Akai AM U210 repair (beginner). - UK Vintage Radio Repair and Restoration Discussion Forum

kortina · 18th Apr 2017, 1:07 pm

Hi Guys,

I have some fairly basic electronics skills, and I offered to try and fix my father in-law Phil'S amplifier.

Phil dusted off this amp and gave it a massive workout. After more than an hour it let the magic smoke out and gave up.

I opened up the amp and noticed a few things:-

1) the fuse was set in the 220V slot, not 240V. I assume that here in AUS it should have been set at 240V? The amp had worked for 20+ years, but I suspect it had NEVER been driven as hard as last week.

2) The capacitor at C9 had blown the bottom out (50V 10uF).

I replaced the capacitor with a 64V 10uF that I got from my local electronics store.

I turned the amp on and the resister at R5 started to glow, then C7 (50V 10uF) blew the bottom out.

Fair enough to say that I am out of my depth.

I can't read the color code on the resistor at R5, and the photo I took earlier is very hard to tell the colours.

Should I just give up?

http://www.vintageshifi.com/repertoi...-Schematic.pdf

I can easily replace C7, and can also replace R5 but I can't read the schematic.

My guess is that both these components fried because of some other underlying cause, but I have no idea where to start.

Any help would be most appreciated.

Edward Huggins · 18th Apr 2017, 1:37 pm

I suspect the "overdriven" amp has had its power supply put to the test. I would look for distress in the main smoothing (high voltage) caps and the rectifier. These amps are currently selling for about £95 and are worth fixing. The schematic is not that easy to follow.

paulsherwin · 18th Apr 2017, 1:57 pm

Akai were great fans of ICs and this amp is full of them. It's impossible to say what the fault is from the described symptoms, but there's a good chance that the output STK463s have died. This will be a very challenging repair for a beginner, and a commercial repair is unlikely to be economic even accepting Edward's rather optimistic valuation.

Michael Maurice · 18th Apr 2017, 10:02 pm

I agree with Paul. Those STK... IC's were never the most reliable items.

kortina · 19th Apr 2017, 4:09 am

I noticed you can buy the replacement STK online for about $10.

Given the resisters and caps would be another $5 max, would it be worth just trying to replace the lot?

Can anyone decipher the R5 value?

I am comfortable soldering the resisters and caps. The STK looks a little harder because there are so many pins to do at the same time, but I think I could do it.

$15 and an evening sounds like a potentially rewarding challenge. If it fails the kids won't be going hungry.

paulsherwin · 19th Apr 2017, 11:14 am

R5 appears to be a 10 ohm fusible resistor, though I agree that the circuit diagram is difficult to read. A serious fault in the STK module might cause it to burn up.

By all means change the module if you want to and think you're up to it, though I'm concerned about your admitted lack of diagnostic skills. It's your time and money though

18th Apr 2017, 1:07 pm	#1
kortina Retired Dormant Member Join Date: Apr 2017 Location: Canberra, A.C.T, Australia Posts: 2	Akai AM U210 repair (beginner). Hi Guys, I have some fairly basic electronics skills, and I offered to try and fix my father in-law Phil'S amplifier. Phil dusted off this amp and gave it a massive workout. After more than an hour it let the magic smoke out and gave up. I opened up the amp and noticed a few things:- 1) the fuse was set in the 220V slot, not 240V. I assume that here in AUS it should have been set at 240V? The amp had worked for 20+ years, but I suspect it had NEVER been driven as hard as last week. 2) The capacitor at C9 had blown the bottom out (50V 10uF). I replaced the capacitor with a 64V 10uF that I got from my local electronics store. I turned the amp on and the resister at R5 started to glow, then C7 (50V 10uF) blew the bottom out. Fair enough to say that I am out of my depth. I can't read the color code on the resistor at R5, and the photo I took earlier is very hard to tell the colours. Should I just give up? http://www.vintageshifi.com/repertoi...-Schematic.pdf I can easily replace C7, and can also replace R5 but I can't read the schematic. My guess is that both these components fried because of some other underlying cause, but I have no idea where to start. Any help would be most appreciated. Last edited by Station X; 18th Apr 2017 at 1:16 pm. Reason: Bad link deleted.

18th Apr 2017, 1:37 pm	#2
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,340	Re: Akai AM U210 repair (beginner). I suspect the "overdriven" amp has had its power supply put to the test. I would look for distress in the main smoothing (high voltage) caps and the rectifier. These amps are currently selling for about £95 and are worth fixing. The schematic is not that easy to follow. __________________ Edward.

18th Apr 2017, 1:57 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,975	Re: Akai AM U210 repair (beginner). Akai were great fans of ICs and this amp is full of them. It's impossible to say what the fault is from the described symptoms, but there's a good chance that the output STK463s have died. This will be a very challenging repair for a beginner, and a commercial repair is unlikely to be economic even accepting Edward's rather optimistic valuation.

18th Apr 2017, 10:02 pm	#4
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,230	Re: Akai AM U210 repair (beginner). I agree with Paul. Those STK... IC's were never the most reliable items. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

19th Apr 2017, 4:09 am	#5
kortina Retired Dormant Member Join Date: Apr 2017 Location: Canberra, A.C.T, Australia Posts: 2	Re: Akai AM U210 repair (beginner). I noticed you can buy the replacement STK online for about $10. Given the resisters and caps would be another $5 max, would it be worth just trying to replace the lot? Can anyone decipher the R5 value? I am comfortable soldering the resisters and caps. The STK looks a little harder because there are so many pins to do at the same time, but I think I could do it. $15 and an evening sounds like a potentially rewarding challenge. If it fails the kids won't be going hungry.

19th Apr 2017, 11:14 am	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,975	Re: Akai AM U210 repair (beginner). R5 appears to be a 10 ohm fusible resistor, though I agree that the circuit diagram is difficult to read. A serious fault in the STK module might cause it to burn up. By all means change the module if you want to and think you're up to it, though I'm concerned about your admitted lack of diagnostic skills. It's your time and money though