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Sansui AU 4400 Problems, help/advise needed

dedmonson

dedmonson

New Member
Blowing fuse F02 on main and power supply circuit board. Suspect the Right channel transistors TR14 and TR16 are bad. TR15 and TR13 were replaced at some time in amps long history with some non-original transistor. Replacement 2SC1444 are difficult to find and expensive. Have been led to believe 2SC1445's are good replacement ??? My Questions are as follows:

1 Is the 2SC1444 my most likely point of failure in right channel?
2 If not the C1444 what else could be blowing my fuse?
3 What would actually be the best direct replacement for the S1444 if not the 1445?
4 can anyone supply a restored/NOS F2402 card or restore the card I have?

Thanks in advance for your help/advise
 
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Hi, yes start at the outputs (6 way diode test) and work your way back, the drivers and pre drivers are also likely damaged and possibly some resistors/diodes. Don't bother trying to source those obsolete TO-66 output devices, you will likely only find fakes. TO-220's can be retrofitted just as easily with the centre leg cut off.
 
Thanks so much for your help. Whether you're a working technician or a busy hobbyist I know your time is valuable and I appreciate your generosity. I was in Sydney in the late 70's with US Navy and still recall the generosity and hospitality of our Australian hosts. I am awaiting 4 NOS Sanken 2SC1445's that I bought on e-bay. They are identical to the S1444 in every way except that the collector-emitter voltage and the collector-base voltage differ. Below is a copy/paste from another inquiry that will give some history of the amp.

TR13 and TR15 were replaced (with ECG196's) years ago with very non-original transistors by local technician. when amp failed again I just put it away. drug it out the other day hoping I might find something obvious. schematic shows 2 internal fuses. both were blown. I replaced them and it did power up and work, but there is no right channel. Right fuse blew twice and that was the end of my repair efforts.

let me further say that I am not a trained technician. I am a DIY guy with some electrical and instrumentation training and experience. I am comfortable replacing the 4 output tr's but beyond that I'll be tempted to abandon the project for fear of ruining amp. Will install the S1445's and hope for the best. If your generosity extends further I'm certainly willing to give it a try. My test equipment is limited to a good fluke meter that does have cap and diode functions. I also have schematic and basic repair manual that I downloaded
 
Your very welcome. Nice to hear the Aussies looked after you back in the late 70's :thumbsup:. Yes, those 2SC1445's will work fine, as you say they just have a little more voltage headroom.

I just looked at the schematic, doesn't fuse F02 feed TR13 and TR15? You will have to check emitter resistors R41 and R43 (0.33 ohms) and TR09 and TR11 at a bare minimum. If TR09 and TR11 are faulty then work back and check TR05 and TR07. Personally l would replace 09 and 11 straight up anyway as if the outputs are shorted these drivers will have been stressed even if they test o.k.

Please do not fit your new outputs without checking these other parts as it is very likely you will destroy your new parts also :(. Also don't forget new mica insulators and thermal compound when it comes time for those new outputs. If it was an amp l was working on l would check every transistor in that faulty channel but we will start with the above and see how we go.

You can use your multi meter on diode function to test transistors out of circuit. Here is a link, if you have any questions please feel free to ask.

https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/
Post No.11 has an excellent diagram and explanation of testing bipolar transistors.
 
From the best I can tell, F01 feeds the left channel (odd numbered components) and F02 feeds the right channel (even numbered components). R42 and 44 have been checked and ohm correct, in circuit. TR10 and 12 are on my suspect list. are you also suggesting I replace TR6 and 8 if TR 10 and 12 are bad? I have 59 VDC at the feed end of both fuses so I'm left to think my power supply is good. I have ordered thermal compound but must confess ignorance about what mica insulators are. If I make a pigs ear out of this amp maybe I can hire you to rebuild this F-2402 card for me !!! Thanks again for your kind help and direction/instruction. I just checked the schematic again before posting my reply and find that the schematic in the service manual differs from the full schematic. F01 and 02 are reversed on the full schematic. Multiple examples in the service manual lead me to believe that F02 does indeed feed the right channel (even numbered components). maybe you can resolve this for me ???
 
Thanks Oldsansui441 for your patient help. Just wanted to add that I did research mica insulators and have ordered the correct ones. Still confused about the schematic differences and feel driven to figure it out !!!! Thinking that I may label, pull and test the output TR's while I wait for delivery of the new ones ??? Even though I'm old and retired I still struggle for a free few hours to get something done. Don't know how I ever found time to work a full-time job !!!
 
Indeed, it does look like F02 supplies TR14 and TR16, l was going off the schematic only sorry, not sure why it is different. Have you actually checked the outputs to confirm 14 and 16 are shorted? Nice one on already checking R42 and R44. Yes, if TR10 and TR12 are bad then replace TR06 and TR08, if you need me to cross reference any of these transistors to new parts for you just let me know.

It does sound like your power supply will be fine albeit slightly high, is your unit a multi voltage version or a set US voltage unit? The mica insulators go between the output transistors and the heat sink, you will be fine with re using the old ones so long as they have no cracks or damage, just clean up and apply new paste.

mica-insulators-250x250.jpg


I would be more than happy to rebuild the amp board for you but l think with postage costs these days it would be much more beneficial to have someone locally do it for you, should that become necessary.
 
To Oldsansui441: TR9/10 and TR11/12 proved almost as difficult as the 2SC1444 to find. E-bay came through again. 2SC1211 coming from UK and NOS 2SA697 more
local.
 
dedmonson said:
TR9/10 and TR11/12 proved almost as difficult as the 2SC1444 to find. E-bay came through again. 2SC1211 coming from UK and NOS 2SA697 more
local.
Click to expand...

Not to put a dampener on proceedings but l really hope those transistors off Ebay and the others locally are ok. You see these transistors have been obsolete for many years (prob decades in some cases) and the Chinese have a tendency to either make cheap copies or simply silkscreen the original number onto another totally different transistor and pass it off as genuine :(. I have only ever bought one transistor off Ebay out of necessity and it was ok, apart from this l always buy transistors from reputable sources like Mouser or Element 14 (Farnell). This is why we would normally cross reference old transistors to current production substitutes, takes a little researching sometimes but worth the effort.

dedmonson said:
your kindness and generosity astounds me !!! AU 4400 is multi voltage unit set to 117VAC.
Click to expand...

Your very kind, i'm happy to help and it is no prob whatsoever. What goes around comes around, l have received plenty of help off other members here over the time. Yes your voltage selector is set correctly then, 117v is as close to your wall voltage of 120v as you are going to get :thumbsup:. BTW l like you new profile photo.
 
Pulled all the old output TR's at the end of the day yesterday and will test them today sometime. Have accepted the risk of non-authentic TR's but hadn't considered that they might have totally wrong characteristics/specs. Thanks for the warning and it will impact any future purchase.
 
Thanks for chiming-in Hyperion !!!! Appreciate the added interest.
  • Oldsansui441, have just finished testing the output TR's following the link you sent. Thanks !!! I read, re-read, tested and re-tested and all 4 TR's read good. (the original 2SC1444's on the right channel as well as the ECG196's for left channel. I'm relieved/confused and will spend some more time with the schematic looking to blame some other misfortunate component. Having fun still.
 
Hyperion said:
Wise words and good advice from Oldsansui441. :thumbsup:
Click to expand...

Thanks Hyperion, very kind of you. Thank you also for dropping in as dedmonson has already mentioned.

dedmonson said:
Thanks for chiming-in Hyperion !!!! Appreciate the added interest.
  • Oldsansui441, have just finished testing the output TR's following the link you sent. Thanks !!! I read, re-read, tested and re-tested and all 4 TR's read good. (the original 2SC1444's on the right channel as well as the ECG196's for left channel. I'm relieved/confused and will spend some more time with the schematic looking to blame some other misfortunate component. Having fun still.
Click to expand...

Very interesting indeed. Is there a small chance one of the outputs on that channel was not fully insulated from the heatsink? Were your speakers still connected and the speaker switch engaged when this fuse blew?

Yes good idea to keep testing so as to rule out the preceding transistors in that channel.
 
Oldsansui441: Spent a few minutes with the schematic and wondering if I should I add TR06 to my suspect list along with TR10 and 12? I have no real science to my suspicion but because of their location, I wonder about C14 and 16 ???
 
I did consider a short on the heat sink once the tr's metered ok but cant be sure. would it be safe to fuse the board and power it w/o the output TR's installed to see if the fuse holds? Yes, the speakers were connected, I'm sure. And yes, I'm still having fun !!!:beerchug:
 
Yes also check TR06, 08, 10 and 12. Those caps could also be checked for sure although not as likely being at fault. If your speakers were still connected prob a very good idea to also rule them out as the fuse may have actually done it's job if there is a problem with one of your speakers. Just connect your ohm meter across the speaker wires, should be somewhere between 4.5 and 7.5 ohms, if it was shorted it would read the same as meter leads touching each other. Also make sure the speaker wire insulation is intact and hasn't intermittently touched the two wires.

After checking the above mentioned transistors and the speakers you should be safe to replace fuse and power on without the output transistors fitted, just don't have any load connected, ie headphones or speakers. A better idea would be to use a dim bulb tester and use a 50w globe to limit current flow through the unit. But the worst that will happen is on wall power it might damage more components on that channel if the previous fault hasn't been rectified, you may also be lucky and just have it blow the fuse again.

Glad to hear you are still having fun, that is the most important thing ;).
 
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