Hobart 493400 Auto idle board repair.

DJB6.03CE

Member
I’d like to source all the parts for this simple timer board.
I have worked on a 74 Hobart gr303 that the board was toast in.
I’ve got a newer machine Hobart powerweld 6500 similar to a Hobart champion 16 apparently the same obsolete board.
This board is not working but all the components are identifiable.

I’ll post some photos and maybe you can help me make the correct repair component list. Hopefully be of help to others with this common failed board.

1986 board Hobart powerweld 6500




1993 board Hobart champion 16



1996 board


1974 idle control board schematic Hobart GR303



R1
R2
R3
R4
R5
Q1 2N6427 Mouser 610-2N6427
Q2 2N4921 Mouser 2N4921G
Q3 2N3903 Mouser 610-2N3903
C1
CR1
CR2

---------- Post added at 05:49:15 PM ---------- Previous post was at 05:34:49 PM ----------

R1
R2
R3
R4
R5
Q1 2N6427 Mouser 610-2N6427
Q2 2N4921 Mouser 2N4921G
Q3 2N3903 Mouser 610-2N3903
C1
CR1 1N5395 Mouser 625-5395-3/54
CR2
 

DJB6.03CE

Member
R1 56k @10%. 1/2 watt
R2 47ohms 10% 1/2 watt
R3 470ohm 10% 1 watt
R4 820ohm 10% 2 watt
R5
Q1 2N6427 Mouser 610-2N6427
Q2 2N4921 Mouser 2N4921G
Q3 2N3903 Mouser 610-2N3903
C1 WBR1000-16 Cornell Dubilier Obsolete but still NOS available
CR1 1N5395 Mouser 625-5395-3/54
CR2
 
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cobbadog

Active member
Firstly I am NOT an electronics person but both the 1986 and the 1993 look very similar but using slightly different and possibly upgraded components.
It was my belief that transistors were identified by the coloured bands around them and the capacitors have their values on the labels. There are 2 components that I don't know what they are but an electronics shop will be able to identify.
 

Zephyr7

Active member
Q1 on the schematic is an SCR, not a transistor. It’s drawn backwards on the schematic though (usually the slanted line comes off the other end of the diode in an SCR symbol), I’m not sure why they did that. It might just be an error on the drawing.

The original dark brown cylindrical body resistors are all carbon composition. Those resistors tend to absorb moisture overtime and their value drifts away from what it should be. Don’t use them in a rebuild, modern resistors are better. The updated pics shows rounded off cylindrical tan body resistors, those will be carbon film. Their values are on your schematic, you read them left-to-right from the color bands with the gold or silver band on the right end. The new board shows one big blue bodied resistor, that’s probably metal oxide. I’d use a metal/ceramic composition here just to be safe, such as the ohmmite OY series (green body). The OY resistors are pretty indestructible. It might be overkill though, it depends on the application, but I doubt the welder is an easy service for the parts.

I’d use 1N4007 diodes for the black diode (CR1), but it’s not super critical. I have lots of that diode type is all. They are 1A silicon diodes, 1,000v PIV. You’d probably be fine with a lower voltage diode, but they all cost about the same in that series so you’re safer with the higher rating. The glass body diode (CR2) might be a 1N4148 or 1N918. The number should be printed on it around the perimeter. Those are 1A diodes too, and nothing fancy. You could probably use a 1N4007 here too without any problem, but if you’re ordering all new parts, best to try to get an exact replacement. Glass body diodes are still readily available.

The big capacitor is a 1000 microfarad (uF), 16v polarized electrolytic cap with axial leads. Axial leader caps are much less common than they once were, but they’re still available. Yours appears to be an 85*C temp rating. If you get a higher temp rating it will last longer. I’d go with a 1000uF 25v cap. You can probably get one with the same physical size for a nice replacement. The new one might be a different color but don’t worry about it.

C2 is probably ceramic disc cap. Nothing fancy. I don’t see it in the pics but it’s on the schematic. Just get one with the same capacitance rating and at least 100v voltage rating. C4 might be a film cap.

Note that the schematic does not appear to match the board you show in those pics. I’d read the values off the parts on the board and order those. The transistors that are small are TO92 packages. The big one looks like a TO138. The small ones are a 2N3903 and a 2N6427 I can’t quite make out the marks on the large one, but it will be 2Nxxxx where those x’es are four numbers to make up a full part number. You probably won’t have any trouble finding any of the three to order, they’re all normal silicon parts (it’s the old germanium and point contact transistors that are hard to find now, but your stuff is too new for that).

I usually use Digikey and I’m sure they will have everything you need. I use Mouser occasionally too, and they should also have everything you need.

I hope this info helps. Sorry i didn’t see your pm until today.

Bill
 

Zephyr7

Active member
One thing I forgot to mention about the resistors: the physical size is part of the wattage rating. The little ones are probably 1/4 watt, maybe 1/2 watt. The big one could be 1, 2 or 5 Watts. When in doubt, use a higher-wattage resistor to be safe. Just make sure the size you get physically fits the spot on the board where it needs to be mounted.

Bill
 

Zephyr7

Active member
Now you have everything you need to rebuild that board without guesswork! Excellent!

Q1 is a darlington transistor, which gives higher gain. Think “amplifier that can amplify more”. Standard type of part.

Both diodes look to be for protection, CR2 to protect from input reverse polarity, and CR1 to protect against back EMF from the solenoid. Neither is very critical in terms of exactly what diode you choose to use. I’d use 1N4000 series diodes in both locations, 1N4004 or better (the last number is just the reverse voltage rating, higher is better). Neither diode is ever going to see anywhere near 1 amp, so you don’t need anything beefier.

The schematic gives wattage values for the resistors too which is one thing that you’d otherwise have to guess at so now you can be sure to get the right values.

Bill
 
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