okay. Bad one was truely shorted. Power supply became happy with it out. Okay, need a replacement. Need to be careful, as an ordinary 1N4007 diode is fine for 60Hz work, but not for switching power supplies. Well, I pulled a diode from a junked computer CRT monitor, one that did the 150VDC supply like the one I needed to replace. The TV works now, and seems quite happy with the new diode.

Now that I got that out of the way, time to integrate the DTV converter box. The TV has (as mentioned above) a control line that wants about 5VDC applied to turn the TV on. Else it's in sleep mode. Well, the "Digitalstream" DTV box I'm going to use has switched 5VDC that feeds its tuner module. Easy enough to tap that and feed it to the TV control line. Now, the DTV remote also turns the TV on and off with the box. And this converter box can vary the volume of the audio jacks via the remote control, so all I need is an audio amp to drive the TV set's speakers (used to be part of the junked VCR module that is long gone. The TV supply supplies controlled 12VDC which used to power the VCR, but now powers an audio amp.

Tomorrow I'll package this up. Then I'll have a small DTV CRT set.

[wa2ise]

Finally got it all done! These things always takes twice as long as they should. See the picture, a screenshot of a secondary channel on WNBC-DT NYC. You can see the DTV box mounted where the VCR tapes used to go. The box's video output feeds directly to the TV (actually just a baseband NTSC monitor), and the audio feeds an amp from a computer multimedia system (a better grade one) and then the speakers. The box has volume control on the remote, so no control on the set itself.

The box is sticking out a bit, so I can reach the power and channel up/down buttons on the top front right on it.

[MRX37]

Interesting. I just hope it's easy enough to undo if the CRT takes a shit...

[wa2ise]

Originally Posted by MRX37

Interesting. I just hope it's easy enough to undo if the CRT takes a shjt...

It is, The converter box is easily removed and should look no worse for wear (a couple of extra mounting holes underneath, and a few soldered connections on the bottom of the main board, easily undid). It did come out looking a little strange with the box sticking out like that, and sticking out a little crooked in the horizontal plane. And noticed that the image on the CRT is ever so slightly tilted (no, the yoke is firmly attached and dust marks show no movement (and if I did try to twist it the convergence would go to hell, so I left it as is).

As it is, the box's remote is now the TV remote.

An improvement could be had if the box supplied S-video instead of composite NTSC, as I could then feed luma and chroma to the respective decoding circuits in the CRT "chassis" and thus avoid NTSC cross luma defects in the image. But those points are buried inside chips and not accessible.

[andy]

000

[zenith2134]

Wasn't Aiwa a division of Sony at one point?

Does look like a Trinitron CRT with vertically-flat face.

Cool project. I especially like how the converter box's tuner pulse turns the TV on.

[wa2ise]

Originally Posted by andy

Is that a Trinitron CRT?

No, it's an ordinary in line color CRT. Pretty sure it's not, and I think I know what a Trinitron CRT looks like.

Originally Posted by zenith2134

Cool project. I especially like how the converter box's tuner pulse turns the TV on.

Thanks, that's a main feature. Strictly speaking it's not a pulse, but just a voltage level that wakes up the CRT display electronics.

[andy]

000

[Jeffhs]

Originally Posted by zenith2134

Wasn't Aiwa a division of Sony at one point?

It's the other way around, IIRC. Sony acquired Aiwa several years ago.

[Jeffhs]

Originally Posted by wa2ise

Finally got it all done! These things always takes twice as long as they should. See the picture, a screenshot of a secondary channel on WNBC-DT NYC. You can see the DTV box mounted where the VCR tapes used to go. The box's video output feeds directly to the TV (actually just a baseband NTSC monitor), and the audio feeds an amp from a computer multimedia system (a better grade one) and then the speakers. The box has volume control on the remote, so no control on the set itself.

The box is sticking out a bit, so I can reach the power and channel up/down buttons on the top front right on it.

Great job. This is the first time I have ever seen a TV/VCR combo unit converted to DTV, and it looks very good from where I sit. Now, all we have to do is wait for someone here to chime in with a description of how he converted a larger table model or a console in the same way, with the box actually built into the table cabinet or console so it looks like an integral part of the set. Who knows? The idea might catch on.