Heathkit IO-4510 Questions and Repair

[SilverTailJay]

Hello everyone! Looks like this'll be my first post on this place, hopefully not the last.

Here's the low-down, I got actually 2 heathkit oscilloscopes a while ago from the trash, from what I can tell the particular one is the older of the two. It dates from around 75, while the other dates from around 1980. I only took pictures of the internals of this one unfortunately.

I was only able to test the older of the two, the newer one is missing it's mains cord, and I will 100% need help identifying what kind of cord I need to buy down the line. The older one did turn on, though, the only thing that came up on the screen was what looked like a very blurry, flipped over, left half of a bell curve. I twisted *ALL* the nobs, and none of them made a difference. Most likely broken.

So today is the day I decided to pop it open and start de-soldering some things. Before that, I have a question as to what the hell these things on the side are. Are these some bigass capacitors? I notice that the metal bits don't actually connect to each-other! This looks very similar to the layers in a ceramic capacitor, just in a much larger and much more low-tech format! (IMG1.jpg)

So, I de-soldered the big cap that you can also see just to the right of the transformer in IMG1.jpg, I also got to remove a resistor in that process as well. It was quite well out of spec, 47k with a 10% tolerance, it was at 63k. More than likely caused by my hamfisted soldering with my fixed heat 40w Weller. (Massacre me) Anyway, i got the big cap out, and using the capacitance tester built into my Fluke 115 I was able to find that pretty much all of the caps in this were off. the two 100uF leads were at 150ish-uF, the 300uF cap was all the way up at 590uF (though, it seems unlikely a cap would GAIN capacitance over time?) so, this will need to be replaced. Suffice to say, googling 25-228 got me diddly squat, so I'll need to find some other replacement option. Any advice on what to replace it with? (cap pictured in IMG2.jpg)

If you have any questions or general advice, please, let me hear it. Hopefully I got this post in the right spot.

Thanks.

[SilverTailJay]

I managed to get all the caps, and resistors off the board. Some of them are going to be quite hard to find. I don't know the composition of the capacitors, and I'm not sure if it matters or not. For the most part, the only caps I was really able to find on Mouser that could replace the 1200 and 3000 volt caps are polypropylene film caps. For example, the best I can seem to do with those 1200VDC .5uF (Yes, there are no units but I've confirmed its in uF) caps is two 600VDC 1uF caps.

Also, this is where my novice in electronics engineering probably shows. One of the resistors I've removed was a 2.2megohm resistor, it was on the 3000v line. Here's the schematic https://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20IO-4510%20oscilloscope%20schematic.pdf
For all I can tell, that resistor was R708. Its right near the top of the schematic, just under the 3000v output. That resistor should have been dissipating 4w of power, but it's absolutely tiny. It seems more like a half a watt resistor, if that. I must be missing something there.

 Also, when looking for replacements, for the ones that aren't clearly labeled 1w or 2w resistors, is 1/2w a good number to shoot for?
I don't know if the resistor composition has anything to do with it, but clearly they managed for a long time on small power dissipation resistors.
I've thrown in a picture of the empty board, just for kicks.

Thanks.

[slbender]

Hello everyone! Looks like this'll be my first post on this place, hopefully not the last.

Here's the low-down, I got actually 2 heathkit oscilloscopes a while ago from the trash, from what I can tell the particular one is the older of the two. It dates from around 75, while the other dates from around 1980. I only took pictures of the internals of this one unfortunately.

I was only able to test the older of the two, the newer one is missing it's mains cord, and I will 100% need help identifying what kind of cord I need to buy down the line. The older one did turn on, though, the only thing that came up on the screen was what looked like a very blurry, flipped over, left half of a bell curve. I twisted *ALL* the nobs, and none of them made a difference. Most likely broken.

So today is the day I decided to pop it open and start de-soldering some things. Before that, I have a question as to what the hell these things on the side are. Are these some bigass capacitors? I notice that the metal bits don't actually connect to each-other! This looks very similar to the layers in a ceramic capacitor, just in a much larger and much more low-tech format! (IMG1.jpg)

So, I de-soldered the big cap that you can also see just to the right of the transformer in IMG1.jpg, I also got to remove a resistor in that process as well. It was quite well out of spec, 47k with a 10% tolerance, it was at 63k. More than likely caused by my hamfisted soldering with my fixed heat 40w Weller. (Massacre me) Anyway, i got the big cap out, and using the capacitance tester built into my Fluke 115 I was able to find that pretty much all of the caps in this were off. the two 100uF leads were at 150ish-uF, the 300uF cap was all the way up at 590uF (though, it seems unlikely a cap would GAIN capacitance over time?) so, this will need to be replaced. Suffice to say, googling 25-228 got me diddly squat, so I'll need to find some other replacement option. Any advice on what to replace it with? (cap pictured in IMG2.jpg)

If you have any questions or general advice, please, let me hear it. Hopefully I got this post in the right spot.

Thanks.

Hi STJ -

First of all Heathkit Oscope models prefix starts with - "IO-" not "10" so maybe correct that.

That big circuit boardy thing I believe is part of a "Delay line" circuit, usually it is done with lots of coaxial cable in a coil.

Old electrolytic caps like that three in one can (second photo) usually have a tolerance of +100% / -20%, so if they are " over" then they are OK.  A fluke meter may not be very accurate on the cap range anyway.

Resistors that say 2W should be of an appropriate size, these days I would put 3W parts in for 2W ones, they may fit, for unmarked resistors 1/2 W might be OK, but I'd still put in 1W or 2W if the space is there.

Looks like a fairly nice unit from how much stuffed in there, and my recollection that it was a higher end set.

Finding caps over 1000 volt rated is getting very difficult these days.  Those 6000 uF. at 15 Volts are likely much smaller as modern caps are quite miniaturized, also "axial" electrolytic caps are getting scarce and pricey.

After doing five minutes of research on this Heathkit model, it seems the most serious problem is likely to be small "drop" tantalum caps catching fire or smoking on the other boards, not present on the PS Boards.  Replace with similar uF. parts having higher voltage ratings, thus a 15 uf / 25 Volt use tantalums rated at 35 or 50 volts.  Associated resistors near these tantalum caps that fail, may also be burned or open causing missing voltages from some circuits.

Good luck with your restoration, post some pix of the front of the set 


Steven

[SilverTailJay]

Thanks for that spelling catch, I've already ordered in some replacements for all the electrolytics, with the exception of the big 3-in-1 capacitor. However, I think I will need to replace that one even knowing the tolerances. there was some nasty black stuff oozing out the bottom of it!
The black, low capacitance high voltage capacitors I will be re-using because you're right, replacements are nigh on impossible to find. I found some nice Cornell Dublier film cap replacements for the yellow 200V ones however, so those particular ones I will replace. They're like 5 bucks a pop, but if they can keep it working for the next 20 or 30 years I'll be more than happy. Also, since I was only able to find one cap in an axial format, I might try hollowing out the insides of the current electrolytics and stuffing the new caps inside. Keep that vintage look and feel. Not that you'd know, since the case will be on 90% of the time.

I'll post some pictures of the front panel when I get home, lots of the knobs are cracked but none are missing! I'll simply need to find a way to fix those.

Thanks for your help.

[SilverTailJay]

Here is a good pic of the front of the unit. The CRT bezel seems to be taped in so I'll have to resolve that at some point.

Also, there's a board directly behind the CRT that looks like it'll be a real pain to remove. Oh well. One step at a time, right?

[Qwidion]

How did the repair go?  did you get it operational?  I have one that I'm working on now, replacing some 7w power resistors in the horizontal final drive section.

so.. a) hoping you got both your saved and operational...
b) If not.. hoping you have some spare parts?  I'm missing the display bezel and graticule.
c) also, looking for the service guide.  Its proving illusive.

Cheers!

[WattsThat]

With Heathkits, the assembly manual is the service guide as a complete description of operation appears along with a schematic that usually show test voltages.

Check online. Schematics are easy to find, complete manuals, not so much. Most are available for purchase in pdf form.

Your only hope for a bezel and graticule are from another IO-4510, they where custom made for Heath. Parts units routinely appear on eBay with the shipping costing more than the scope. While it was an okay 10 MHz scope in its day, it hardly makes sense to spend money to repair one unless you’re a Heathkit collector.

You can count on the original poster of this thread having thrown the whole mess in the trash. I cringed when I saw what was done as it was painfully obvious the OP was clueless about electronics repair.