SDT-S-112DMR relay - where to buy in qty = 1

[retiredcaps]

I think I have a bad relay switch in an AVR receiver (Harman Kardon AVR 125). It is made by Tyco and the part number is SDT-S-112DMR. I checked the usual places like digikey (not available) or mouser (it is available, buy minimum order is > 380).

Anyone know where I can just buy 1? The search engine comes up with a lot of wholesale sites where the minimum quantity is 1000. Or does anyone know of an equivalent to this relay switch?

When I turn on the receiver, it should make a click sound (from the relay) and the standby light should turn to yellow.

There is a ceramic cap just in front of the relay and it could be bad as well, but it is very difficult to access both components are they are on the bottom (main PCB) and it will require a lot of time to take apart everything to get to these two components.

[smason]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I'm not saying the relay hasn't failed, but I would be surprised.
I used to service equipment that had relays, and they rarely fail. Sometimes they get flakey contacts, and I would pop the covers off and run a burnishing tool or fine sandpaper thru them, that almost always solved the problem. Not very often do they fail to actuate.

I'd definitely test it first before killing yourself trying to find one. I'd take it out of circuit, measure the coil, and test the diode (if there is one across the coil) then apply voltage and measure the contacts.

[Toasty]

Re: SDT-S-112DMR relay - where to buy in qty = 1

A relay not engaging in an amp is usually a sign of an output failure. What does this relay connect to? The speakers?

There is a sense/protection circuit on most of these units that detects DC on the output from the amplifier transistors. It shuts off (or in your case, fails to connect) the output to the speakers to prevent damage to them if it sees a fault. Sometimes even a short on the speaker leads will cause a shutdown.

Toast

[Agent24]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Often you can find small quantities of parts on eBay if the usual suspects only want to sell you thousands

But like the others said, it could well be something else at fault.

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I have attached a small snapshot of the schematic from the service manual that what I thnk is the revelant part. It is RY94. It is the only relay listed on the part list of the service manual.

A relay not engaging in an amp is usually a sign of an output failure. What does this relay connect to? The speakers?

There is a sense/protection circuit on most of these units that detects DC on the output from the amplifier transistors. It shuts off (or in your case, fails to connect) the output to the speakers to prevent damage to them if it sees a fault. Sometimes even a short on the speaker leads will cause a shutdown.

Toast

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I looked at ebay, but there are no sellers.

I agree that it may not be the relay. It could be something else, but since I don't hear the click, I thought I would start there and either work forward or backwards from there.

Unfortunately, on this AVR, the main PCB board is at the very bottom and very difficult to access to get readings.

Often you can find small quantities of parts on eBay if the usual suspects only want to sell you thousands

But like the others said, it could well be something else at fault.

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Okay, I realize now maybe I should have described the problem in detail and then ask if the relay is at fault. Sorry, my bad for jumping ahead.

So let me start over.

I purchased a non working Harman Kardon AVR 125 receiver to learn more about electronics.

When I hit the power button, it should make the standby LED go amber. Then if it I hit the standby button or hit remote power on button, the relay should click and the AVR should be operational (the standby LED should be green).

What actually happens is this. I hit the power button and the standby LED is green and the entire front panel is list, but not operational (no sound if I hookup speakers - none of the buttons work to change settings). When I hit the standby button or hit the remote power on, there is no relay click.

There are 5 fuses and all check okay (0.3 ohm or less). I have verified there is main power going to the main PCB by plugging something into the back of the AVR 120V outlet.

I see there is a standby transformer (T902) on the main PCB. I believe this is for the remote control and standby power.

I found the service manual at



and have started to learn how to read schematics.

[smason]

Re: SDT-S-112DMR relay - where to buy in qty = 1

If I'm reading the schematic correctly the only thing that relay does is switch the rear switched AC outlet on. So the fact that it's not clicking is the symptom of a bigger problem.

[Radio Fox]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Have you tried doing the processor reset?

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I can't do a processor reset because the standby LED is green (on - not in standby mode). That is, I can't get the AVR 125 into standby mode.

According to the manual, in order to a processor reset,

"To clear the AVR 125's entire system memory including tuner presets, output level settings, delay times and speaker configuration data, first put the unit in Standby by pressing the System Power Control Button.

Next, press and hold the Tone Mode button for three seconds. The unit will turn on automatically and display the RESET message in the Main Information Display."

Have you tried doing the processor reset?

[kc8adu]

Re: SDT-S-112DMR relay - where to buy in qty = 1

that relay turns on the primary of the main power transformer and the accy outlet.
and it may be bad.see if q901 is switching.

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Thanks for the suggestion. I'll test Q901 (KTA1271) now that I found the datasheet for it. I have to put this aside for now until next week. I can't leave the AVR all pieces lying around this weekend.

I know the next major electronic purchase I make, I will look at the service manual first to see how easily I can take apart and reach things.

that relay turns on the primary of the main power transformer and the accy outlet.
and it may be bad.see if q901 is switching.

[arrudi]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Hallo,
according to the turn on Procedure, You should check, that the relay contacts are defenitly open.
Turn on MOMS switch only, measure that there is no AC Voltage at F901 and F902.
If there is any, then You have a problem with the relay contacts (sticked together).
Reason: acc. page 22 only the ST +5V (Standby 5V) should be present.
The system should be in Standby with amber light on.
Now press the "System Power Control" switch. Normally this will actuate the relay and applies power to the main transformer.
Q901 operates the relay. The controlling signal is named Power_H.
See page 77 and page 79 to trace the signal. It comes via BN80 and CN80 from the IC72(96).
The System Power Control switch S701 connects to IC72(38), Signal named Key_1. It connects via BN88 and CN88 to S701.
Good luck!
Ascan

PS: Please excuse my English, but English is not my native language.

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Thank you for the suggestions and your english is better than most who are born in North America.

The AVR has very tight spacing and getting DMM probes to F901 and F902 is nowhere near as nice as shown on page 22. The chances of probes slipping with live AC is very high and I would rather not take that chance.

My plan is to take apart everything later on and test the relay and Q901 out of circuit (if possible).

Hallo,
according to the turn on Procedure, You should check, that the relay contacts are defenitly open.
Turn on MOMS switch only, measure that there is no AC Voltage at F901 and F902.
If there is any, then You have a problem with the relay contacts (sticked together).
Reason: acc. page 22 only the ST +5V (Standby 5V) should be present.
The system should be in Standby with amber light on.
Now press the "System Power Control" switch. Normally this will actuate the relay and applies power to the main transformer.
Q901 operates the relay. The controlling signal is named Power_H.
See page 77 and page 79 to trace the signal. It comes via BN80 and CN80 from the IC72(96).
The System Power Control switch S701 connects to IC72(38), Signal named Key_1. It connects via BN88 and CN88 to S701.
Good luck!
Ascan

PS: Please excuse my English, but English is not my native language.

[arrudi]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Hallo,
sorry, I overlooked something.
Just measure the AC voltage in the switched rear outlet.
Have a nice sunday.

[retiredcaps]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I don't have to measure anything there. I already plugged a 120V device into the back of the rear switch outlet and there is definitely power when I press the MOMS switch.

Just measure the AC voltage in the switched rear outlet.

[stj]

Re: SDT-S-112DMR relay - where to buy in qty = 1

check none of the front panel buttons are stuck or shorted.

i had similar problems on old sony tv's

[Regenpak]

Re: SDT-S-112DMR relay - where to buy in qty = 1

Is it just me or are there two Q901s in this weird amp?!? There's a regulator Q901 (2SA1271Y, page 73, -30V for the display) and the relay transistor Q901 (2SC2785Y, page 76) that switches RY94 (main power) on. Kinda split personality or something.

[kc8adu]

Re: SDT-S-112DMR relay - where to buy in qty = 1

2 different boards with reuse of designations.

[arrudi]

Re: SDT-S-112DMR relay - where to buy in qty = 1

I think, You got a bad relay. There should not be any AC at the rear switched outlet, when only the MOMS switch is on.
Turn power off, tap the relay a couple of times, may be the sticked contacts opens.

I don't have to measure anything there. I already plugged a 120V device into the back of the rear switch outlet and there is definitely power when I press the MOMS switch.