Omron relay for 9001/not protection relay

[Trnsfmr]

Hi parts gurus,

I'm working on a 9001 and need to replace a low level relay on the 4ch board. It is not the protection relay. On the plastic cover it says type MH4P. I can find some small relays on Mouser, but they look too big. It's a 4PDT. Any body know where to get?

Honest, I tried to find info with the search engine for 15 minutes. All I could find was the protection relay.

??????????

 

[LBPete]

There are a few other threads on AK for people looking for that relay. None have an answer. I searched the internet and didn't come up with much. What is the coil voltage? Are you sure it's bad?

- Pete

 

[Trnsfmr]

Hi Pete,
I've taken the cover off it and cleaned the contacts with a lubricant/deoxidizer called Corrosion X, although they are gold plated and not corroded. I put the cover back and it worked solid for a while, then started to mess up again.

When the relay is energized, those contacts are good. When it's not energized and just the spring is closing the contacts on the other side of the individual DT poles (of 4PDT) the connection is intermittent with two of the four contacts. The relay looks fine, I thought some lubrication might free it up to let the return spring cause better contact.

I spose I could take the relay off the board and disassemble it further, maybe clean the contacts with an eraser, I've heard of doing that before, and put it back together. It might work. I've disassembled potentiometers that didn't work right and have gotten them working again.

I also could buy a small 4PDT relay from mouser and wire it to the pads on the pc board. Seems treacherous, but it could be done.

It's a 24v coil, with 46v running to it through a dropping resistor.

 

[joekid]

I looked for two weeks on the net.O I found sites that would sell you this relay, but you would have to buy 200 at $15. ea.Or you would have to be a repair shop.Or some other BS.So what did I do.EBay, for days I put in the search MH4P.Then before my eyes there were two new MH4P relays. I bid the two and won.I got lucky.But there is a repair shop in Chicago that restores the QRX 9001 that removes these relays and makes the 9001 just 4channel receiver.
Good luck in your guest
Joe

 

[LBPete]

Be careful, MH4P just defines the style and capacity of the relay. Omron generally makes many many coil voltage and terminal variations. Coil variations can be either AC or DC windings. When I was looking on line I saw some 12v coils but not any 24v coils.

In most cases, Omron part numbers are decoded something like this:

MH4P-02-DC24

Type - Terminal type - coil type 02= pc board mount

- Pete

 

[Trnsfmr]

hi,
Well a day later, I guess the Corrosion X started to work. The relay made good and has not ever messed up again. I tested it quite a bit. I've used the Corrosion X to fix old pinball machines before, the ones that use relays for all functions. I have a machine before that would not even start up. I put Corrosion X on everything and a day later it will at least start and run, maybe not all functions but enough to get started.

So, don't need the relay any more, hope I never do!

Thanks, Joe, and Pete, for looking.

 

[joekid]

Jim ,sounds great.Just to let you no,John order the Chips on Friday the 4th .they should be in by Tuesday.Am hoping he will be done with my 890 by then.
Joe

 

[bourvil]

Hello,

I have question regarding this relay so I will resurrect this thread. I have replacement of this relay but the coil is not for 24V as original but for 12 volts. So when using this I must change dropping resistor as well. The power line for relays is 43,5 volts and before this relay there is 820 ohm resistor. Is my calculation right that for 12 volts I will need something about 1k3 ohms?

For original there is drop 19,5 volts (43,5 - 19,5 = 24) and this drop is via 820 ohm resistor (820/19,5=42 -> it takes 42 ohm to decrease one volt). So for 12 volts I need to make drop of 31,5 volts (43,5 - 31,5 = 12) ant for it I need resistor with value of 1324 (31,5*42=1324) ohms

Is this right? many thanks for help or comment.

 

[LBPete]

You might be able to use one of these step up/step down modules.

- Pete

 

[EchoWars]

Pete, that's kind of elaborate for dropping the voltage to the coil of a relay. A resistor will do fine.

Bourvil, just need to know the DC resistance of your 12V coil to calculate a dropping resistor. If it were, say, 1200 ohms (just picking a number here since you failed to give this information), then the coil current is:
12/1200 = 10mA

Now we can calcuate the resistor needed. We need a resistor that will drop the voltage from the source value of 43.5V to 12V (one of several ways of visualizing the problem, but the solution is the same regardless of the method taken to reach it).

43.5V - 12V = 31.5V

So we need a resistor that will drop 31.5V @ 10mA.
R= 31.5/0.010
R= 3150 ohms

Then you calculate the power in the resistor to determine its wattage:
P= I² * R
P= 0.01² * 3150
P= 315mW
...so I'd probably use a 1W resistor just to keep it from looking burnt over time.

This is just an exercise to show how it is done. You need to determine the DC resistance of your coil to find the proper value of resistor to drop the voltage to a proper level.

 

[bourvil]

Many thanks LBPete and EchoWars for answers! I thought that it will not be as easy as it looks so big thanks EchoWars for clearing this problematics

I measured coil resistance and it is 425 ohms.
Then it has current of 28 mA (12/425=0,028)

Next the value of resistance should be 1125 ohms (31,5/0,028=1125) and I am going to use 1,2k resistor which will be 2 watts as original which have reserve in power handling.