Color Classic analog board trouble

[YMK]

Meaning, we cannot put a heatsink with 6mm inner diameter on a DO-15 diode that is between 2.60mm and 3.60mm in size.

I thought that might be the case. The spec is very loose so you'll probably have to measure your specific part.

You could always add another in parallel like Apple did. Though they may not share current equally, even a 60/40 split would help.

If the Zener is never forward biased, two parts in series with half the voltage rating would share current equally.

In any case, the single replacement isn't anywhere near hot enough to scorch the board like the originals.

 

[YMK]

You could also buy these and drill them out to the diameter you need:

Amazon.com

 

[JDW]

Gentlemen,

Thank you for your feedback.

I arrived at the office this morning and flipped on the swatch at back. I never booted the machine. The case-back was off, of course, but it can't be helped. There is no air movement in the room in which I am testing the machine. Ambient was almost exactly like last night, right at 30°C. It did not reach 130°C like it did last night, as you can see below. But I think it reached 130°C last night in part because the machine was one for quite some time and more heated overall. Then when the machine is Shutdown, DL22, for whatever reason experiences a temperature RISE.

Note that what I call DL21 in my previous posts is really the same Zener soldered into DL22 pads, not DL21 pads. I should have written DL22 in those earlier images, but I'm not going back to fix them. Please just take note of this minor correction.

I then press the keyboard's power key to boot the machine, and only seconds later it had booted to the Desktop and DL22 had dropped 17.2°C — a rather enormous temperature drop! But that's what I confirmed last night too.

And after waiting 42 minutes for resistor RL22 to heat up, what once was a wicked-hot 170°C component with the tiny stock resistor is now a much cooler-operating 115.7°C. And, if I had the case-back on and fan running, it probably would be cooler than that.

And 43 minutes after booting, Zener diode DL22 had heated up a bit, but still much cooler than in the Shutdown condition:

But only a minute after doing a Shutdown (power SW at back still ON), that dirty rat DL22 was back at a whopping 130.5°C again, just like I reported last night. For reasons I do not understand, immediately after Shutdown is the hottest time for that 5W Zener at DL22. It stays that way a long time (more than a half hour), but it will eventually drop down to the 122°C to 123°C range and stabilize there. But again, that's with the case-back off, and with it on Shutdown, it's probably a tad hotter. It can operate at up to 150°C, but for a margin of safety, we wouldn't want it to go beyond 140°C. And when you consider the stock Zeners were at about 105°C to 110°C (at least, that's what I measured back in 2023), that's about a 20°C temperature increase only because we switched to a single 5W Zener. Better electrically, to be sure, but super hot too (when Shutdown).

And here are the nearby capacitor temperatures (lower today as compared to last night when DL22 was 130°C)...

I am furious at myself for having forgotten to measure Voltage at the cathode of the stock DL21/DL22 zeners prior to my component swap! But I absolutely will NOT remove my current part only to swap in that original part and measure because I would need to do 3 applications of heat to get it back to where it is now, and with the board pads already compromised due to heat, I don't want to do that.

What I can say again is what I said last night. With the 1N5355B 5W 18V (Izt=65mA), I am measuring between 19.1V and 19.3V. That tells me it's getting less than Izt (less than 65mA). The stock parts were 18V 1.25W, Izt=20.8mA 1N5931B. But there were two of them, so you'd need double that Izt and maybe a tad more, so 20.8x2=41.6mA. The circuit may have fed it 50mA or so. But if true, 50mA is less than the 65mA Izt of our replacement, which would explain why I see 19.1 rather than something closer to 18V. In our limited testing, that 1v difference (assuming there is one because again, I never tested the voltage using the stock Zeners) probably doesn't matter much.

But if anyone reading this thread has their Analog Board stock, please hook up your meter as shown below (hooking to that one end of RL62 is easier than hooking to the Zeners), and report your voltage measurement with the power switch on but shutdown...

 

[JDW]

@Kay K.M.Mods very graciously made time today to measure voltage at the side of RL62 that connects to the Cathode side of DL21 and DL22. He had the stock diodes installed. He measured 19.7v. That is a great relief to me because my measurement was about 19.3v when using the 5W replacement Zener. I had been thinking the stock parts might regulate closer to 18V (their Zener voltage) but clearly that is not the case with the stock parts.

I was thinking the only potential issue is the 130.5°C I measured on the new 5W part immediately after doing a Shutdown (power switch still ON). However, both @YMK and @Kay K.M.Mods have pointed out that the stock 2 diodes would have to be on order of 200°C or so in order to scorch the PCB black, so compared to that, 130°C isn't so bad.

The stock parts are 1N5931B, which allows operation up to 200°C (some parts say 175°C). However, the 5W 1N5355B also has a 200°C max temperature spec, but not "continuous." The datasheet suggests its temperature be kept to 150°C or lower.

The good news is that I didn't measure higher than about 130.5°C in my many hours of testing, and the ambient room temperature was about 31°C too. So the only potential for disaster is if you leave your CC plugged into the wall socket and keep the switch at back ON, and leave your machine that way in your room at home during the summer months with the curtains open, so the room temperature rises much higher than normal. Then you may be pushing the upper limits of that 150°C. However, I did find the temperature drops down from 130.5°C to about 124°C after 30 minutes or so.

So after all this analysis, I do think we're good. I can proceed a bit more confidently now with my video creation.

Thanks to everyone for the help and input!

 

[JDW]

And here is the fruit of my labors:

I hope it helps those of you who've been following this thread but haven't yet made the time to try it yet. It's worth it.

A huge shout out to @YMK for having started this thread, and to @This Does Not Compute for chiming in with his experience. Special thanks to @Kay K.M.Mods for having made time to measure voltage for me, and for making extra copies of Doping Mac for sale too! (These are the original books printed in 1997, not photocopies or reproductions.)

 

[JDW]

I was thinking the only potential issue is the 130.5°C I measured on the new 5W part immediately after doing a Shutdown (power switch still ON). However, both @YMK and @Kay K.M.Mods have pointed out that the stock 2 diodes would have to be on order of 200°C or so in order to scorch the PCB black, so compared to that, 130°C isn't so bad.

I'm done filming my video about the 84v mod (13“ High Resolution mod) conversion and will spend the weekend editing. For now, I can say that only some components get hotter than with the standard 68.4V VGA Mod, and those are the components we upgraded to beefier versions in this thread.

The only component that is still somewhat concerning is that Zener Diode DL22 (single diode, 5W) is slightly hotter now in the Shutdown condition AFTER the machine has been booted a while. But if you merely switch on the power switch at back and never boot, DL22 runs a bit cooler.

Zener Diode DL22 TESTS​

Power Switch ON (never booted)​

With VGA Mod (68.4V): 121°C
With 84V Mod: 121°C
Ambient Room Temp.: 30~31°C
NOTE: Rear Housing Removed (case fan not running)

While Booted at least 30 min.​

With VGA Mod (68.4V): 111.8°C
With 84V Mod: 113°C
Ambient Room Temp.: 30~31°C
NOTE: Rear Housing Removed (case fan not running)

Immediately After Shutdown (after having been booted at least 30 min.)​

With VGA Mod (68.4V): 130.5°C
With 84V Mod: 133.9°C (see thermal photo below)
Ambient Room Temp.: 30~31°C
NOTE: Rear Housing Removed (case fan not running)

30 min. After Shutdown (after having been booted at least 30 min.)​

With VGA Mod (68.4V): 123°C
With 84V Mod: 125.2°C
Ambient Room Temp.: 30~31°C
NOTE: Rear Housing Removed (case fan not running)

Resistor RL22, after booted >30 min.​

(Before Beefy 5W Component Swap: 170°C)
With VGA Mod (68.4V): 115.7°C
With 84V Mod: 131.4°C (see thermal photo below)
Ambient Room Temp.: 30~31°C
NOTE: Rear Housing Removed (case fan not running)

 

[BobDaAggie]

I am waiting with baited breath for your video @JDW

I have greatly enjoyed all of your videos so far. I have recently acquired a CC and the main motherboard has been recapped it still does not boot. I am looking forward for your video so I can recap the analog board and then do the 84v conversion

 

[JDW]

@BobDaAggie
Thank you! I'm actually doing my final edits on that video right now!

It will go out to my channel supports first, and then it will be Publicly released.

I've actually never done a recapping video on the Analog Board because when I got my CC, that was already recapped. But @Branchus has an excellent video on the recapping of both the stock CC motherboard and the Analog Board:

- YouTube

Enjoy the videos and music that you love, upload original content and share it all with friends, family and the world on YouTube.

www.youtube.com

I will later do a video about recapping the LC520 board (and probably the stock CC board too, since I have that), and I plan to do the resistor mod on on the 520 board too, which should boost the clock speed from 25MHz to 33MHz. That is really the motherboard I would recommend to you if you won't be getting an LC575 board. Both boards are probably challenging to find, but the 575 is a bit more highly sought after. The LC520 basically becomes a 550 after the resistor mod, and the 550 board is what a CCII uses. I show the 520 board running at 25MHz in my forthcoming video on the 84v mod. The stock CC board is slow and limited to 10MB of RAM, and the bus speed is tied to 16MHz too, making it OK to use for a while, but you'll probably soon be wanting more.

Anyway, the video will come soon!

 

[BobDaAggie]

So when I got my CC the seller also had an untested CC2 motherboard. So I have both. I want to get it running with the known good board before I start messing with the untested board.

I am looking for an LC575 board but that is more of a down the road acquisition.

 

[JDW]

I'm still concerned about the 133.9°C max. temperature I measured on the 1N5355B 18V 5W Zener diode (DO-15 package size) soldered to DL22 pads. It stays that way for about a half hour after you do a Shutdown from the booted condition and then it remains at about 121°C to 125°C (well, at least that is true with the rear housing removed, and with a 31°C ambient room temp.) That was measured using a quality thermal camera, measuring the BODY of the diode, which means the actual junction temperature is 2-3°C hotter.

In my beefy component upgrade, I raised components up and off the board for better cooling. That absolutely will help the resistors, but I've been reading datasheets the last few days and it seems raising that Zener up and off the board may NOT prove best for better cooling. Here's why...

The component is mean to be cooled through its two legs when soldered into 8.0mm² copper pads (a substantial amount of copper which we do NOT have on the solder side of the CC Analog Board), and thermal resistance increases as the Lead Length gets longer, as shown here (straight from the 1N5355B datasheet):

Tthe DO-15 package size is small at 7.60mm long and 3.6mm in diameter...

The DO-15 component body is plastic (well, flame-retardant epoxy, to be precise), which has an approximate thermal conductivity of between 0.8 to 3 W/mK, which is at least a hundred times less than the thermal conductivity of copper. Which is why trying to mount a heatsink to the body of the Zener would be rather fruitless.

Thermal resistance increases with Lead Length because the leads are so small they cannot act as effective heatsinks alone. They are merely channeling that heat away from the component body to whatever copper you have on your PCB. In the case of the CC Analog Board, it's not much and certainly no where close to the 8.0mm² suggested by the Zener's datasheet.

I mentioned in the closing segment of my Part 2 (84V mod) video that I was thinking about using 100% copper alligator clips, but I didn't want the clamping force to harm the component's body. But as I later found out and just mentioned, clamping it to the plastic body wouldn't be effective.

So now I am thinking it may be best to SOLDER at least one copper alligator clip to ONE of the LEGS to reduce the temperature of the Zener.

I've not done anything yet. I'm just thinking out loud. Sure, my advice of switching off the machine after use helps alleviate the problem, but what about people who forget to do that? That's the heart of my concern.

I'm not sure if older but physically larger 18V 5W Zeners would help dissipate heat better. Probably not. They might need a heatsink on at least one leg as well. But their DO-201 package size is much larger than DO-15, at more than 9mm long and 5mm in diameter, as you can see here:

NTE5133A, 18V @ 5W Zener Diode 5% ~ DO-201 Axial (ECG5133A) | eBay

NTE NTE5133A, 18V @ 5W Zener Diode 5% ~ DO-201 Axial Lead Case (ECG5133A). Replaces ECG5133A. Case Size: DO-201. Polarity: Color Band Denotes Cathode.

www.ebay.com

Cheap for people in the USA, but expensive for me, as shipping alone costs $18.66. For one silly diode! Crazy!

Alternative vendors of those new old-stock parts:

https://www.tme.com/jp/en/details/nte5133a/tht-zener-diodes/nte-electronics/

NTE5133A, 18V @ 5W Zener Diode 5% ~ DO-201 Axial (ECG5133A)

NTE NTE5133A, 18V @ 5W Zener Diode 5% ~ DO-201 Axial Lead Case (ECG5133A) Specifications: Voltage: 18 Volts Wattage: 5 Watts Tolerance: 5% Polarity: Color Band Denotes Cathode Case Size: DO-201 Replaces ECG5133A

marvac.com

 

[JDW]

Can't believe it. Just got home from work and was able to test my Mystic when I realized that I forgot to flip off the power SW at back last night. The power was on all day in my room at home with no A/C in the heat of summer, and that means the ambient room temperature was probably 35°C or even higher.

Even I can't remember to flip the silly thing off!

So this just serves as a prime example of what my previous post really means. We need to cool that 5W diode because we must account for human error and the tendency to leave the machine switched ON by accident.

 

[Paolo B]

Can't believe it. Just got home from work and was able to test my Mystic when I realized that I forgot to flip off the power SW at back last night. The power was on all day in my room at home with no A/C in the heat of summer, and that means the ambient room temperature was probably 35°C or even higher.

Even I can't remember to flip the silly thing off!

So this just serves as a prime example of what my previous post really means. We need to cool that 5W diode because we must account for human error and the tendency to leave the machine switched ON by accident.

By chance, the same here. Unintentionally left the power cord connected to my Mystic and the power switch on. Back from holidays, the bloody thing was very warm to the touch…

 

[JDW]

Mine was especially warm on the right side, due to the hot degaussing component there. But even though I couldn’t feel the same level of heat on the left side, I can only imagine how hot that DL22 diode was getting.

 

[JDW]

After my 84V mod (640x480), the heat of the 18V 5W Zener used at DL22 caused me a lot of lost sleep. I just wasn't satisfied with the heat it put off. After some in-depth study, it seems the way these Zeners keep cool is to dump all their heat into the legs, which is why the two stock Zeners where mounted right against the board, rather than being stood up on their legs. The higher you raise these Zeners, the worse the heat dissipation becomes, UNLESS one or both legs in soldered into a heatsink. If you look at the SE or SE/30 Analog Board and examine the side of the Flyback cage facing the bipolar capacitor, you will see one diode has a leg soldered to the metal cage for heat sinking reasons.

When I made my BEEFY UPGRADE video, I didn't want to use my 100% copper alligator clips (affiliate link) for fear they might fall off and cause a short. But after much thought, I decided to cut the alligator clips in half and solder one of the halves to either side of the Zener. Not only that, but I bought a physically larger DO-201 package size Zener diode with the same 1N5355B part number:

• MOUSER: https://www.mouser.com/ProductDetail/637-1N5355B
• DIGIKEY: https://www.digikey.com/en/products/detail/diotec-semiconductor/1N5355B/22189670

The legs on that DO-201 edition Zener are thicker than the smaller DO-15 5W Zener I had been using, and the thicker legs are why I've not updated my Mouser cart to use that DO-201 version instead. I don't think most people would be willing to do the work I did to install it. But I want to write this report for those of you who do wish to follow my lead in the quest for a much cooler running 18V Zener on your CC Analog Board. As such, I recommend most people add the DO-201 diode above to their preferred Cart below, and that way you can decide which 18V Zener you want to use (going with the DO-201 if you don't mind hand-drilling the DL-22 pad-holes to widen them).

• Mouser Cart: https://bit.ly/4oaw9nU
• DigiKey Cart: https://www.digikey.com/short/d8m2zfdq

Basically, the legs of the physically larger Zener won't fit the DL21 or DL22 pad holes. The legs will fit through the nearby air vent holes, showing that the DL22 pad holes need to be made only a little larger. So I took my little hand-drill (affiliate link) that came with my Hakko FR-301 Desoldering Gun kit to slowly a carefully widen the pad-holes at DL22. And this is possible because the board is only 2-sided (not multi-layered).

I had a pack of tiny drill bits (affiliate link) ranging from 1.0 to 1.5mm in size, and I went up in size, one by one, to slowly widen the DL22 pad holes. I twister very slowly such that no copper was lifted by accident at all. Ultimately, I was able to make the holes wide enough for the larger DO-201 Zener legs to fit through.

After that, I used some nippers to cut off the cap holding the Aligator Clip center bar in place, which holds the top and bottom of the copper alligator clip sides together. That wasn't too hard with hand nippers because the copper is a lot software than other metals like stainless steel. To make it easier, you can even cut up the shorter half of the clip before you cut off that center-bar-cap.



That allowed me to use the longer side of the clip which has the crimp-feet, which I used to hold the clip securely around the legs. And there is a HOLE in that side of the alligator clip which I used nearest the body of the diode. I used my hot air station set to 365°C and a soldering iron set to 350°C with a fat 4mm wide tip (larger tip sizes allow more heat to be applied) to first put a little solder around that hole to make it easier to solder to each Zener diode leg. When I did the soldering, I tried to keep the heating time as short as possible so as not to damage the diode. I used Helping Hands to hold it during my soldering, and I used a couple aluminum heatsink clips to draw as much of my soldering heat as possible away from the diode (not sure if that helped in light of the close proximaty of my solder application point to the diode body).

I also used needle-nosed pliers to bend-put the middle part where the center bar once held the clip together, and those stick out like little half-circles with holes in the middle.

The result is shown in my photos below.





You can see how much larger the DO-201 package size is compared to the 5W Zener I was using before...



It's larger in length and in width.

It fits into DL22 pads like this...



Not wanting anything to short against the nearby metal cage, I applied some rubbery epoxy to a location that won't prevent the lid of that cage from being removed...



But I later realized that epoxy was totally unnecessary because the cage is Ground, and the Anode side of the 18V Zener (which comes very close to the cage) is also Ground! So even if the Anode side Heatsink was to touch the metal cage, it wouldn't be a problem.

Before I soldered the Zener, I scraped away a good amount of the solder mask so I could apply a larger clump of solder. I covered the unused DL21 pads with the solder too. Most of the heat should flow into the two copper clip-halves I attached to the Zener's legs, but any remaining heat would then be sunk into the large amount of solder on the solder side of the board, which you can see here...



Here are more photos after it was soldered...



I replaced the nearby capacitor, because the person who had recapped that Analog Board in the past (before I received the machine) used a silly 85°C rated cap there, which is a huge no-no in that super hot area. All caps should be rated 105°C or higher! Also, the cap that was used there had the wrong Lead Spacing and was stood up on its legs with no hot glue — another huge error on the part of whoever recapped the board. So I bought a cap with the correct lead spacing which allows the cap's base to sit flush with the board.

After that install was done, I then did Voltage Testing. With my previous (physically smaller) 5W Zener, I measured 19.3V, which was higher than it should have been because the Zener is "5% tolerance" and therefore should regulate up to a maximum of 18.9V. Maybe the diode is getting too hot and that is why the actual regulation was 19.3V? Possible. But look at what I get now with the DO-201 diode (with my copper heatsinks) while the Back Side Power Switch ON and the Mac BOOTED...

18.4V! Yeah!



I then Shutdown the Mac, which increases the voltage slightly, but even then I was only getting slightly higher voltage...

18.5V! Great! Nicely below the 18.9V max voltage this 5% tolerance Zener should regulate to.



Having the expected voltage of about 18.4V~18.5V was so nice to see!

I then started taking Thermal Measurements, noting that my ambient room temperature was 29°C, which is about the same as the room temperature of my previous thermal measurements.

5 Min. after switching on the back side Power Switch (not booted):

17 Min. after switching on the back side Power Switch (not booted):

Immediately after Booting (which drops the voltage and therefore drops the Zener temps)...

Don't forget, this is with the rear housing removed and no fan running while booted.

33 Min. after booting... (Running the Daystar Power Demo the whole time, with the LC575 motherboard’s CPU clocked at the stock 33MHz)

Soon after SHUTDOWN (voltage rises so temps rise)...

The maximum temperature I measured, which was only a minute later...

Compare that 114°C to the 133.9°C I measured with the smaller 5W Zener soon after shutdown. The larger DO-201 diode, in combination with my two hand-crafted copper heatsinks, is about 20°C cooler in terms of the maximum temperature measured soon after Shutdown.

25 Min. after Shutdown, the Zener had cooled a bit to just under 106°C. With the smaller Zener, I the temps at that point in time had dropped to only 125.2°C. So the larger Zener with heatsinks is still a very nice 19.2°C cooler at this point.

When I measured the outside part of one of the Alligator clips, toward the top, it measured 75°C, which is much cooler than the body of the Zener. Note that I used only solder to secure the clips to each diode leg. I didn't try to add any thermal glue at the part where the clip meets the body. Thermal glue may or may not draw a bit more heat from the body into each clip.

Overall, I am extremely pleased with this result and recommend it to anyone who doesn't mind a little hand-drilling to widen the pad holes at DL22. It's not hard with the right tool, and if you take it slow, it won't damage anything. You need about 1 hour to do all the work I did. And when you consider that the hottest temps are reduced by about 20°C, it's a meaningful difference. Not sure if the reduced temperatures are what led to the more accurate voltage regulation, but 18.4V is better than the 19.1V I got with the smaller and hotter Zener.

With this setup in place, I am less concerned about heat damage when the machine is accidentally left switched ON at back. Still a good idea to keep it switched OFF to save energy, but the physically larger DO-201 Zener diode with copper heat-sinks should result in longer diode life.