Topic: onkyo stereo amp.

[dave500]

whos into old amp repairs?my dads old onkyo died,the fuse is fine,a little relay clicks inside when its switched on but no lamp or sound at all?i gave him a spare pioneer I had,this is too good to throw out its like 35 years old?shop job I think unless someone can give me a hint at something else obvious to look for?its model A-3100.

[78 k550]

Sorry, can't help.

Paul

[strynboen]

thek transformer at primær and sekundær side....then thek the diode..its a black standing box vith 4 legs..2 for ac and 2 for dc..it have a 45 degrede angel at the one side..
if it are gone ,,just take one from somthing else..it are a common piece of cake..

[BobbyR]

Dave, I used to deal in vintage stereo. If it was a power transistor they usually blow the fuse. Having said that, there are fuses inside the unit so they will blow first.  This unit was more popular in Europe than the US so I had to look at some of my sources.  It is a good looking unit, sadly it has a reputation of not sounding very good.

Having said that, if you want to tinker you can try what Stroyben suggested. Dad may be better off with the Pioneer. You seem to be a straight up guy, so I told you what I discovered about the unit.     

[dave500]

dads into jazz,i always thought it sounded fine?it came as a complete matched system with onkyo cassette deck(the hatch is real glass!),tuner and turntable and speakers,ill open it up again and have a proper dig around,the main fuse is fine and two others are fine,i spotted four diodes standing up proud of the board,ill check the transformers outputs?thanks fellas.

[strynboen]

the diode can be 4 separate or a brigde vith 4 in a  black plasticcasting..

[Killer Canary]

I'm thinking power supply also. Check for heat marks on the board and look for components that have been heat blackened. Check the foil side of the board for burnt foils.

[dave500]

his happy its running again with the pioneer,i pulled it out of a dumpster!runs fine,he uses his stereo a lot,ill fiddle with the other one later but wont throw it out,looking for a schematic online I only found one guy saying they had bad sound?its in the ears of the beholder?heres the pioneer its an A-109.

the flash picked up the dust in the tape deck door,i must clean that for him it unscrews easily,it also has the right hand VU meter lamp is dead.

[Duke McDukiedook]

Like Bobby said blown transistors usually blow the fuses. It could be something as simple as a blown power cap or diodes.

[dave500]

thanks again fellas ill post some inside pictures later,none of the big caps looked buldged?might have to demount a board to look underneath?

[BobbyR]

It's not a bad unit. You have 50Hz power so the models# are different since 50HZ gear is sold in Europe and Asia. The A3100 was not sold in the US.  I had an Onkyo receiver and it was OK. All Japanese units were awesome on the AM Band but weaker on FM. Japan was very late on adopting FM Radio, so they were more familiar with AM. The US brands(when there were some) focused on FM. 

[dave500]

Im getting 40 and 20 volts ac from the transformer,cant see any obvious burnt looking components,those two big caps are the things to fail?

[scottly]

Hey Dave, when those big caps fail they either short (blow up or blow fuses), or dry out and loose capacitance, which will result in a loud 50/60 cycle hum in the output.
Diodes D921 through D924 are most likely a full wave bridge rectifier for the main DC supply. If you have 2 AC voltages from the transformer, I would expect to find 2 DC voltages some where on the circuit board. The real amp is the STK461 device mounted to the heat-sink.

[dave500]

ok ill check those diodes?the transformer has three out put wires,two are the same colour orange,they gave me 40 volts,one is black,this black and any of the other two gives me 20 volts,i had removed them from the posts to test.

[scottly]

Those two big caps should have rectified DC at their terminals, but you would have to lift the board to get to the bottom side. The one shows a 35V rating, so I would expect to see about 20-30V max.

[dave500]

ok ive got the bottom panel off and can see the underside,cant see any dry joints,ill check for dc at those caps,then if none ill remove one leg each of those diodes and check them?

[dave500]

ok ive got 26 volts at both those caps.

[scottly]

Just for grins, switch the digital meter to AC and see what you read.

[dave500]

ok the right hand one has zero and the left 1.2volts ac

[grcamna2]

I'm thinking power supply also. Check for heat marks on the board and look for components that have been heat blackened. Check the foil side of the board for burnt foils.

+1

[dave500]

shall I demount those four diodes and check them?

[scottly]

Naw, sounds like the power supply is OK. That hybrid integrated circuit amp is most likely the culprit?

[dave500]

ok,it has no sound or power lamp though?ill put it all back together and shelve it for now,thanks a lot for your help though everyone!just out of interest heres my sanyo DCA-411 I bought new in about 1980!still sounds great save for scratchy pots,ill clean them next time its out of the cabinet.

[scottly]

Yeah, the power lamp makes me wonder? You mentioned you could hear a relay click when the unit is powered up; this is probably the black cube marked RL901. If it isn't properly switching power, it may be the problem. In any case, I'd also shelve it: I've found better amps for cheap at yard sales.(not as cheap as the bin )

[dave500]

thanks scottly yeah the relay crossed my mind,one or two cruddy contacts,might be a multiple relay inside with one dead circuit?i should've checked power to the lamp it might also have a blown globe there?its a tiny soldered in place unit in a crumbling cardboard tube,maybe another day?thanks again at least we gave it a shot!i did end up unsoldering one leg of each of those diodes,they all checked out ok.