sansui 890 problems

Choices becoming more limited however---

2SA818 replace with 512-KSA1220AYS
2SC1628 replace with 512-KSC2690AYS

both are in stock at Mouser

Sansui used those transistors frequently and they had a 1watt rating. The listed subs are more than capable current wise and close enough in hfe to preclude oscillation issues imho. There are a couple of other transistors that we used that now are obsolete and to recommend them might just land you squarely in the fake transistor market.

sansui 890

When ordering resistors please recommend specs. ie (film)? temp? tolerance? Voltage? Lots to choose from. Thanks

the 8080 schematic IS accurate for the 890… the only thing that changed id the front panel…..

sansui 890

I am unable to load pics, need moderator help. Invalid post specified.

"When ordering resistors please recommend specs. ie (film)? temp? tolerance? Voltage"

I use film, others like metal oxide, still others throw in whatever 1/2 watt matching carbons they have on hand, not critical here other than getting them changed
1/2 watt for all, and I forget the reason why the 1/4 watts are not used where mentioned on the schematic other than there are locations where 1/4 watt is barely sufficeint
temp not important
tolerance 1% if available
voltage not critical either

At issue here is the fact that those old fusibles almost certainly have drifted high and need to come out, beyond that they are 'just' resistors and only need to keep their tolerance for downstream voltages. Remember V=I/R and a rising R will give reduced V.
-Lee

sansui 890

Thanks Lee should be placing an order tomorrow. I had the replacement transistors you mentioned. The originals were installed in a straight line. The replacement transistors ksc2690ays and ksa1220ays are ECB, therefore the collector and base legs had to be crossed in order to work. Thanks

I am no expert in posting pics, but when you try to add images did you upload from a file on your computer to AK?

sansui 890

Yes I did try uploading from computer just as I typically do. When I hit the upload I get the response in post 24. thanks

E mail the pix to me & I'll post em
vigman@earthlink.net

sansui 890

I need to get this resolved and appreciate your help. F 2436 Driver board C7 and c8 do not have a pos or neg schematic symbol. Does it matter which way the caps are installed ?

C7 and C8 are non-polar and can insert either way.

sansui 890

Thanks Lee, when setting bias 50mv, please advise on process. Per user manual I want to be clear. There are no readings on the driver board for F08 and F07. May I assume they are the most interior fuses? Also how to get a multimeter probe where the neg should be? There is no room. Also should the fuse be out when taking measurements? Thanks as always

First off 50ma is too high and just makes your receiver act like a toaster. My recommendation is to set bias to 30ma each channel. Anyways---

Be sure your multimeter is set to ma not mv and note whether you have to change the meter leads to a different set of sockets (some do) for ma measurements.

power off
remove F08 fuse
using mini grabbers connect meter across fuse terminals

power on
adjust vr04 (right channel closest to left edge of board) to 30ma
power off replace fuse

repeat for left channel F07 and vr03 (left channel closest to right edge of board)

Once they are close run the receiver for about twenty minutes and monitor the bias to ensure it does not drift high as the unit warms up. There really is no pattern to this, could rise or fall depending on topography. Remember, when in doubt start below spec and sneak up on desired value. I also have a towel draped over the heatsink to aid in warm up time.

Note: when I set bias I use two meters at once to observe readings and make it a one shot deal. Hopefully you already replaced both trimmers to prevent magic smoke if one of the old trimmers fails.

I also encourage having a supply of multimeter fuses on hand just in case
One of these days I need to work out emitter resistor measuring points and mv values instead of the fuse and ma routine.

I am assuming that you have adjusted bias before and understand that overly enthusiastic bias tweaking can be hazardous to your output transistors. If more detail needed let me know.
-Lee

sansui 890

Thanks Lee