Re: 820-2936-A boardview & schematic please
Hi folks, can anyone tell me if there's any difference between 820-2936-A and 820-2936-B?
A-Billi-Tea
Member
Last Activity: 02-11-2020, 06:33 AM
Joined: 03-05-2018
Location: Melbourne/VIC
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Rotel RA-840 (1960's?)
Has anyone seen this amp and know where I may find service info/schematics? Rotel model RA-840. It looks approx 1960's.
I can't find much information on it. It seems Rotel decided it was a good idea to re-use the same model number in another amplifier in the 80's... Thanks ROTEL!
lol...
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Thanks, kaboom. I might just go for 4148 pairs for both D102 and D103.
I can usually get away with most in-circuit resistance measurements because my multimeter (Fluke 79-II) has pretty low voltage output on resistance mode. I'll lift my legs when I need to
EEV Blog has a good video on this, I don't remember the video number.
C101 is a Tantalum, originally 10μF/10V and I've replaced with a fresh 10μ/16V Tantalum. C107 is an electrolytic 33μ/10V. All of the Aluminium electrolytic...Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Thanks for the tip. I guess I'm getting my V's mixed up lol. I read somewhere that VD-1221 is a Varactor of some sort but that's obviously wrong info? I cannot find the data sheet for it.
Even "Silicon Varistors" are a pain to find, the only Varistors readily available from my usual go-to suppliers (RS, Farnells, Mouser or Digikey) are MOV's which are obviously not what is wanted!
So, do you think 1N4004's will suit better than 1N4148's?
Are you shure I need to replace...Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
I guess the D103 VD-1221's are just picking up the temperature of the air inside the unit!!! Doesn't sound like a great design...
It couldn't be too hard to modify it so that the driver transistors are mounted on the OP transistor heatsink (and both of D103 too). The problem is replacing VD-1221, I don't trust them for long-term reliability.
R_J mentioned NTE601 as a replacement, but they're practically just as obsolete now and way over-priced on eBay.
There must be another substitute/replacement?...Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Hi redwire,
You say "D103 is for bias only and cannot affect offset much". So, I'm thinking why is VR102 (which is SUPPOSED to be for DC OFFSET according to the service manual) directly in series with D103?
Answer = V102 IS NOT FOR DC OFFSET! The service manual is incorrect, V102 is for IDLE ADJUSTMENT and VR101 is for DC OFFSET! Gees thanks Luxman for trolling me lol.
VR101 did appear to in fact affect the Idle Current, so that mislead me a bit!
So basically, my problem...Last edited by A-Billi-Tea; 06-27-2018, 08:08 PM.Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Update: I have tried putting VD-1221's into D102 and D103 of the RIGHT channel but no change!Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Yes, I know. What I am saying is that someone replaced both D102's with dual series 1N4148's and I replaced both D103's with dual series 1N4148's.
Perhaps D102 is a problem with the 1N4148's? I have exactly 2 VD-1221's at my disposal so I guess I can try putting the VD-1221's into D102 an D103 on one channel.
...
Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Thanks RJ, I'll try that next if putting in the proper OP Transistors doesn't work!...Leave a comment:
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Re: Luxman L-80V DC Offset a bit too high ~150mV
Hi rewire, thanks for the suggestions! Woops I forgot to attach the image in the initial post.
1st of all regarding the replacement transistors, I thought the same as you also but I put the originals back in which were still in the RIGHT channel (what I THOUGHT were the originals), 2SD388A/2SB541A and I got the exact same result. Looking more closely at the schematic now I see that they are meant to be 2SD-188A/2SB-545A does look right to you? I didn't see this earlier because I was only looking at the parts list section...Leave a comment:
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Luxman L-80V DC Offset a bit too high ~150mV
Hi all,
I have a Luxman L-80V late 1970's Stereo Integrated Amplifier.
The amplifier appears to work just fine but it is showing 174mV on the LEFT channel speaker terminals and 158mV on the RIGHT speaker terminals.
This is obviously not ideal! It can be better.
This amplifier has a DC Offset adjustment, but my problem is it isn't working!
If I turn the adjustment all the way clockwise it will shave about 10mV (at BEST) off from the DC voltage but the OP transistors get HOT! So of course, I wasn't going to leave it like for more... -
Re: SVI3206D Hybrid IC ( BC POWER MODULE BY SANYO)
I was thinking about this concept recently, it would be excellent to be able to refurbish these STK and SVI IC packages!!!
Can you tell me how you opened the modules? Did you use heat to melt the glue? I have had no success trying so far, but I did get one open by cutting into it with a dremel, but that was a bit messy... :PLeave a comment:
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Re: New Members - please post your introductions here
HELLO FROM MELBOURNE AUSTRALIA!!!
I run a small business from my home in Melbourne fixing consumer and pro audio electronics.
I hope I can find some useful information here and hopefully I can share some of my own wisdom along the way too!!!
Regards, BLeave a comment:
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