EP3 Echoplex Resistor Burning

[Chinoz71]

Hello All,

I have an early solid state EP3 serial #12774. It appears to be a '71 or '72 model. The 22 ohm resistor in the solenoid power circuit is heating up excessively and burns up. This model has the high voltage solenoid circuit, 140v i think, and not the 24v.

Also the solenoid coil (B23-253-A-1) is making a buzzing sound but still engages the pinch roller arm. This is the schematic for this part of the circuit:




Here is the sound of the solenoid engaging and buzzing:

https://www.youtube.com/watch?v=72f_XFzYw0I

Here is the buzzing and the resistor smoking afterward:

https://www.youtube.com/watch?v=uDxS7Zw2TQE


Has anyone ever seen this issue before?

Thanks for you help!

[52 Bill]

Has anyone ever seen this issue before?

Thanks for you help!

It doesn't matter if anyone has seen it before or not, there is a problem with the circuit.

The resistor will only get hot if there is too much current being pulled through it. The three things that could cause that are the filter cap, the solenoid and the circuit wiring. In another post you said that you already have replaced the cap, so that leaves the solenoid and the wiring. It should be fairly easy to inspect the wires and component leads. Make sure nothing is shorting to the chassis, etc.

Inspect the solenoid and see if it looks like it has been physically damaged in any way. Measure the resistance of the coil (power off) and check to see that the coil is not somehow shorted to the case ground.

Worst case, you will need to replace or rebuild the solenoid coil.

[Chinoz71]

Thanks Bill. I was leaning toward the solenoid as well since the circuit has so few components and all of them have been replaced.

I have removed the solenoid from the circuit and tested the resistance between the terminals. I am reading about 75 ohms. I also tested from each terminal to the solenoid frame to test for any shorting but nothing there. Also checked voltage at the coil which should be 140v according to schematic but I am only seeing 50v.

I think I might have to send the coil out to have it rebuilt. Any recommendations on who can do this?

Thanks!

[52 Bill]

Also checked voltage at the coil which should be 140v according to schematic but I am only seeing 50v.

What voltage do you read with the solenoid out of the circuit? And does removing the solenoid from the circuit stop the resistor from burning?

There isn't much to the solenoid, just a coil of wire. Can't you do it yourself? Just carefully dissect the original one and rewind it back like it was. I would think that the hardest part would be measuring the gauge of the original wire.

[Chinoz71]

Hi Bill,

With the solenoid in the circuit i am reading 168v across the solenoid wires. The schematic shows that the circuit should be 140vdc after going through the diode and resisitor. Not sure if that circuit voltage will allow for deviation in the 10% - 20% range. A 20% deviation would put the voltage at exactly 168v. With the solenoid out of the circuit the resistor does not get hot at all.

I think i can reverse engineer the solenoid coil but since i have never done it i will have to research how its done so i can get the correct winding count if its even needed as well as getting it to work at the correct operational voltage. It looks pretty easy to do.

[Enzo]

With the solenoid gone, ther is no path for current to heat the resistor.

Rectify 117vAC and filter it, we get naturally about 165 volts DC. So unless I am still groggy from sleep, that means about 25v dropped across the 22 ohm resistor. And that means it has to dissipate 25-30 watts. It needs to be a 50 watt resistor. Or have I missed something?

[Chinoz71]

Thanks Bill,

Not sure what the original wattage spec for the resistor was but it does make sense that it would need to be a high wattage resistor. When I bought the unit there was a burned up 1/4 watt resistor in place so thinking along the same lines I put in the 2 watt resistor that is in it now but when that started to smoke I started looking for faulty components or a short. Do you think that having the wrong wattage rating resistor could cause the voltage to the solenoid coil to be lower than needed and in turn cause the solenoid buzzing/ chatter in the videos?

[Mark Black]

Just thought I'd add some info...

I notice in the Echoplex Owner-Service Manual on page 26 there is a picture of the top & inside of an EP3, showing an obvious sandblock resistor attached to the solenoid supply terminal board. Hard to make out if it's labeled as 220 or 22(omega symbol), but it looks like a 5W judging by the relative size. This is regardless of the schematic saying all resistors 1/2W unless otherwise noted (wouldn't be the first time a schematic had an error).

Edit: I see the resistor is indeed a 22(omega) (22 ohms) in one of the pictures at post #9 here: http://music-electronics-forum.com/t40580/

I also note on page 38, Index No. 57, the solenoid is listed as a 115V unit for s/n 12960 and below. That's probably the AC RMS rating.

Manual is currently available here in fairly hi-res (approx 24MB):
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8& ved=0ahUKEwjr37PNgcjUAhVJ8WMKHa_zC6cQFggiMAA&url=http%3A %2F%2Fwww.synfo.nl%2Fservicemanuals%2FMaestro%2FECHOPLEX _OWNER-SERVICE_MANUAL.pdf&usg=AFQjCNE7B3RQXTo8B_uo-4he7gRf9HVI_g

[salvarsan]

The 22 ohm resistor connects to a diode.
Check its health, too.

[Chinoz71]

Mark,

Thanks for your observations. i downloaded the manual and ordered some 22 ohm 5 watt resistors. i am going to try that and see if it helps. I'm not sure if that will fix the solenoid buzzing chatter sound that is happening when i turn the unit on. Let's hope so because those solenoids are near impossible to find NOS or even used.

The only way to approach a solenoid issue would be to rebuild it. Like I said in my previous post all the circuit components have been replaced (Diode, Resistor, and Capacitor) with the exception of the solenoid.

I'll reply with my findings...\m/

[Chinoz71]

Thanks Salvarsan! All components in the circuit have been replaced but i ordered a higher wattage resistor to test with.

[John e wahd]

How did you make out with the solenoid issue. I had a similar problem and was looking forward to your result chinoz71
I wouldn’t mind an explanation on how to rewire a solenoid like this one since they are near impossible to find.