pushing transistors back into circuit board

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Old 01-31-13, 11:57 AM
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pushing transistors back into circuit board

I'm following some calibration instructions for an old Heathkit bench multimeter built in the 70's probably. One step of the instructions is to interchange the position of two separate transistors on the circuit board, and to make sure when doing so that the transistors are properly reinstalled. These are three-legged transistors of which each of the fine wires pushes in/out of its own sleeve-type connector on the board. Here's a few pictures with pencil pointing to the specific transistors I'm referring to.
http://i207.photobucket.com/albums/b...ps11fbd32d.jpg
http://i207.photobucket.com/albums/b...ps811cee70.jpg
So as carefully as I could with a small pair of needle nose pliers I pulled each transistor and then reinstalled it the interchanged locations as instructed. However, afterward I'm not getting any of the readings I'm supposed to look for on the LCD readout, and am suspecting I may not have reinstalled those fine wires back into those sleeves properly. Can't really tell if they're making the connections down in those sleeves as they should and not sure if each of the three pins on both of the separate transistors are actually in the proper sleeve or whether that makes any difference. I tried several times to see if I could push those wires in securely down into those sleeves but really unsure of the proper method to do this. Any comments/advice about this appreciated.
 
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Old 01-31-13, 12:09 PM
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If you followed the picture on the board with the flat on the transistor matching the flat on the picture, then the EBC is correct. Those are not typical transistor sockets, but a pin by pin solution. If you can see the lead going into the socket, it should be good. The one to the left looks like the Emitter lead could be pushed in a bit farther. I use needle nose with smooth jaws so I don't score the leads, which can cause them to break with a few bends.

Difficult when you are repairing the meter you need for troubleshooting. Do you gave another meter?

Bud
 
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Old 01-31-13, 12:27 PM
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Wow! I have not heard "Heathkit" in a long time. I still have a scar from the soldering iron when I assembled my first Heath kit when I was 8 or 10. I'd love to see some photos of your multimeter.

How often you change the transistors? If it's something you almost never do and you feel it's a connection problem you could just solder them in place.
 
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Old 01-31-13, 12:33 PM
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On transistors like this is the emitter lead the middle one between the other two?
 
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Old 01-31-13, 12:38 PM
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Here's a pic, PD. http://i207.photobucket.com/albums/b...ps69a62f93.jpg
There's a rather extensive/involved procedure to get it re-calbrated. I'm trying to follow the instructions, one step of which was to interchange these two resistors and proceed from there.
 
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Old 01-31-13, 12:41 PM
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It can vary......but based on all the others on the board, looks like the emitter is to the left when looking towards the flat portion.
 
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Old 01-31-13, 12:52 PM
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I should post a pic of my old Knight kit multimeter. It makes your Heath look state of the art.
My Heath SB-301 receiver is still functioning, although I seldom fire it up.
 
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Old 01-31-13, 01:16 PM
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Dang! I'm sure now I got the right leads of those transistors into the right spots. But still not getting either of the readings I'm supposed to see, so don't know how to proceed now. Here's the site where the calibration instructions (PDF) can be downloaded: HEATHKIT IM SM 1210 DMM CALIBRATION INSTRUCTIONS 1975 SM Service Manual free download, schematics, eeprom, repair info for electronics
I'm stuck now toward the end of the DC calibration set of steps, toward top of page 44 there. Where it says to interchange those transistors and look for either of those two readings. I don't get either of those two readings but instead get an odd 1.88 readout regardless of location of those two transistors. All was going smooth until I removed/replaced those...
 
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Old 01-31-13, 07:33 PM
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You've got them in the right direction.

heathkit part # 417-213 crosses over to an NTE-123AP and uses that basing diagram.
 
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Old 01-31-13, 07:50 PM
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Kept getting that same odd readout instead of either of the two the instructions say I should see. Figured I must not be getting good sound connection(s) by my attempts to push those blasted wires down into those sleeves where they catch right, so kept fiddling with it until finally one of the fine wires broke off at the head of the transistor. Now I wonder where I could try to get another replacement transistor just like the one I broke if I was so inclined to persist in trying getting this thing calibrated.
 
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Old 01-31-13, 08:11 PM
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It's a very generic transistor. Low level audio amp.
2N3904 or BC547 or NTE123AP are all valid replacements.

I'd go for the 2N3904. I'm not a big fan of NTE parts.

Also......you'll need to change both. Keep the circuit balanced.
 
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Old 01-31-13, 08:12 PM
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Are there any numbers on the transistor, 2N??? or other. Since they wanted you to swap them the two are the same. If not, do they provide a schematic showing these devices. Transistors are still available and should be rather generic in this application, just may need to be matched, but probably not.

Bud
 
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Old 01-31-13, 08:21 PM
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The only numbers on these two identical transistors is the Heathkit part number (417-213). Thanks PJ for the crossover numbers. Found this on ebay but has to ship from Thailand.
30 x 2N3904 Transistor NPN 40V 200mA to 92 Free Shipping | eBay
Or there's this 20 x BC547 Transistor NPN 45V 0 1A Free Shipping | eBay
but there is difference in voltage and amperage specs between the two.
 
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Old 01-31-13, 08:33 PM
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try mouser.com for quick service.....small quantities.

2n 3904 | Mouser Electronics, Inc.
 
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Old 01-31-13, 08:39 PM
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Great. Thanks!
 
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Old 02-01-13, 06:57 AM
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I'll try and remember to see what parts I have in stock at home. If it's a pretty generic one I may have it for working on old pinball machines.
 
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Old 02-01-13, 10:47 AM
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I thought I might mention that in another Heathkit parts cross reference database I came across, a generic name of 2N5249 came up in a cross reference query for my Heathkit transistor 417-213. I suppose that's just another valid replacement, among perhaps several or maybe many others?
 
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Old 02-02-13, 06:51 AM
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I checked and the closest I have is a SCR 2N5060 intended more for a power supply or switching circuit I think and I don't think it will work for your meter.
 
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Old 02-02-13, 07:20 AM
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If you can't find one, let me know. That NTE123AP looks very familiar, and I probably have some or something similar if I haven't tossed them. I sure hate throwing this stuff away. Just have to find it.

Bud
 
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Old 02-02-13, 11:05 AM
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Thanks. If I have no luck obtaining a valid replacement otherwise for less cost, my final option will probably be to order a couple of those 2N3904's from Mouser (only 36 cents each) but the $4.49 minimum shipping cost from there is scaring me away. I'm cheap I admit it.
When/if I do ever obtain the replacement part(s), on these "non-typical" transistor sockets such as I have on this board (as seen in pictures first post this thread), I'm still unclear about the proper method of pushing the fine wires down into those sleeves to make good contact and without bending up too bad or even breaking a wire on the transistor (like I aleady did with all my fiddling around with it). I do have smooth-jawed small needle nose pliers to try to push the wires down in but still seems like I'm not doing it right, and can't really be sure the wires are making proper contact down in there. Any more comment to that regard would be appreciated also.
 
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Old 02-02-13, 11:26 AM
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Yeah......there's no getting away from the minimum shipping charges. I keep a list of parts that I need to replace and then when an immediate need arises...I order the whole bunch.

You should not need any tools to push the transistors into those sockets. The pins don't hold that tightly. Try to not bend the leads of the transistors because once that happens it makes the job a bit harder.
 
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Old 02-02-13, 11:36 AM
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Ok I can try not to bend the leads but seems almost impossible not to bend as they're all of equal length and by the time you get one wire pushed in a little ways the other two are already down lower on the outside of the sleeves (pins) inserts so gotta bend em up a little then stick down in. Unless maybe cut two of the leads a little shorter but I doubt thats a good idea either? Also, if the pins don't hold that tightly, do they maybe start to hold even less tightly the more you might push wires in and take em out again, like I've been doing, and then not hold tightly enough?
 
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Old 02-02-13, 02:03 PM
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The root problem is that that component is not designed to be used like that. Its fine leads are designed to be inserted into a hole and soldered. If you will be swapping it often I'd consider a totally different approach. Maybe some alligator clips on wires that you can clip onto the transistor's leads or get some proper male & female sockets and solder the transistor into the socket.
 
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Old 02-02-13, 02:54 PM
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Yeah PD that makes sense doing one of those things. I'm not confident at all that I'm making adequate contact by pushing those fine wires down into those sleeve insert things; seems loose and highly questionable about the soundness of the contact in there, to me anyway.
 
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Old 02-02-13, 05:50 PM
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Update: Got a few 2N3904's on the way to me soon, for free! (thanks to the kind generousity of a forum member here). Thanks for all the helpful responses here. You all rock. Will keep ya posted if I have any further luck, good or bad, with the recalibration and getting that ol' multimeter working right.
 
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Old 02-02-13, 05:56 PM
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Take one of the damaged transistors and using one leg at a time.....try it into those pins. It doesn't have to be very tight.
 
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Old 02-10-13, 01:50 PM
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Okay I received and have now installed the replacement resistors (as I mentioned previously I broke the wire off the head of one of my original ones). I managed to successfully insert them into the connectors on the board this time, and was able to get the multimeter recalibrated, and seems to be working fine now.
 
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Old 02-10-13, 02:31 PM
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Success feels good doesn't it? Thanks for letting us know how it worked out.
 
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Old 02-10-13, 03:11 PM
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Very good,
I'm more sympathetic to old things, now that I'm one of them .

Bud
 
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