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Old 5th March 2007, 09:02 AM   #1
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Default Advice on fixing an old amp that has just stopped working

For a long time I've been using an old Akai integrated amp. It's quite decent, and has been around about 20 years. I was surprised to find that it is slightly better than a more recent NAD except in the bass. It has a more relaxed sound which I prefer. While it is an integrated amp, it has pre outs and amp inputs. I use it as a power amp.

Today it just stopped working. NO sparks, no flames, no signs of anything. The music just stopped, while my subs kept going. What I notice is that the relay no longer activates when switched on. Could it be that just the relay has failed?

I'm going to open it up and have a look, but in the meantime, can anyone make any suggestions as to how to approach this one?

If I find the relay is faulty and replace it, is there anything else to be wary of? Should I take any particular precautions (apart from not touching charged up PS caps)?

Photos:

Click the image to open in full size.

There is just one relay (that I can see). It has a transparent case and is just left of the 2 PS caps.

My understanding of the layout:

1. Bottom left - input switch and then preamp
2. Bottom right half = input selection switches
3. Middle - PS caps, relay (soft start circuit), there are 2 "chips" or transistors, one large and mounted to the heatsink, the other just standing and to the right.
4. Transformer and fuses back left and inputs back right
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Old 5th March 2007, 11:21 AM   #2
sek is offline sek  Germany
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Hi Paul,

the relais is of course part of a protection circuit. It's not a soft start unit, it's most likely a DC and turn-on thump protection. Like with a fuse, it doesn't act (or stops acting) without reason. It might be the relais' age and wear, but it could likely also be a fault in the amp that makes the protection circuitry, well, protect the speakers.

The amp module on the right is a preamp part, the module on the heatsink is your power amplifier stage, a so called hybrid module (because it contains both integrated and discrete parts inside). It's likely made by Toshiba, Sharp or Hitachi, as those are widespread and have been the flavour of the manufacturers back in these days.

Those hybrid modules also occasionally fail, and they become harder to get year by year...

A schematic diagram would be helpful, as would be a multimeter and - preferrably - a scope (DSO/CRO). Please be aware that life mains power is present inside the enclosure. Only fiddle with it if you can resort to safety practice a service technician would have. If you're unsure, a service guy can most likely check and repair the unit for an acceptable expense.

With a multimeter, your first approach (before getting a schematc diagram) could be to check the fuses, transformer, power supply and the relais operation. If the circuit has a good voltage supply but the relais doesn't get power, then this would indicate a protective state, as the relais only gets powered as long as everything is alright with the hybrid amp module and the supply power.

Hope this helps,
Sebastian.

PS: Just seen your website. Your Vifa TLs with the passive crossovers might be a tough load on the hybrid module. Those amps are mostly specified for 4Ohms and higher, while such a TL alignment can have dips considerably lower. As you haven't specified any more details about your speakers, you probably don't know their impdance...
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Old 6th March 2007, 05:39 AM   #3
djk is offline djk
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Check for DC on the input of the speaker relay.

Looks like an output like the STK 1050 (1070) and an input like the STK 3062 (3082). If there is DC on the input to the relay, one or both of these may be blown.
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