ILP HY248 module sometimes with and sometimes without DC on output

[simple simon]

I have acquired an amp which uses two ILP HY248 modules and a single ILP power supply.

When I turn it on I get ~10v across the outputs, but only if there is a load/speaker attached. If there is nothing attached there is no voltage and no voltage appears if a load/speaker is subsequently attached.

If, however, I start to put in a signal, one of the modules develops a DC voltage and one does not.

Any ideas how to fix this? Given that they are modules there is not much I can fiddle with. Can both be broken in the same way?

Many thanks,

Simon.

[Mooly]

So is one module working OK ? and drives a speaker OK ? as you say only one develops the offset, yet ask if both can be broken the same way.

I remember ILP modules from 30 odd years ago when I first started reading electronics magazines... so I have no idea how old your are.

As with anything, check the basics... is the power supply OK and the modules getting the correct voltage. Is it a split supply -/+ voltage ? are both rails correct.

I wouldn't hold out to much hope tbh... but you never know

Found a connection diagram here,
Discontinued Products

[event horizon]

I should imagine the chances of finding another HY248 module are like looking for horse feathers

If it turns out to be the module then i'd use a philosophy i used when i realised i had a set of totally gummed up carburetors on my FZR1000. If it's broken you can't break it any more! I used denture cleaner & it worked a treat

Look around for something to dissolve the potting compound on the back of the heatsink. Acetone might do it, though i'm sure other stuff similar may well shift the stuff to.

Only reason i mention this is because i have seen motorcycle ignitors that were "potted" up stripped down the same way to modify & or repair them. I happen to have a few HY60 here so they most likely are potted up in a similar way.

Don't give up yet

[paulb]

Sounds like a lot of work. I'd replace the modules with something more current.

[nigelwright7557]

Originally Posted by simple simon

Given that they are modules there is not much I can fiddle with. Can both be broken in the same way?

Many thanks,

Simon.

We used to get into potted modules by using a solvent.
Sorry cant remember which one now.

[simple simon]

Originally Posted by Mooly

So is one module working OK ? and drives a speaker OK ? as you say only one develops the offset, yet ask if both can be broken the same way.

I remember ILP modules from 30 odd years ago when I first started reading electronics magazines... so I have no idea how old your are.

From notes scribbled on the side they are 1995 vintage. One will drive a speaker but only if it is not connected at switch-on otherwise it starts with a DC offset. Both rails are as they should be so I'm guessing/hoping it is a stability/oscillation problem. Is the best way to test this by removing the input connections? Should I test it with the input shorted at the module?

Simon.

[simple simon]

Originally Posted by Mooly

So is one module working OK ? and drives a speaker OK ? as you say only one develops the offset, yet ask if both can be broken the same way.

Well I have now tired 3 modules with two separate power supplies and two different "arangements" (one in box, other spread out on bench)

All modules nearly always develop a DC offset if a load is attached prior to switch on and series light bulb stays bright. This sounds like a loud hum (not buzz) when I am brave enough to use a loudspeaker.

If nothing is attached across the output then the lamp goes out after being bright for a second and does not come on when the speaker is attached. I can also play music when this happens, but with an infrequent crackle. Eventually after one of these crackles the hum comes back and the light comes on.

Could this be the protection circuit going bad?

I still cant quite accept that all of the modules have died in the same way and that I'm not doing something wrong.

Simon.

[nigelwright7557]

It could be a design fault that makes the amp unstable without a load connected ?

[runebivrin]

Maybe it just needs a Zobel network on the output? You could always try connecting an 8 ohm resistor in series with the speaker to see if that removes the problem. Then it's definitely a stability issue.

[Mooly]

Hi Simon,
It does sound odd that 3 modules all have the same apparent problem... yet on the other hand these things are complete in themselves and apart from a PSU have no other components needed.
You say you have tried 2 PSU's (Are these totally different, everything from mains plug to amp ?) because the only other thing I can think of is perhaps a some PSU issue where one rail doesn't appear correctly or is "slow" to appear at switch on etc and this latches the amp in an unpredicatable state.
And thinking of even weirder stuff, could there be an "ageing" issue within the amps, something like the potting compound stressing or reacting with something over time.

If you can guarantee the PSU's are good then it must be the modules (all three) that have failed in some way. There is nothing else left.