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Old 12th November 2012, 01:41 PM   #1
allears is offline allears  United Kingdom
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Default Sansui 9090 help

I'm trying to resurrect a Sansui 9090 , and am having trouble with the Amp Driver board. One channel trips the protector relay , so I'm leaving that one disconnected for now , the other works fine for a few seconds then becomes increasingly distorted . The DC control pot VR01 wants to be turned further clockwise than it will go , and the transistor TR05 gets very hot. Fusible resistor R29 gets fried if I leave it on any length of time. (It should be 390 R , I'm using 2.2K and 470R in parallel , is this ok for fusible?)
Any ideas as to what I should be looking at? The other thing I notice is that in the input from the power board to the driver board (and measuring without the driver board inserted), pins 3 and 16 are at 4 volts and 7 volts respectively , is this ok?
I thought about simply replacing the various transistors but having spent a lot of time on Google I find I'm faced with buying expensive originals on eBay because equivalents are so hard to track down. Has anybody made a list of substitutes for these old transistors anywhere?
Many questions , but I'm learning on the job here. Also , my multimeter continuity/diode test doesn't seem to work for some transistors , and I'm wondering if that is because it's cheap , has too high an impedance or just how things are.
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Old 12th November 2012, 06:05 PM   #2
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I'm sure you will receive lots of replies since everyone has the schematics.
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Old 12th November 2012, 06:36 PM   #3
Mooly is offline Mooly  United Kingdom
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Are you checking the transistors out of circuit with this multimeter ? Are you using the diode range ?

I'm sure all the semiconductors will be replaceable with common generic types but as has been mentioned, without a circuit we are clueless
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Old 12th November 2012, 06:37 PM   #4
allears is offline allears  United Kingdom
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Default Sansui

Yes , I suppose I'm assuming that those who are familiar with this receiver and have worked on it will have the schematic . Happy to hear from anyone else who wants to have a look , so here it is.
Attached Images
File Type: jpg Power Board :Driver Board.jpg (334.0 KB, 110 views)
File Type: jpg Power Supply : Driver Amp.jpg (193.7 KB, 112 views)
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Old 12th November 2012, 06:54 PM   #5
Mooly is offline Mooly  United Kingdom
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I'll try and have a closer look tomorrow if your stuck.

The diagrams a bit small to work too but the amp itself looks pretty conventional.
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Old 12th November 2012, 07:39 PM   #6
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Thanks , I'll try attaching a pdf instead . Sorry it's the whole thing , I can't seem to find a way to save single pages in pdf format. The schematics are on pages 25 and 22 , and the Driver board on page 16.
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Old 12th November 2012, 08:07 PM   #7
allears is offline allears  United Kingdom
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Cracked the single page pdf I hope , the whole thing was too big.
Attached Files
File Type: pdf Power Board and Driver board schematic.pdf (100.1 KB, 39 views)
File Type: pdf Sansui Schematic.pdf (106.7 KB, 35 views)
File Type: pdf Driver board info.pdf (181.4 KB, 31 views)
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Old 13th November 2012, 07:10 AM   #8
Mooly is offline Mooly  United Kingdom
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OK...

The circuit is conventional (a quasi complementary) but one possible problem could be the driver transistors if these are faulty because they are a T066 package which is obsolete today. It may be possible to mount T0126 types with a bit of ingenuity. That is if they are faulty... they may not be. Suitable types spec wise would be MJE340/350.

TR5 and TR9 I can't find much on. These could be suspect too and I say that just based on experience that Japanese devices of this era in these type of packages inexplicably have problems as they age. Again I would say the MJE340/350 would be suitable here too.

For faultfinding I would apply a short across the vbe multipliers collector and emitter (TR07) as that will force the output stage to draw no current. The amp will still all work normally as long as nothing else is faulty.

You need to do a check of all the low value resistors that could have been damaged. The diode VD1212 in the constant current sink is an odd one. I suspect it will be two or three diodes in series in the one package. Thats something to check, that the current sink is working and the voltage across R37 is constant. Exact value depends on the voltage across the diode.
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Old 13th November 2012, 10:00 PM   #9
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Thanks , I'll probably replace the VD1212 , they seem to have a reputation for instability-two 1N4148 in series seems to be the equivalent , I'll post again if I have any great success or get stuck.
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Old 14th November 2012, 11:19 AM   #10
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Here's another pic , a schematic showing the transistor setup. The one ringed in red is overheating , the resistor ringed in red is the fusible one that keeps blowing.
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File Type: jpg audio.jpg (100.8 KB, 54 views)
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