akai AM-52 gives no sound at all

[estate]

Hi, let me first make myself known.

My name is jan and I come from holland, I'm 52 years old and in my early days repaired many ald and broken amps and tv's, but as I have not done such for at least 30 years i have lost the touch and feel.


Now i have bought myself an amp from AKAI, model AM-52 and the bloke I bought ir from said it should work, when coming home I hooked all up and although I hear the relais switching and there should be power on the speakers output I get nothing at all.

Visually i can not see there is anything wrong, no molten components or anything that was too hot is found,a lot of dust yes, but I brushed that out with a pighair brush and that's all.

I found that the shortcuts between the left and right adaptor plugs was missing (as seen on the schematics i downloaded here) and I put them back and still no sound or any messurement.

How can I determine what's wrong with this amp ?

Who can help me any further, I like to get this one going again to use for a small studio I'm making for digitizing my old tapes and records.

Thanks for helping out in advance.

[estate]

sorry, wasn't logged in.

The leds D112 and D112b both are lit green when the amp is switched on, I don't know if this is important to mention but I guess it can help.

I thought that when it was green it was okay and the circuit would work OK.

Anyway, if anyone can help me, please.

[vtech]

Always make sure to leave the main volume set at low level-- just in case you find what may be wrong & prevent damaging the amp. I'll try to help but am not here all the time & need to check back often;

What source are you using? Based on your description, can't be any thing major; if the relays click, more than likely your final stage is ok. You already know about the "shorting plugs" which you have already reconnected.... How about the "tape monitor" switch?

Vtech

[estate]

All switches were set okay, I tested the aux, tape, and phono plugs bot no sound what so ever.

I dismantled the amp and took out the power pcb and saw that the bottom of the pcb was been very hot once (colored brown)

I started to measure and accidentally shorted one of the triacs (but the reading was too high as I discovered)

I am now in the way of ordering all three triacs and the big resistor (tr101, tr 102, tr103, and R 1K 1/2 W and am going to replace them all. ( and try to als get 3 new foil condensors 823J as well )

I read 68 volts at a point where it should be 55 volts so I guess the rebuild of the power print is the most logic first step.

Problem is I don't own me a good scope so i have to do all with a digital mm and that's not always as precise to measure

But even with this faulty power print both green leds stay lit (what is that, why are they even there, what do tey mean, what do they want to say ? )

[estate]

Oh,

I also measured TP1 and TP2 (which should have at least about 20mV after 20 minutes of standby time) and it gave me a null reading 0 volt, when carefully truning VR 101 and VR101b there was no reading, so that's why I started to check the power print.

[estate]

BTW, sorry for beeing so blunt, I totally forgot to thank you for trying to help me out.

[vtech]

Triacs? you meant to say transistors as there is no triac here. Why change them? Sounds like you may have jumped way ahead! Hope you have not inadvertently caused more damage
The proper way to troubleshoot is to first look at all supply voltages and see whats there and what is missing before trying to change parts. You mentioned probe slipping? did it short anything? What/where was the burned mark on the pcb? When powered up, Does it stay in protect mode? (what do you read around IC102?) How about at power supply connectors ? (W101.102.103 etc?)
Tp101, 102 has to do with bias adjustment and you will not read anything if the basic voltages are not present.

[estate]

transistors, it is my bad.

I was measuring the voltages and my probe slipped, the transistor tr103 gave a bit of a high voltage when measured and after the slip it gave just about 9 volts, that's why I want to rebuild the power print, I have inadvertenly broken one of the transistors.

I am not going to put any probe in it again before i buy me a pair of new ones, totally isolated up to the tip.

Today the shop where I buy my parts is open untill 21:00 tonight and I hope they have the parts on stock. ( I mean it are parts that cost around 3 euro each, no blood flowing from that )

On W101, 102, 103 I measured voltages that seem to be okay until after my slip that's why I need new parts (i guess) and certainly new probes well isolated ones.

Around IC102 I did some measures and I started at D111 (AC to DC conv) the measured value was clearly within range so there is power on a part of the pcb, after that I messed up by shorting TR103 (just a short sparkle but a little too much I guess)

TP101, 102 was measured because I had an idea that when there was no power present there i should go way back to the beginning (that was my first measure to see if and how much power there was on the bias to exclude an eventually broken end stage)

[estate]

got me a pair of new probes

Okay measured the transistors 101, 102, and 103 and they seem to be in range, all give about 4,5 K ohm on the MM (my son helped me to explain how to measure this )

I switched the power on and I notice that R105 ( 1K 1/2 W according to scheme) is getting rather hot, the measured temp is about 180 degrees celcius, so I am suspicious about the power it gets.

Although it only is for the power supply of the power led ? i can't imagine this is a good sign.

I am now going to remeasure the points mentioned before and give a listing of the voltages later.

[estate]

PS.

measurements of tr 101, 102, 103 are compared with newly bought parts (as they are not that expensive I bought me some when I was getting me a new pair of probes)