Help determining relay function

[DJStrange]

Here is an excerpt from the HFE SU-8080 service manual showing a protection relay HC2A-P-DC24V (bottom left)

I mis-identified this as DPDT (2 Form C) instead of DPST-NO (2 Form A normally open) - the 8 pins in total threw me. I couldn't find any data on the original relay, which would have helped a lot. The only thing I found was an informative post on another forum which mentioned the original was DPST-NO.

Big question is will my replacement relay HC2E-HP-DC24V-F work? Does it require the two pins 1 and 4 to be energised, or would it basically function once but not reset afterwards?


Any guidance would be much appreciated

 

[DrumminDaddy]

It appears from the trace on the service manual that normally closed pins 1&4 are not functional. So pins 5&8 will engage your speakers when the relay is energized. Looks good to me.

P.S. I’d clip pins 1&4 just to make sure they don’t touch any trace when poking thru the board.

 

[DJStrange]

Thanks DrumminDaddy, I think I may have actually identified the relay type correctly, and the forum I read DPST-NO from has either mis-identified or worded their reply confusingly! I'm sure a DPST relay would only have 6 pins, not 8?

Looking purely at the trace and the schematic for the replacement relay, as you say it will perform the function correctly regardless of what pins 1&4 are connected to (nothing in this case).

Thanks again

DJS

 

[century tek]

Is the original relay bad? Just curious.

 

[DJStrange]

Original relay was still functioning correctly last time the unit powered up as far as I'm aware, but I'm replacing it as the clear plastic casing has a little black soot on the inside (is this normal?) and has also got a crack in it - I don't know how it's cracked. Just thought I may as well replace it while the unit's in pieces.

 

[century tek]

Gotcha!

Actually a cracked piece of plastic has no bearing on its function unless tiny pieces were sticking inward and preventing the contacts from opening or closing or gouging the coils but I have never seen this happen.

Black soot could be from the contacts being pitted. This could be caused when there is a significant amount of current passing between the contacts to produce a spark when the contacts open and close. Have you measured to see if there is any DC at the speaker connections?

Could be something simple like bias or DC offset adjustments.

 

[DJStrange]

Thanks Century, the crack looked like a pressure crack, like the case has been pressed a bit hard maybe, but it is only that from recollection. I haven't had chance to look very closely at the relay properly yet but will report back. The amplifier has always run quite hot after being on for half an hour or so, I think the adjustments really do need carrying out as you say - only the T03's on one channel were replaced and there is a ball of white grease round both the thermistors tucked in the heatsink so there is much to investigate while it gets cleaned!