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3000a Questions...

roblebo

roblebo

New Member
Hey everybody - I have been lurking here for a couple of months and am feeling brave enough to try my first post...please forgive me if I have done anything wrong.

I have a number of 60's/70's Sansui receivers and just acquired two more (free!) this weekend. I have been very lucky here in the DC area what with all the retired military folks getting rid of thier stuff. Picked up a 3000a and 5000a both in great cosmetic shape with wood cases. Fired up the 3000a today and gave it a good cleaning and she sounds wonderful with headphones. Can't wait to try it out with my Cornwalls when I get home. The 5000a powers up but no sound-yet.

My question is : There are two lamps on the 3000a to the left of tuner behind the signal meter that are back to back. One has a green plastic bubble around it. The other does not. The green one functions, but I am not getting anything from the one next to it, even when I swap lamps. Does anyone know what this lamp might do? Seems like a weird setup.

Any advice regarding the 3000a (service bulletins/safety issues etc) would be appreciated!
 
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roblebo said:
My question is : There are two lamps on the 3000a to the left of tuner behind the signal meter that are back to back. One has a green plastic bubble around it. The other does not. The green one functions, but I am not getting anything from the one next to it, even when I swap lamps. Does anyone know what this lamp might do? Seems like a weird setup.

Any advice regarding the 3000a (service bulletins/safety issues etc) would be appreciated!
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Welcome to AK. I believe the green bulb should only be on while the AM or FM input is selected. The white bulb comes on when you have a strong signal. I could have the colors reversed. I've had a 3000A since 1977. Built like a tank and sounds sweet.

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Thanks Duffinator (I actually did have a post a few months back and forgot)...That is a beautiful 3000a- mine is in similar condition from original owner who bought it in Japan in '66.

I guess I should have hooked an antenna up because as soon as I did, that whit light came on indicating a strong stereo signal! This thing sounds great- as good or better than my 1000x, 2000x, 4000 etc.

So there is no real tuner dial light then for this unit? Just the power indicator and white stereo/mono green light? It would sure be pretty with a little light behind the glass...
 
Dang! Left 3000a on quietly for about 1/2 hour and came down to check on it - protection light was on and no sound!

Any ideas?
 
Pull the 3000a out of the case, and take off the bottom cover. If your receiver has been retrofitted due to a recall you should see two large black ELNA capacitors towards the rear of the unit.

If you do not see them, then its a bone stock unit. There is a scary failure associated with the bias regulation circuit. The bias regulator diodes can open up and kill the outputs (due to excessive forward bias) If you power it back up and its still in protection, the amp is a goner.

If it powers up, does not go into protection, but has no sound, the rail fuse is probably blown which might have saved the amplifier. Do NOT replace the fuse and power back up if its blown, or you could destroy whatever is still working in the amplifier.

If the amp powers up, does not go into protect and plays again. It could be going into protect for the following reasons:
1. improper speaker load (<4 ohms) or short in wiring
2. overheating. feel the back cover after its been on awhile and see if its warm. It should be cool
3. Excessive bias creep. If the outputs start drawing excessive current the protect will kick in and shut down the amp. Measure the bias current by pulling one of the rail fuses and connecting an amp meter in its place. There should be 80ma.

I restored one of these, and they are an awesome machine. However if they are bone stock, they need quite a bit of restoration and retrofitting in order to be reliable daily drivers.
 
Thanks jpdylon...looks like it is bone stock - two caps in rear are grey Elna. See pic below...

The unit does power back up and play, so I will try what you have suggested (I have an in-law who did electronics repair years ago but there is a language barrier!) The unit did feel a little warm in the rear. Could this be from bias creep? If I can get the bias adjusted, any other suggestions to make it safe?

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You actually have the re-call mod. It just may be an earlier version. In the service bulletins it calls for two large ELNA caps, but they have all been black in the 6 3000a I've worked on.

More than likely the bias circuitry has been upgraded as well. The failure I expressed in the earlier post cost sansui big bucks because this was the first direct-couple design. The output transistors would short due to saturation from excessive bias. Then they would dump the rail voltage right to the speakers, Killing them in a matter of seconds. The protector would not always save the them, so customers would not only have to have the receiver fixed, but they would need new speakers as well. The two caps on the bracket shows that it has been recalled and was either sent back to sansui or an authorized servicer.

The fuses are where to take the bias measurement. I'll get some pictures and setup info from the service manual later today for you. If the back panel is warm, the bias is too high. I would refrain from using the receiver until you get that under control.
 
Great info jpdylon...can't thank you enough. It may have been a very early mod as he told me he bought this new in '66.

I was wondering where I could get that info from the service manual so thanks for that too. I am relieved to see it has been recall-modded...I asked the owner if he had the 3000a or 5000a modded back in the day and he claims he did not, so I guess he doesn't remember. Hopefully the 5000a has been fixed as well - haven't had a chance to open that up.

The 3000a is unplugged and benched!
 
roblebo said:
Great info jpdylon...can't thank you enough. It may have been a very early mod as he told me he bought this new in '66.
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Were these made in 1966? Check your serial number with the sticky in the Sansui forum to read the date of manufacturer. Or post your SN here.
 
I will do that as soon as I get home...there was a serial # label that had apparently fallen off and was stuck on packing tape which was holding power cord wrap. I can only assume it was to the 3000a, so will post asap.
 
OK - the label which I think was on the 3000a is ser. # 228102248 which should make it Oct. 68 yeah? I highly doubt he bought it in '66 then.
 
roblebo said:
OK - the label which I think was on the 3000a is ser. # 228102248 which should make it Oct. 68 yeah? I highly doubt he bought it in '66 then.
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That's what I thought. :yes: Mine is also from 68' and 67 was the first year. There is also a 3000 that were sold at the same time.

I need to check with my uncle (the original owner of mine) to see if mine was ever updated. I'm certain mine has the two caps on the bottom in gray like yours but I don't think it was ever serviced. Maybe later models were updated from the factory???
 
setup adjustments

Here are the setup adjustments for the bias and protector circuit.

If you're going to do the protector setup you'll need a signal generator, dmm, and dummy load. You can use a resistance load or a pair of speakers you don't care about.

I'm more concerned about the bias current, but the protector you can set up if you so desire.
 

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Thanks for taking the time to post those for me Jordan - much appreciated. I will probably just set the bias and leave the protection circuit alone for now, but nice to have if that doesn't help.

this forum is great!

Rob L.
 
indeed!

Jpdylon, sorry if I am showing my relative newbie status here, but in the bias adjustment page, when they refer to connecting a resistor to the speaker output terminals, are they referring to the terminal screws? Any specifics would be great.
 
The speaker output terminals are where you would normally connect a pair of speakers --the exact same place.

It is ok to use a pair of test speakers that have no value to you. The sole purpose is to use a dummy load so that the amplifier bias is set up under normal operating conditions.
 
Jpdylon,

Thanks again for the scans...Just to clarify...the bias adjustment from service manual I assume is done with one multimeter (2 leads) to one fuse holder at a time. The drawing is a little misleading.

So am I correct in assumming VR 803 is for the first fuse holder (R-) and VR 804 is for the second fuse holder (R+) and then , although not printed, the two left fuse holders would be adjusted with VR 805 and VR 806? It is hard to figure out without a schematic, and I hate to buy a service manual when I don't know if I can even keep this unit.
 
Gimmie some time to dif up my service literature. I have board diagrams for the 3000a that will help me to remember how to do it. It's been nearly 2 years since I last opened one up.
 
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