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F-2980 Questions on Sansui G-7500

tinkerer

tinkerer

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Attempting to repair and clean up the mess left by other repair attempts on a G-7500 by unknown individuals, and have a couple questions about the F-2980 board. I am attaching a photo of 2 resistors attached to the foil side of the F-2980 board and am wondering if these belong on the board or have been added by other repair attempts.

#1 is a 22k Ohm resistor across C622 capacitor. Capacitor is 220uF 10v.

#2 is a 6.8k Ohm resistor from Zenor Diode ZD601 Cathode and Ground.

They appear to have been added for some reason, and I cannot find any reference to them in the schematic.

Appreciate any insight and help. F-2980 Edit _LI.jpg IMG_5250.JPG IMG_5251.JPG IMG_5252.JPG
 
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tinkerer said:
Attempting to repair and clean up the mess left by other repair attempts on a G-7500 by unknown individuals, and have a couple questions about the F-2980 board. I am attaching a photo of 2 resistors attached to the foil side of the F-2980 board and am wondering if these belong on the board or have been added by other repair attempts.

#1 is a 22k Ohm resistor across C622 capacitor. Capacitor is 220uF 10v.

#2 is a 6.8k Ohm resistor from Zenor Diode ZD601 Cathode and Ground.

They appear to have been added for some reason, and I cannot find any reference to them in the schematic.

Appreciate any insight and help. View attachment 2360016 View attachment 2360019 View attachment 2360021 View attachment 2360025
Click to expand...
Nope, they do not belong there. Not installed by factory.
 
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Looks like someone was having some issues with the protection circuit. :idea: I can't see what the intention was with those components added in the positions you gave. :dunno:
 
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Appreciate the input.
I have removed the 2 resistors, but still have other issues to resolve.

When powered up on DBT looks like having your turn signal on....bright-dim....bright-dim....bright-dim...etc
 
tinkerer said:
Appreciate the input.
I have removed the 2 resistors, but still have other issues to resolve.

When powered up on DBT looks like having your turn signal on....bright-dim....bright-dim....bright-dim...etc
Click to expand...
Given the random components added, and the fact that the F2980 is an incredibly temperamental beast, I would be going right through the whole thing from beginning to end before even considering applying power to it.
 
Going back through the F2980 step by step checking everything. I had previously rebuilt the power supply, repaired some damaged traces, had blown outputs in right channel, burnt transistors. I suspect the 2SC2581 and 2SA1106 outputs I had in my parts stash are Chinese fakes. The outputs check good using the 6-way diode test but act wonky when installed. I have ordered ON-Semi MJL3281AG & MJL1302AG for output replacements. The Bias and DC 0V pots have been replaced. I've put in a boat load of time on this already, hopefully I'll get it squared away soon, my patience is wearing thin.
 
tinkerer said:
Going back through the F2980 step by step checking everything. I had previously rebuilt the power supply, repaired some damaged traces, had blown outputs in right channel, burnt transistors. I suspect the 2SC2581 and 2SA1106 outputs I had in my parts stash are Chinese fakes. The outputs check good using the 6-way diode test but act wonky when installed. I have ordered ON-Semi MJL3281AG & MJL1302AG for output replacements. The Bias and DC 0V pots have been replaced. I've put in a boat load of time on this already, hopefully I'll get it squared away soon, my patience is wearing thin.
Click to expand...
You need to get the NJL as these are the TO-3P, the MJL are TO-247, the case size is too big to fit this amp.
 
Will 2SC3263 and 2SA1294 also work?
Seems I've noted those as a cross as well from a post I've read.
But...I suspect they are obsolete as well and only fakes are available.
 
tinkerer said:
Will 2SC3263 and 2SA1294 also work?
Seems I've noted those as a cross as well from a post I've read.
But...I suspect they are obsolete as well and only fakes are available.
Click to expand...
No, the 2SC is very high ft, around 60mhz from memory, so might make the amp unstable, the MJL/NJL is the ideal replacement.
TO3P's are very common, you wont have any trouble finding a suitable replacement, but if you have already ordered the MJL's they do have the same Pin spacing as the NJL, you just might have trouble with the actual physical size and where the hole is to mount it.
Just have a look when they turn up, I can't remember the details of the mounting in the G7500, but there might be a way to make 'em fit........
 
Looking at the specs for NJL3281 and NJL1302 at Mouser. I can't see those working at all. TO-264, 5 Lead, 340AA Case, Style 1. No way to make a 5 Lead work on the G-7500.
 
I have discovered NJW1302G and NJW3281G is what I need, but so far I haven't been able to find them in stock.
 
Thanks GrisPato very useful info..
2SA1106 is replaced by 2SA1695 and 2SC2581 is replaced by 2SC4468
 
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tinkerer said:
I have discovered NJW1302G and NJW3281G is what I need, but so far I haven't been able to find them in stock.
Click to expand...
My apologies, I made a mistake I meant NJW but my brain typed the wrong thing.

You can also get the Sanken's if you feel, but the NJW will work extremely well.

However, if you do have the MJL there do investigate if there is enough room to accommodate them....
 
No worries kevzep.
I did get the MJL in and they are too big for sure. The NJW are coming.
Thanks for your help.IMG_5269[1].JPG
 
tinkerer said:
No worries kevzep.
I did get the MJL in and they are too big for sure. The NJW are coming.
Thanks for your help.View attachment 2367329
Click to expand...
Yeah thats a bummer, I can't remember the mounting for those, but is there not enough room to get them in?
Perhaps drilling another hole and hopefully enough clearance either side. Just a thought....
 
Here's a couple pics showing the normal outputs 2SC2581 // 2SA1106 vs the MJL outputs. Probably not impossible to make the MJL fit but to me I'd rather just do the correct T03P outputs. If you look close at the pic of the MJL you can see where the pins would need to go thru the circuit board. Would require some creative bending of the pins. IMG_5276[1].JPG IMG_5278[1].JPG
 
tinkerer said:
Here's a couple pics showing the normal outputs 2SC2581 // 2SA1106 vs the MJL outputs. Probably not impossible to make the MJL fit but to me I'd rather just do the correct T03P outputs. If you look close at the pic of the MJL you can see where the pins would need to go thru the circuit board. Would require some creative bending of the pins. View attachment 2368097 View attachment 2368098
Click to expand...
I reckon they would fit nicely, better devices for heat dissipation than the TO3P. A 90˚ bend on those pins is totally fine...you have them there already....
If I was doing the job, I'd fit those devices, they're not going to look stupid or out of place, but of course up to you.
 
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