Broken inductance analogue board Mac Plus

[Tony359]

Hi all,

I'm restoring a Mac plus and while inspecting the analogue board I found the below inductance with a broken core.

I'll test this unit once I've removed the RIFA and replaced some leaky caps, I am told the picture was a bit wobbly?

Question: do you think it definitely needs a replacement or it could work as is? And if a replacement is needed, is there a way to source a new one or it has to be one from a donor board?

Cheers!

Edit: To be clear and respectful towards this community, this is a paid service I am offering to someone. I lost my 9-5 job some time ago and this is something I am dipping my toes in alongside with other things.

 

[Callan]

As long as the inductors wires havent been broken at the base, there is continuity through the wires and the circuit is Complete, and (fiainally) the core imside the windings are intact I would think it would be fine. I would secure the two broken pieces to prevent and further damage. To verify you could pull it from the cicuit and test it with an lcr meter.

 

[Tony359]

Thank you Callan,

So you're saying that what is outside of the winding does not count for the intended inductance? I can try to measure it - good idea - but I don't have a reference value to compare it with.

Indeed I was thinking of gluing the two pieces and then add some hot glue to the outside to try to keep them in place in the future.

 

[Callan]

(Edited : i re-read your reply to me and realized i misunderstood what you were asking. To answer that... yes. The ferrite core on the base will effect the inductors field (hence its inductance), but to what effect i'm not sure. As long as the internal core is intact i believe it won't be much and if you just put the 2 pieces back together i believe it will be negligible. I'm not an expert on inductors, but i've fixed enough monitors to say it say its normally fine if you do that). The outside winding is the inductor. ((The core helps increase the inductance). I'm saying as long as the ferrite core is still inside the winding and the wire still has continuity through it from solder pad to solder pad (i.e. test solder side of the board to confirm) It'll still work. Leaning tower of piza won't effect it (unless they were using that parts field to effect another part - which I don't think it is). If it's broken part of the ferrite core at the base it will effect the current some, but if those 2 first facts are true you can plug it in and try it. That's the linearity coil (L3 on scematics). You'll see if its still viable by looking at the picture, but you have to verify whatever knock it took didn't isolate the inductor from the circuit (ie break the windings from the solder pad). I'd just straighten it out, confirm the inductor has continuity from its solder pads (remeber it's just one piece of wire, so as the say it should 'ohm' out), and I'd test it. worst case is you'd see distorted linearity on the monitor, best case it works fine.

 

[Callan]

For reference : Looking at the scematics you can see it ar the bottom of the scematic to the left of the horizontal coil. R1 is parallel with l3 (your inductor)

 

[Tony359]

Thanks again, I understand. I will check that there is no further damage and try to measure the inductance for future reference. Thanks for looking into the schematics for me, it's nice to know what that is for, so I can check if it has any effect.

I'll make a repair video of this Plus, I'll share it when it's done - thanks for now!

 

[Tony359]

Update.

I measured the inductance and it read 0.3Ohm, 0.01mH. With or without the broken part (which I could slide out easily).

I glued the two parts with epoxy, left it overnight in a clamp.

The following morning I tested the inductor again and it now reads as a resistor, 0.24 Ohm. Yes, the glue might have acted as insulator between the two parts but I did test it with just the top part and it was still reading as an inductor.

My component tester is the cheapo from Ebay (one of the many clones) and that might be the issue. It's weird though.

I do have a picture, I still need to check properly. For now I see the picture is a bit trapezoidal, not sure if that would be the consequence of that.

But for me the good news is that all is good, the analogue board I re-capped is happy, voltages are happy, I can boot into the OS and the picture looks sharp and stable - though a bit dim, it might be a tired CRT or might need a little drive adjustment.

Thanks for your help so far!

 

[Callan]

Your Welcome! Snooper 2.0 is has a bunch of test patterns you can use to check your monitor out. I'm not sure of it runs on a Mac plus, but if not maybe someone can chime in and suggest an alternative.

Congrats on your repair!

 

[Tony359]

Thank you! So far so good, I really don't see issues with the CRT. I caught it jumping once, I since cleaned the pots on the analogue board. Today I've tinkered with the Yoke and the magnets and all the adjustments and I'm happy with it!

Thanks for the idea about Snooper 2.0 - I was wondering if there was something with test patterns, always useful!

 

[Callan]

Sometimes your anode cap won't seal 100% and you'll get a 'pop' or jump. This can happen when the tube is a little dirty around the anode cap. I clean the area around / unde the cap and normally put some molykote (silicon grease) on the cap to help seal it to the tube. That should prevent any future discharges.

 

[Tony359]

I hadn't cleaned that yet so good point. The Tube is now spick and span and yes, I've added some dielectric grease under the suction cup indeed - It seals it and makes it glide on the glass which facilitates removal if needed.

What I saw though (only once) didn't feel like HV glitch - the bottom of the picture jumped for a moment. A glitch in HV would've slightly collapsed the whole raster, am I right?

Anyways, I ran the Plus today for an hour or so, all really seems to be working totally fine - fingers crossed!

Adding a pic of the patient - before CRT was adjusted

 

[Callan]

Ahhh... When you said it jumped once that would be the normal reason for that.
Yeah... you'd know if it was high voltage related. You'd hear it and the screen kinda twerks (jumps, squiggles, etc). I wouldnt think it would collapse unless whatever caused it affected the b+ in which case yes it would (or bloom depending on how the b+ was effected).

If you've burn't it in for an hour with no problems I think your good to go.
It looks good!

 

[Tony359]

As promised, here is the video repair! Comments are very welcome! I mentioned Tinkerdifferent in the video and linked these pages in the description. Thanks again for your help!

 

[Callan]

Enjoyed the video! Great job on the restore! I was already subbed, but definetly liked it. Looking forward to the next.

 

[Tony359]

Thank you! Next one is still in the making, the caps on the Color Classic AB decided to have a leak so I'm still mopping! So many unknowns, I have no idea whether the LB or even the CRT works on that machine.