Help with diagnosis of Technics SU-V90D problem

[RetroTechnics]

Hi all,

I wonder if anyone here can help me fix my old Technics SU-V90D.. Its such a cool amp and i'd hate to have to bin it.

I used it to power two car subs at 4ohms each and it worked fine for years. Then it gave up on me one day, worked for a few days after that but now i get no sound at all. I figured i had blown it somehow..

I thought maybe the speakers ohms might not have been suitable for the amp but it clearly states its good for 4-16ohms.

Anyone got any ideas of what I can do to try and fix it, or at least diagnose what happened to it.

I miss my bass so much

[Tekko]

Does the output dc protect relay click approx 5-10 seconds are power on ?

Does the unit even light up or is it as dead as a rock ?

If it power up but doesent pull the dc protect relay, its likely that the output transistors have gone short.

Home amplifiers doesent really have big enough heatsinks to run subwoofers as these tend to take alot more power than a average fullrange speaker.

Do not attemt to power ut up!!! You may cause more damage, making it even harder/more expensive to repair, for each attemt you blow your way toward the input stage.

[RetroTechnics]

Hi and thanks for the quick reply.

Yes the unit does light up but I can't remember if the dc power relay clicks on after a few seconds.. I know what you mean but its not with me right now so I cant check. Its been in my closet since it died last year.

If i shouldn't attempt to power it up, how can i check if the power relay clicks?

[Tekko]

Desolder the output transistors and put an ohm meter to them, if you get 0.00 ohms between any of the pins in either direction, their dead.

Also check for components that look like they've gotten hot.


If the output transistors are dead, then the driver transistors are likely dead too, maybe also the stage before these.

[RetroTechnics]

Okay... well i don't have an ohms meter but i'll try and get my hands on one soon.

Just for the record.. Could this have anything to do with me changing the wiring from in series to independent. I originally had the 2 (4ohm) speakers wired in series giving me 8ohms, which worked for years. Then I made new boxes for them and wired them independently. i.e. 4ohms each channel.

Wondering if I rewire them back to 8ohms , would it make any difference??

Thanks

[Tekko]

Its very possible the amp couldent handle 4 ohms and blew up.

Why not get a dedicated subwoofer amp for the subs ?

[digits]

sometimes the relays themselves die, it can be tested easily by applying a suitable voltage to the right pins after desoldering.

[sakis]

Sorry to say but troubleshooting is about procedure ...then again will require some basic skills ... obviously you dont seem to have them ...

can you read a schematic ??? that can be one start
then you have to follow procedure
as about a few posts ago .... outputs do not fall out of the blue ... so cheking the basics before removing the outputs will be a better thing to do ...

basics mean to verify all voltages here and there before touching anything else ...

let us know how it goes

kind regards sakis

[RetroTechnics]

Fair point about the skill level but i'd still like to give it a shot.

Today I dug it out of the closet & powered it up. It doesn't seem to be as dead as I thought.. Lights on, Relay clicks after 5-10secs...
I tried all the different inputs on the back and most give a very crackly sound and very little volume.
It does however work pretty good with 'Power Amp Direct' inputs but this seems to lose any control of the Bass/Treble/Balance.. From what I remember about the amp, it had both a pre-amp & power amp built into one unit..
Is anyone familiar with this type of setting on amps?

[Tekko]

It's common on higher quality units to allow users to either get a line out after the volume control or the ability to use a separate preamp.

Even my old Telefunken amp from the 80's have pre out/power in