Teac AG-H350 No Audio

[Miggi03]

Dear all..

I bagged a Teac AG-H350 off eBay with no audio for 2 reasons. The profile suits my very limited space at home and gives me 5.1 audio and also to save something else hitting the landfill!

As the title goes there is no audio output of any kind. No matter, the volume input type through either speakers or headphones.

I have had a search around Google and the various forums I frequent but turned up nothing on this type of unit. It's an odd sandwiched PCB, few ribbon cables that all check out ok but from 2002 so mainly through hole components.

I have tested, the relays, they all click into position and respond to input selection either making or breaking the connection as they should and checked for bulged or blown capacitors and all 3 fuses are intact however they are on the 230v rail so of no use.

Before I get into a tear down is there anything very basic troubleshooting steps anyone could recommend or anyone else had experience this type of unit? I'm still fairly new to this but loving the whole salvaging and reusing thing at the moment.

Thank you for the read and any input.

[tri-comp]

I haven't had any experience with this exact unit but I've had some experience with similar electronic input switching circuits.
Signals from all sources, including the tuner-section, are routed through the TC9164AF switch-array, see page 13, upper-left.
I've had this exact integrated circuit fail in several sets of different brands.
Some times they may quit entirely and pass no sound, possibly intermittent. Some times they cause distortion to the routed signal.
In some cases, when the fault is permanent you MAY be able to provoke a reaction from the chip by hitting it with a spray of freeze-mist, see:
https://www.145.aero/G-C-Electronics...19-8410-10.htm
or similar.
If normal or distorted sound appears after the spraying you should replace the IC with the EXACT same typeno. as printed on the IC !
Data-sheet for the IC here:
http://pdf.dzsc.com/TC9/TC9164AF.pdf

Best regards and wishes for a Merry Christmas,

/Torben

[Miggi03]

Torben, thank you so very much for this information. I will give it a go after Christmas and post my findings here should anyone else have this type of unit. May help down the line.

Have a great Christmas.

Michael.

[Miggi03]

Hi, I replaced the switch-array as suggested but this made no difference. It was a TC9163AF in this unit. Shame I was really hoping to get this working. Whilst I had it open I realized I have reached the limits of my knowledge on this. So many IC's...

Thank you all the same. I am still open to any suggestions on this unit.

[PJL]

I guess you have checked all the power rails?

This has 5 separate discrete power amplifiers with over-current protection that is consolidated into a single 'protector' signal. There are also various relays that connect the speakers to the amplifiers. Are these the relays you have already checked and they are working correctly?

It must be possible to chase through a signal and see where it gets lost. There is some kind of mute control, have you tried following that through?

Are the lamps behaving?

[Miggi03]

Originally Posted by PJL

I guess you have checked all the power rails?
Yes, perfectly adequate.

This has 5 separate discrete power amplifiers with over-current protection that is consolidated into a single 'protector' signal. There are also various relays that connect the speakers to the amplifiers. Are these the relays you have already checked and they are working correctly?

I have, there is a Protection mode but it never becomes active. Switching between Surround and Stereo makes the relays become active/inactive as they should.

It must be possible to chase through a signal and see where it gets lost. There is some kind of mute control, have you tried following that through?

No not yet. I have one of these DSO150 kits that I assembled. Could this be enough to get me through this test? If so is it a case of tracing an inputs singal line as far as the point of failure?

Are the lamps behaving?

Sorry, as in the input selection lamps? Or the display itself? If so, yes to both

Thank you.

[PJL]

A DSO150 would be perfect, a PC can be used as a signal source using one of the free audio siggen programs.
Have you tried the test tone?
Does the radio appear to work?
Have you tried connecting the REC audio outputs to another amp?

[ms660]

Just an observation so far as I can make out, it looks like the mute output from the u-COM IC (IC75) ends up on pin 11 on CN73 to mute the input to the amplifiers.

High for mute by the looks of it.

Lawrence.

[Miggi03]

Originally Posted by PJL

A DSO150 would be perfect, a PC can be used as a signal source using one of the free audio siggen programs.
Have you tried the test tone?
Does the radio appear to work?
Have you tried connecting the REC audio outputs to another amp?

No to all but these are next on my list. Thank you so much.

[Miggi03]

Originally Posted by ms660

Just an observation so far as I can make out, it looks like the mute output from the u-COM IC (IC75) ends up on pin 11 on CN73 to mute the input to the amplifiers.

High for mute by the looks of it.

Lawrence.

Forgive me Lawrence. Could you kindly elaborate on this? I'm not sure mute comes into play as the VFD has a section for "Muting" this isn't displayed. I am however as you've all probably worked out very new to all of this. I do really appreciate all your replies.

[ms660]

PJL mentioned some kind of mute circuit in it, I happened to look at the schematic and found a mute signal output from the u-COM IC (IC75) it ends up on pin 11 of connector CN73, it appears to me that if the voltage at that point is high and not low then all the inputs to the amplifiers will in effect be connected to ground, that would mean no output.

As to whether or not the mute circuit is causing the problem who can say, usually in the case of no sound the first check apart from operator error etc would be to check the power supply rails, however if you wanted to check the mute circuit you should now be able to follow it through from the IC to the muting transistors.

Lawrence.

[PJL]

The User Manual is available FOC online. You should go through the setup where you will also find the test tone option. The setup also allows you to configure the available speakers.

[Diabolical Artificer]

The service manual has a block diagram, so what you do is put in a 1khz sinewave and go through the whole amp from left to right checking that every triangle (which is a shorthand for an amplifier) has an output on the apex of the triangle on the RHS.

This means cross referencing from the block diagram to the schematic to find the triangles in reality, not easy. It may also mean searching for transistor and IC datasheets online to find out which pins/legs are which.

One thing though, looking at the service manual I note there are lots of boards each with interconnects, check them first by powering said amp up, then poking about with a stick, prefably a non conductive one : )

This is why I love valve amps, there is only usually three or four active devices compared to the chaotic profusion of insane IC's and mad transistors with no standard pinouts found in SS amps. Just saying : )

Andy.

[PJL]

Do the test tone first as it will eliminate the input circuitry.

[Miggi03]

That's a very good idea. Eliminates at least 2 of the PCB's.

Thanks everyone for all your responses. I have a clear idea on how to proceed. Just need the time now which I will get on with this Thursday.

[Miggi03]

I finally got round to this and what I have realized is the 8A fuses have been blowing each time I've replaced them. "Twice" So. This has actually been the problem since day 1. Kind of making all of the above redundant.

I have spent my time trying to trace a likely dead short. I have come to this conclusion only because they are 8A fuses which is huge so something significant is wrong here.

I'll let the pictures explain here but PSU.PNG these are the fuses that blow. Immediately upon powering up. However only when the boards mentioned are tested. The PSU does not blow these fuses with nothing connected.

In AG-H350 this is where I have begun tracing the short. When I connect up the boards which I have colored 12v traces in red. I have tested these out of circuit OK. How I "believe" I know I have a dead short and again my belief is when the board in the middle is connected to the board on the left. A dead short appears between GND - Any pins. And the 12v Rail. Execpt now I've run out of things to test because I myself have run out of knowledge. I have placed a ? where my ideas end because of a lack of understanding going forwards...

Any suggestions would be appreciated. Hope you are all keeping well in these troubled times.

[Michael Maurice]

What happens if you keep the power supply board KUP11466 connected but with connector WF53 removed?

If the fuses blow again, then I would suspect the bridge rectifier D517 has failed.

[Miggi03]

Hiya one of the fuses blew immediately upon powering it on. WF53 removed.

KBU804F is what the manual references and this somewhat confirmed on the part as it has just 804 on it.

Is this ok to replace it with?

https://www.ebay.co.uk/itm/201605203575

[Michael Maurice]

Yes it is. Remove it and check for shorts between each leg,.

[Miggi03]

Yes it's certainly shorted. Can I ask how you got to that conclusion so fast? If you have time to explain. I looked at my troubleshooting method and realised it would have taken me forever to get there.