Sansui BA-3000 First steps for unknown history?

[audiolab1]

Hello AKers,

I just picked up a BA-3000 at a local estate auction. I did not get it for peanuts, but did snag it for far less than units in poorer cosmetic condition with no refurb work tend to go for, at least from what I have been able to gather. Although I was able to examine the cosmetic condition of the unit before bidding, testing operation was not possible. This might be a good thing as I have no idea of when the amp was last in use and a sudden "plug in and power on" could have been very bad. Cosmetically I would say it is in excellent shape given that it's been around for nearly 42 years. I have attached photos showing it in exactly the state I received it in. I have not even given it a wipe-down or dusting yet as I'd like to know the best methods for cleaning the various parts of the amp. In particular I want to use something that will not harm or damage the silk screened lettering. Any ideas? From inspecting the panel screws it does not look to me that anyone has been inside the amp since assembly. I have read over many of the detailed BA series refurb threads here on AK, but many of them begin with an amp that is showing signs of a problem. I'd like to have some suggestions as to how I should approach looking over this lovely piece before applying any power. I have all the technical tools available for measurement and part testing (meters, scope, variac, generators, etc.) and have worked on a number of pieces in the past. My current train of thought:

Remove covers and clean and vacuum the interior and PCBs.
Inspect all PCBs and parts for signs of damage, overheating, etc.
Check all fuses.
Replace all VD1212 parts with 1N4148 dual diodes in series.
Check all transistor mounting (collector connection) bolts are tight, possibly removing and cleaning the PCB area first and then re-torquing.
Disconnect, clean, and re-seat all Molex connectors.

I'd appreciate thoughts from the large group of AKers with experience with these amplifiers and what other steps I should take.

Thanks!

 

[Overundr1]

Nice find
Download the service manual first of course
Pull the covers, blow out dust, do a visual look over. Would start it up on a dim bulb tester (100w bulb minimum) observing for any ill behavior and listening for relay click and front panel led change to green. If all good to this point go through and check offset and bias while on the dbt noting that bias will under read when not on full mains.

 

[grillebilly]

see above, manual at hifiengine. need to log on

https://www.hifiengine.com/manual_library/sansui/ba-5000.shtml

 

[LBPete]

Build a "Dim Bulb Tester" and use it to power it up. It will give you a visual indication of it's overall health. I'd do that before anything else so you have a base line. Start with a 60w bulb and if it's OK, go to 100w. This is the best way to power up a unit with unknown history.

I put some production information in your post in the Database thread.

- Pete

 

[Hyperion]

And if you do go on to do a full restore, each time you finish a board, or area of work, use the DBT at power up to check for anything amiss.

 

[audiolab1]

Thanks everyone!
I am unfortunately very busy this week with guests arriving shortly for the long weekend, so I have not had much time to dig into this beast yet. I did, however, have a chance to pull the top and bottom panels last night and have a look over everything and also downloaded the service manual. Thankfully it does not look like this example has ever been messed with and I cannot see any burnt or stressed parts or areas of any of the PCBs. Even though I could not see any evidence that anyone had been inside, and the layer of dust suggests it has not been for some time, I think that someone has re-greased the output devices. It looks way too fresh to be factory and there is a bit here and there on some of the TO-3 cases. I can also confirm that all of the output devices are the original Sankens. Next steps will be to give the inside a good cleaning and remove the driver boards for inspection and the check the collector bolts. I'm also digging around looking for my missing DBT...might have to put together another one!

 

[Overundr1]

Make sure the amplifier card next to the heatsink is fully inserted before applying power
Looks like either you had it out to look it over or may have dislodged during transport as the retaining clip is not locked over the end of the card.
-Lee

 

[Hyperion]

Good spot Lee.

 

[audiolab1]

Make sure the amplifier card next to the heatsink is fully inserted before applying power
Looks like either you had it out to look it over or may have dislodged during transport as the retaining clip is not locked over the end of the card.
-Lee

Good call! I have not removed the driver boards yet for inspection, so this must have happened in transit. Just one more reason I'm loving these forums. Thanks!

 

[audiolab1]

I finally had a chance to do a bit more looking over the BA-3000 today. The lovely summer weather has been keeping me outdoors, so I have not had much interest in audio lately. The driver boards and power supply regulator boards all look good with no signs of being stressed or overheated. The driver transistors have tooth washers both under the screw head and the nut. Was this normal procedure from the factory? I am seeing some thin, clear grease substance under the drivers. Not sure what it is but I will clean it off and apply white thermal grease when I get around to the refurb. I also discovered that I have the later amp block 2-sided boards with the early form of "vias". I am assuming that I only need to worry about the bus wire mods for the pads that connect front to back and not ones with wires or components in them? One question I have before bringing it up on a DBT is if it should be brought up slowly with a variac? Is it worth even powering this amp on with a DBT before addressing some of the weak parts of the design? Am I risking any damage? Finally, as I plan for a recap if the first power up test is ok with the DBT, I notice many people are using "audio" caps on the regulated power supply board F-2508. Most of those audio caps are only 85 degree rated...does it not make more sense to use high ripple current, 105 degree, long-life types on this board?

 

[audiolab1]

 

[Overundr1]

Absolutely bring it up on the dbt before doing any work, restoration or otherwise. This will allow you to pinpoint any faults in the amp before you begin changing parts. See, if you do not pinpoint faults first and start rebuilding and make a compounding error it becomes a real pita to sort everything out. Might use at least a 100w incadescent bulb to start with,then a 150w might be needed to kick the protection circuit off. Also note that if the amp has been off for a while the bulb will initially glow pretty bright for a couple of seconds before dimming down, more than 3 or 4 seconds shut things off before damage occurs. I have a variac on the bench however prefer the dbt for transistor use reserving the variac for tube work.
Nice pictures too.

 

[Hyperion]

There's going to be so much more 'air' and general ventilation around those boards when they get their new electrolytics, I can't wait to see the 'after' pictures.