Help Identifying Burnt Resistor On Color Classic Analog Board

[red_leader]

I have the typical burning resistor and pair of diodes on my Color Classic analog board (photo of problem area provided, with resistor and diodes circled in red). 2 of them, actually, same exact issue. They both work, but I'd rather not push my luck and fix them while I can.

Can someone please provide me with the values of the resistor, and any compatible variants if they exist? Also, do I need to replace the two diodes nearby, or does replacing the resistor fix that problem too?

Thanks in advance for any assistance, and for your time.

 

[retr01]

Hi @red_leader!

Are you familiar with identifying the bands on the Zener diodes? You can refer to charts for three, four, five, and six band diodes that identify the colors, values, and tolerances. That can help you to determine which ones to replace.

I have seen posts elsewhere, such as on 68kmla, about those diodes scorching on the color classic analog board, which is a common issue due to age and heat. However, no one is saying specifically what replacement diodes are. That baffles me.

Your picture does not provide enough light to see the bands of the burnt diodes. Can you please take another picture with more light?

I found a nice resource, a resistor calculator online that can help you to figure out by selecting the number of bands and the colors. Here are the charts for the three, four, five, and six banded diodes.

 

[retr01]

And here is what this online resistor calculator looks like:

 

[retr01]

@red_leader, I checked a post on the 68kmla again, and I see that someone found the diodes' values on the Color Classic analog board that scorched, like yours.

I gathered the following information:

• DL21 22 diodes and RL62 (47 Ohms)
• RF11 (390 Ohms) resistors
• CF8 cap replaced with a 3300uF 25V 105C

Help with a Macintosh Color Classic analog board

Hi everyone! My first post here (I think...)! My name is Marco, a vintage computer enthusiast. I have a collection of old Macs, Amigas, Ataris, MSX and such... simply love them! I spend a lot of time restoring them to bring them back to their glory days... now, I am strugling to bring back a Mac...

68kmla.org

 

[red_leader]

@retr01 My RL62 is alright for now, not really nearly as toasty, and I was told the Zener diodes are 1N59 when an awesome Youtuber named Bruce of Branchus Creations took a quick look at his analog board after working on a Color Classic logic board. The photo I posted, on the other hand, is a photo of an analog board that I found online and, believe it or not, is a lot clearer than the ones on my board (they're a lot darker due to burning).

I guess I need a pair of those, along with a 390 Ohm resistor.

My Color Classic does still work as it is, and the logic board is already recapped, so this is preventative maintenance. I suppose I should also replace all of the caps, especially that 3300uf near the problem area, since I was told that that one loves to cause a mess when it dies.

I'll also need to eventually replace the 'Tron, because unfortunately, both the green and blue guns are dying and so the colors are a muddy brown. I don't believe that's a fixable problem. I'd love to be wrong about that, though. Trinitrons are rare, especially good ones from that era.

Thank you for getting back to me. I appreciate the assist.

 

[retr01]

You are welcome, @red_leader. I realized I did not answer the second of your two questions in your first post in this thread. My apologies.

Also, do I need to replace the two diodes nearby, or does replacing the resistor fix that problem too?

That would be a good idea, yes. As you mentioned, you do not want to push your luck, and you are right. One day, those burnt resistors will finally give out and cause issues like making your beloved Color Classic go kaput.

 

[retr01]

My Color Classic does still work as it is, and the logic board is already recapped, so this is preventative maintenance. I suppose I should also replace all of the caps, especially that 3300uf near the problem area, since I was told that that one loves to cause a mess when it dies.

I agree.

I'll also need to eventually replace the 'Tron, because unfortunately, both the green and blue guns are dying and so the colors are a muddy brown. I don't believe that's a fixable problem. I'd love to be wrong about that, though. Trinitrons are rare, especially good ones from that era.

CRTs are built to last a long time. There could be other factors causing the problem that your screen is not producing full colors, such as magnets or other parts needing readjustment. I'd advise you to try to find ways that colors could be corrected so that you can keep the beloved Sony 'Tron monitor in your Color Classic.

 

[red_leader]

I agree.



CRTs are built to last a long time. There could be other factors causing the problem that your screen is not producing full colors, such as magnets or other parts needing readjustment. I'd advise you to try to find ways that colors could be corrected so that you can keep the beloved Sony 'Tron monitor in your Color Classic.

True, CRTs are definitely built like tanks. Just as heavy, too. However, in my experience with all Trinitrons (including TVs), a green tint starts to develop due to the other guns starting to wear out (according to other and multiple sources). That's why I'm suspecting that it's happening to this Trinitron, but at a more advanced stage. However, it goes without saying that if I can find a way to fix what I have so it displays colors accurately, I will absolutely do my best to do so.

 

[retr01]

if I can find a way to fix what I have so it displays colors accurately, I will absolutely do my best to do so.

Let me see what I can find out.

 

[red_leader]

Let me see what I can find out.

Your advice thus far and in advance is quite appreciated. Thank you very much.

 

[retr01]

Hi @red_leader, I have information after consultation with one of the most experienced retired Apple Service Technicians:

Usually the problem is with the CC's video circuitry or a loose connection (or connector) rather than with the CRT itself. Failure of a single gun in a Trinitron is uncommon. The only CRT related CC failure I can recall is with one that had suffered a fall. Not bad enough to break the CRT open, but enough to bend the gun structure from the impact.​

​

I'd recommend a quick check using the Apple Personal Diagnostics software. There's a display check section in it that let's you bring up a set of color bars and some other patterns that can help diagnose the problem.​

That confirms what I suspected. The electron guns in the Sony Trinitron CRTs are actually extremely resilient. It’s the other issues that can cause color issues. Please try those as suggested.

 

[red_leader]

Hi @red_leader, I have information after consultation with one of the most experienced retired Apple Service Technicians:

Usually the problem is with the CC's video circuitry or a loose connection (or connector) rather than with the CRT itself. Failure of a single gun in a Trinitron is uncommon. The only CRT related CC failure I can recall is with one that had suffered a fall. Not bad enough to break the CRT open, but enough to bend the gun structure from the impact.​

​

I'd recommend a quick check using the Apple Personal Diagnostics software. There's a display check section in it that let's you bring up a set of color bars and some other patterns that can help diagnose the problem.​

That confirms what I suspected. The electron guns in the Sony Trinitron CRTs are actually extremely resilient. It’s the other issues that can cause color issues. Please try those as suggested.

I already intend to recap the Color Classic's analog board, but I've run into non-Mac Trinitron displays showing way too much green as they get older, usually with 80s and early 90s TV sets. Some people say it's the guns in the CRT itself, while others say it's the transistors driving the guns. I hope it isn't the latter, because while it's not easy to find a replacement CRT, something tells me it'll be even harder to find obscure Sony transistors for an Apple analog board.

 

[retr01]

obscure Sony transistors for an Apple analog board.

Hmmm. Have I not heard about Sony transistors on an analog board for the CC or CC II?

@Branchus has an awesome overlay photo of the caps for the CC analog board:

Macintosh Colo(u)r Classic Analog Board - Recap-a-Mac

While people are busily recapping their vintage Mac logic boards, they sometimes forget that some analog boards are also prone to capacitor leakage....

recapamac.com.au

 

[red_leader]

Hmmm. Have I not heard about Sony transistors on an analog board for the CC or CC II?

@Branchus has an awesome overlay photo of the caps for the CC analog board:

Macintosh Colo(u)r Classic Analog Board - Recap-a-Mac

While people are busily recapping their vintage Mac logic boards, they sometimes forget that some analog boards are also prone to capacitor leakage....

recapamac.com.au

Bruce is awesome, and I've already identified other necessary components because of him. Thank you for the link to the overlay. There is also another possibility: I don't have a clue what I am talking about, and I am likely wrong whenever I say something I think I know about tech lol.

I will see what I can accomplish, although this might be the last you hear from me for a while. Life is happening and my tech hobbies are going to have to be shelved.

Thanks again for all of your help and knowledge.

 

[retr01]

I understand, @red_leader. You're welcome.