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Author Topic: Repair of Time Delay Relay  (Read 1166 times)
K8AXW
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Posts: 3777




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« on: July 20, 2011, 09:16:35 PM »

Greetings all:

I have a problem.... and so far I haven't been able to solve it.  After I explain the problem, you'll see what I mean.

In my homebrew amplifier I use two Syracuse Electronics Corp. time delay relays.  On in the filament circuit and one in the HV step/start circuit.  I also had a spare, which I found necessary to use recently.  The defunct relay needs repaired and therein lies the problem.

The circuit is fairly simple, using a couple electrolytic caps, a couple disc caps, a few resistors  a relay, a pot with a knob, another thumbwheel pot and a small transistor.  It is an octal plug-in relay.

The relay info is: Part Number - TER00308 - 110VAC - 10 Amps - Serial number F-1200 4565.

Syracuse Electronics Corp. is no longer in business.  I can get it repaired commercially but will cost me $65.00 which I can't afford.  So far I've determined that one of the electrolytic caps is bad and have located a replacement for it.  The single transistor is also bad and has the number GE 544 on it but I can't find that number listed anywhere and cannot cross reference it.

I think it is a PNP but I'm not sure and have no idea what voltage/current parameters to use for a possible substitute or even if it is for sure a PNP.

So far the tracing of the circuit on the PCB has been an exercise in futility for me.  But I haven't given up on this.

So, in the meantime as I try to figure this out, I'm posting it here in  case someone out there has not only used these old relays but has also knows what circuit they use or at least what kind of transistor they use.  (I'm finding it difficult to believe that this little transistor, about the side of a 2N2222A is carrying the relay coil current!)

I am not interested in buying a new relay because every one that I've seen costs between $100 and $275.00!  I am not interested in replacing the relays with solid state timers because that would require another power source that is always "on" which I don't want.  Now, when I shut the amp down, it is DEAD!


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K9YLI
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Posts: 859




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« Reply #1 on: July 21, 2011, 07:47:40 AM »

 marlin p jones..     mpja.com

pn 18297-rl      delay realy  but  its  24volts  ac/dc coil.

$9.95.. 5a 250 volt contacts.  delay  .5 to 30 seconds.

yes you may need a  24 volt  ps.  but then as the other relays fai.
you aready have it.

and/or  you may use the delay realy to pick nother relay to switch the volts/current you need.

pnp and  npn..  just figure the  voltage on the collector. 
plus is a   pnp..   
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K8AXW
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Posts: 3777




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« Reply #2 on: July 21, 2011, 08:04:15 AM »

K9YLI:

Thank you for the info.  Will file that... just in case.  If I'm not able to repair this relay my options are many.  Including a relay driving a relay...or a solid state circuit driving a relay.

The reason I have pretty well determined the bad transistor is a PNP is because of the plus side of the bad electrolytic is connected to the collector.

Last night I took the relay apart and scanned the PCB and today I hope to 'connect' the components between the pads.  This is quite time consuming and the results sometimes just doesn't work out. So that is why I'm hoping that someone here can save me a lot more work.

Thank you for your input.
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KA5N
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Posts: 4380




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« Reply #3 on: July 21, 2011, 08:20:56 AM »

How did you determine that the GE device is a transistor?  It might well be an SCR as an
SCR is a latching device.  If the positive end of the electrolytic is connected to what you think is a PNP transistor, I think you made a mistake somewhere.  The collector of a PNP transistor goes to negative and the emitter goes to positive.  If it is a transistor and is from GE is may well be a germanium PNP made in the early 1960's.
You would be miles ahead to find a replacement for the whole unit (of which there are
hundreds of types and prices available.... Just takes a little looking) or design your own
delay timer, which for me would be easier than repairing an old device with untraceable and probably unobtainum parts.
Good Luck
Allen
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AD4U
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Posts: 2158




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« Reply #4 on: July 21, 2011, 08:25:54 AM »

Apparently the transister is used as a switch to energize the relay.  Most of the other components are used as the delay circuit.

It should be a relatively simple matter to measure the voltages around the transistor to see if it is NPN or PNP.  Depending on the circuit design, either could be used for this purpose.  Once you determine which, just use any old switching transistor with adequate current rating to switch the relay coil.

Heck if all else fails and as a last resort, tack solder in which ever type transistor you think it is and see what happens.  If it works then everything is OK.  It nothing happens or if the $0.50 transistor POPs, try the other one.

Even doing this and if you tack solder in the wrong type transistor, I don't think you will permanently damage any of the other components on the board.

Dick  AD4U
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KE3WD
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Posts: 5694




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« Reply #5 on: July 21, 2011, 08:44:08 AM »

The reason I have pretty well determined the bad transistor is a PNP is because of the plus side of the bad electrolytic is connected to the collector.

Rethink. 

If the + of an electrolytic is connected to the Collector of the transistor, then the transistor is NPN. 

You have another way to find out as well, since you stated you have a working identical relay.  Open that one up and use the ohmmeter on Diodes scale to find out if the transistor is NPN or PNP.  The majority of single transistor relay coil drivers encountered are going to be NPN type, BTW. 

You mention the ubiquitous 2N2222.  I would find that one to be rather light as a relay driver, suggest you look at the 2N4401 instead.  Or any of a number of NPN amplifying or switching transistors in that class, including EIAJ parts such as 2SC828, 2SC945 - watch for pinout differences and install accordingly. 

If you aren't sure how to tell an NPN bipolar from a PNP using your ohmmeter's diode scale, now's the time to get over that simple hurdle.  The first thing to know is which lead of the ohmmeter actually has the Positive voltage on it, with any of the modern DMM's it is very likely to be the Red probe.  With Positive going lead on the Base of the NPN transistor,you should read about 0.6 to 0.7V from Base-to-Emitter and Base-to-Collector.  Of course, the opposite would apply to the PNP type. 

73
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K8AXW
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« Reply #6 on: July 21, 2011, 07:55:56 PM »

ya know guys, at this point, I'm not sure of anything!  I did attempt to check the transistor (SCR) in the working unit but I couldn't get the clip leads connected.  I was being pushed for time and so instead of putting the relay into my octal test socket and powering it up and then checking the underside of the PCB, I just reassembled it and plugged it into the amplifier and put it back on the air.

I've run off copies of the PCB, foil side and have inserted the components between the pads and now I have to run the leads from the relay to the PCB and then see what this thing is actually doing.

I noticed just this evening the the relay coil has 4 terminals on it!  A quick ohmmeter check shows no continuity between any of the coil terminals, but does show capacitor charging.

Tomorrow I'm going to pull the electrolytic and recheck this coil.

In the meantime, the spare relay in my filament time delay has gone from a delay of 6 seconds up to 28 seconds!  I don't know if I'm in the process of losing a cap on this relay or what. 


I think perhaps it's time to redesign the whole damn timing thing and get rid of these very old and obsolete relays!
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K8AXW
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Posts: 3777




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« Reply #7 on: July 21, 2011, 09:08:42 PM »

BTW.... about the PNP/NPN polarity..... I guess this is just one more thing that I'm losing!  Researched that and found that I was wrong.... you guys are right. 

"Golden Years", my ass!
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