First time attempting CRT service - Conrac Industrial Monitor

[vintage.digi]

Hello! I hope this is the right thread. I didn't see one specifically about service.

So, I just picked up this industrial Conrac monitor from the 80s. I realize that's a really odd monitor for a collector to want. I like unique stuff, I want to have a little bit of everything, and this brand has become very intriguing to me lately. I'd love to have one of those proper Conrac production monitors with RGB eventually, but I'd also like to have this industrial unit working as well.

I will take some more pictures the next time that I'm at the office. You can see it here as long as this eBay listing is still up:

https://www.ebay.com/itm/CONRAC-CRT-...72.m2749.l2649

BTW, I didn't pay near what that asking price shows. I sent an offer I didn't think they'd be likely to accept because shipping costs would have taken most of it, but they accepted and now it's here. Bad news is that I haven't got it to work yet. I have not tried to service a CRT but I have wanted to learn how for a long time. I figure that it's either the perfect unit to start out on, or the worst one, or somewhere in between.

So here's what I've seen so far. The board with the tube socket was disconnected from the back of the CRT when it arrived. I figured this just fell out during shipping, no big deal. Lightly bent the pins back into place with my fingers, (they can bend WAY easier than I expected) and reattached the board.

I powered it up, and I hear the power running through the machine and saw an internal LED come on. Nothing happens on the screen though, and I don't feel any static. I can see an orange glowing in the back of the tube. Pressing the degauss button does produce a nice loud "bong" sound. I've tried every button on the face of the panel. I've also tried connecting an RGB signal into the back.

At some point, I heard an extremely high-pitched whine come out of the unit, which I was probably almost too old to hear. I believe this was during the time that I had a signal connected. The sound worried me and I didn't want to try and reproduce it since I didn't know if it could damage the unit.

So, I think my next step in progression is going to be to get some more information. There's a label on the tube that I can't see without removing the tube.

As a side note, my mom still occasionally brings up how I used to want to bring broken TVs home when I was a small kid. I used to always say, "I know I can fix it!" I'm probably lucky that she didn't let me try, but now I think it's time to actually make that childhood dream come true.

[zeno]

Since the CRT PCB fell off it took a good hit. If you follow the input
cable it usually plugs into the CRT board. Make sure it isnt loose.
After that there is a good chance there is a cracked PCB. You
may want to start a claim just in case ........

Note: On most monitors if it dosnt see a sync signal it will go into
standby mode to save electricity. The sync comes in the cable then over to the main board.

good luck
Zeno
LFOD !

[WISCOJIM]

Originally Posted by vintage.digi

BTW, I didn't pay near what that asking price shows. I sent an offer I didn't think they'd be likely to accept because shipping costs would have taken most of it, but they accepted and now it's here.

That was a good discount!

[JohnCT]

Originally Posted by vintage.digi

I can see an orange glowing in the back of the tube.

Most consumer grade CRT displays use a secondary winding off the flyback to produce filament. If the filament was lit, there was at least high voltage. Some later high end units used a separate high voltage transformer and horiz output transformer instead of a flyback, and sourced the tube filament elsewhere. I suspect the Conrac uses something more advanced than a flyback to provide horiz scan, HV, and filament. This monitor may use a DC filament sourced from the power supply or even its own dedicated source.

Do you have a schematic for this unit?

Originally Posted by vintage.digi

At some point, I heard an extremely high-pitched whine come out of the unit, which I was probably almost too old to hear.

As we get older, our audio response drops considerably below 15Khz, and many units used double that rate. In addition, most switch mode supplies run over 30K, so we don't hear them like we did.

So, I suspect if you heard a high pitched whine, it could have been a load on the power supply or sweep. Since these circuits are current monitored and lower the frequency to reduce current, a load will often manifest itself as a squeal that's dropped into our hearing range.

Quick checks are to look at any high power transistors for shorts from Collector to Emitter. These transistors can be the metal TO-3 or big plastic transistors mounted on heatsinks. Any shorted transistor will shut the power supply down.

John

[vintage.digi]

Well, I just stopped by the office for a couple minutes and snapped some photos while I was there. I found one thing that needs to be fixed before I try again; a broken wire.

This is from yesterday when I unpacked it before reattaching the board: https://imgur.com/tH0DubI

Here's that board now: https://imgur.com/UHRPjyv

Here's the board those input wires connect to, on the side: https://imgur.com/GKsTt25

Another internal board: https://imgur.com/uwk6Q5d

Here's the best I can see of the side of the tube. Enough to know it's a Matsushita: https://imgur.com/l6VHFAH

And here's the broken wire, which if I'm really lucky could be the source of the problems: https://imgur.com/jglpBSc

Originally Posted by WISCOJIM

That was a good discount!

How did you get it to show what I paid? I thought I knew a lot about using eBay but it doesn't show that for me on other peoples' purchases.

Originally Posted by JohnCT

Do you have a schematic for this unit?

I don't have a schematic yet. I tried searching Conrac's site on the Wayback Machine but I didn't find any manuals. There's one on eBay but $22 for the manual plus $22 shipping seems high.

[WISCOJIM]

Originally Posted by vintage.digi

How did you get it to show what I paid? I thought I knew a lot about using eBay but it doesn't show that for me on other peoples' purchases.

A site called Watchcount.

http://www.watchcount.com/ebay-best-...sold-price.php

.

[zeno]

The e-bay link you posted went to a 17" Sony monitor NOT a Conrac so
what I said may not apply in your case. Anyhows that monitor
is really built ! Much better than any consumer TV that wasnt
hand wired. Its obviously US or Ca built not at all Sony.

73 Zeno
LFOD !

[WISCOJIM]

Originally Posted by zeno

The e-bay link you posted went to a 17" Sony monitor NOT a Conrac so
what I said may not apply in your case. Anyhows that monitor
is really built ! Much better than any consumer TV that wasnt
hand wired. Its obviously US or Ca built not at all Sony.

73 Zeno
LFOD !

[vintage.digi]

Originally Posted by zeno

The e-bay link you posted went to a 17" Sony monitor NOT a Conrac

A few years ago, in all of their wisdom, eBay added a "feature" that makes it so that when you try to look at a sold item, it automatically takes you to something they want you to buy now. I sell on eBay for a living and buy lots of things on eBay and have found this feature useful a total of... never!

This was also around the same time that they started automatically picking categories for your search so that it will hide items that you would have bought if you knew they were there. It can also make it harder for buyers to find what you're selling if eBay mistakenly picks the wrong category for a given search. This has happened to me and I lost a lot of sales on a popular product because of it. I had to go and buy out my competitor who had his product listed in the wrong category, just to get the more specific category back to being the suggested one. Yay, eBay!