Yet Another Sansui 9090DB Rebuild Thread

I'm re-capping a Mac 4100 for a coworker and in exchange he's trading me a 9090db that won't come out of protection. I've got a little thread going on over in the mac sub-forum about that rebuild. I've got the parts lists compiled and I'm waiting to hear back from Mac about suitable replacements for the tape push buttons before I place an order...

Now I'm digging into the Sui that was already given to me. As stated the unit is stuck in protection. First things first I checked all fuses and gave a good round of de-oxit to all switches/buttons/pots. All fuses were good, all switches are clean, and we're still in protection.

So off to these lovely forums I went and found a treasure trove of information on this topic. This place is seriously awesome. My 90 minutes or so of AK education taught me F2624 would be a good place to start. To that end I pulled that sucker out and found some good news: there are readily apparent issues! Somebody else has been in here previously and buggered it all up! TR01 and TR03 have been replaced transistors that are not a KSC1845 as is recommended by @Trnsfmr in that awesome thread of his. This seems to have caused R11 and R21 to burn themselves up.

Also of note are several other replacements done by Mr. Fixit.

C05, 06
R44
VR03, 04
TR09, 10, 14

Those have all been replaced. Mr. Fixit made an interesting decision when he replaced VR03 and VR04 by mounting VR04 on the component side and VR03 on the foil side. That doesn't make any sense to me.

Considering all that I think it's safe to conclude that this board is the culprit. All parts that have previously been messed with I am going to replace with the correct parts from the best information I can find here. I am also going to replace the other 6 original electrolytic caps and R33 and R34 (even though they test right around 180ohms) while I'm at it.

The service manual states VR01 and VR02 are 4.7k and VR03 and VR04 are 1k VR's. I haven't ever sourced variable resistors before. Can someone tell me what I need to do with that information so I can get the correct part?

I also hope Littlediode still has the 2sc984's available to use in the TR09, and TR10 spots.

After I get this sucker out of protection I plan on completing a full rebuild on it.

Other areas the unit needs attention in if I complete the rebuild and the unit is fully functional are:

- replace the power switch which is broken off outside the face-plate
- find two silver caps for the filter buttons and a knob for the mic volume
- LED bulbs
- build a nice new hardwood case.

I'm really excited for this project. I think it is going to be fun and I managed to get my hands on a "monster" receiver without having to pay an arm and a leg. My coworker feels like he's getting a good deal too because he bought this cheap with the intention of it being a first rebuild project, but now thinks he'll never get to it. So when I suggested this trade he was all about it.

 

I found out in the F2624 thead currently on the front page that you can take out that board, turn the unit on, and see if there are protection problems elsewhere. I did that and it would seem I'm out of luck because it's still in protection. I also took out the fuses on the protection board with the same result.

I want to be able to isolate this problem before just randomly replacing parts. So first it would be best to get it to come out of protection with the driver board out, then hopefully go into protection if I put the driver board back in.

This particular unit does not have the plastic sleeve coated fuses on the power supply. I suppose I ought to replace the two fusible resistors in the power relay and check the outputs as well. Anything else I should be looking for?

 

Check the output transistors and their emitter resistors.

Rob

 

Use 25 turn Bourn trimmers to replace the original trimmers. They are available in 1k and 5k values. That said there was a major revision to the driver board midway through production. The values posted are for the early generation board with transistor bias control. The service manuals were printed well before this production change. In your first picture it looks like you have the later production diode bias control version. That generation of the board uses a 100 ohm trimmer for bias adjustment and 4.7k for DC Offset.

If your board has black diodes mounted at the top of the heatsink, you need 100 ohm and 5k bourn trimmers.

If your unit stays in protection with the driver board removed, do as Rob said, check the outputs and emitter resistors.

In your research on this board you must have come across threads discussing the fusible resistors. they need to be replaced with metal film equivalents. They are the #1 reason for these receivers being in protection.

- Pete

 

I checked all the emitter resistors in circuit and a couple read as low as .2 ohms. Should those be replaced? Should I go ahead and replace all 8?

I pulled all the output transistors. Mr. Fixit has been back here working his magic as well. TR04 and TR07 have been replaced with 2SB600's. It looks like all others are original. TR02, 04, 05, and 07 test fine. The other four are all bad. I've been trying to find out which side of F2624 is R/L and which set of 4 Outputs is R/L. I'm hoping that (from the first pic in my OP) the left side of the board corresponds to output TR01, 03, 06, and 08, which are the 4 bad ones.

@LBPete, thanks for the VR explanation. I'm unsure which diodes you're talking about. If they're not D15 and D16 pictured in the first pic above the four transistors with individual heatsinks I'm not sure what other heat sink to look at.

Lastly, I cannot tell if the Power Relay board just looks new having been shielded from dust (since it's mounted upside down underneath parts of the chassis) or if Mr. Fixit has already had a go at it. Is the Omron MY3-02-DC24 the exact same relay that was used back in the 70's? If the answer is no then Mr. Fixit has beat me to it! I looked in the service manual for a part number for the relay and all it says is "relay", which is very helpful.

 

The thermal compensation diodes to which Pete refers are a modification Sansui introduced which replaced TR09/TR10 and they are mounted on the heatsinks of TR13 and TR14.
D15/D16 are part of the current limit network.

 

Ok, mine is the diode version. One is redish/brown and the other is green and I'm pretty sure they're both new. I had read something about using multiple diodes in parallel as a replacement for something. This must be it.

 

Those diodes are not original and the colors you mention make them suspect. There are other versions of that type of diode and you need the correct version. The originals are STV3H diodes and are black. If those are indeed the wrong diodes, you will never get bias current set correctly.

The newest picture of your driver board plainly shows the dreaded fuseable resistors have not been changed. The ones at the outer edge near the connector should be 180 ohm and frequently go open. That will put it in protection for sure.

It's best to take the emitter resistors out of circuit to test. Just unsolder one leg. Have you checked the output transistors out of circuit? Odds are several are blown. It shouldn't be hard to trace the circuit on the power supply board connector and the outputs to determine which is left and right on the driver board. There are good modern replacements available.

The relay part number you mentioned is the correct replacement relay. The original relay would have had "AU" and I believe "US" in the part number on the top of the relay.

- Pete

 

Pulled a leg on the emitter resistors and they all appear to be fine. Sometimes my DMM was having a hard time settling down with them, though. Not sure if that's bad or just because of some overly dusty legs in there.

I pulled the Output TR's when I tested them. I traced the board and the four that are bad are in the same circuit as the side of the driver board that's been messed with. That's encouraging.

These are the Trimmers I found searching for Bourns 25 turn. Are these are correct?

https://www.mouser.com/ProductDetail/652-3296W-1-472LF
https://www.mouser.com/ProductDetail/652-3296W-1-101LF

Are there any transistors in this unit that need to be matched when installed?

I'm putting together a rather extensive parts list for when I get started. I think I might add the emitter resistors just for grins. Will any 5W .33Kohm resistor work? They aren't included in any parts lists I've found.

Once I get the parts my general plan is to replace all the fusible resistors in the unit that are not on F2624 and replace the 4 blown outputs and see if it'll come out of protection with F2624 out. Is there anything else I should check or test before I place an order?

 

If the emitter resistors check good, there is no need to replace them. Those are correct trimmer series but you need the version that mounts at a right able to the board. If you use the ones in the link they will be a bitch to adjust. https://www.mouser.com/ProductDetai...=sGAEpiMZZMvygUB3GLcD7sSg8po3Zpo3Rj6axJ/leGw=

Be careful about replacing parts wholesale. Before replacing the output transistors check the driver transistors on the driver board. They are the ones mounted vertically on the heat sinks. If they are OK, then install the new output transistors. Replacing the blown outputs should allow it to come out of protection with the driver board out. You also need to replace the fusible resistors on the driver board. They are the #1 cause of protection issues with this model.

- Pete

 

Thanks for the correction on the trimmers.

My goal is to get it to come out of protection without putting the driver board back in. I know the driver board has issues, so I'm going to tackle those after I figure out what is causing the protection elsewhere. I guess I'm confused why I need to check the driver board driver transistors before I complete all that. Don't read that like I'm pushing back, I'm just genuinely unsure of the reason.

Replacing all the fusible resistors is on the list for the driver board when the board sees its time on the bench. If I can get the unit to come out of protection with the driver board out I wasn't going to put it back in until I do a complete overhaul per @Trnsfmr with (I'm sure) plenty of advice sought in this thread along the way.

 

Yup, one step at a time. You don't need to check the driver transistors before replacing the outputs and checking to see if that allows it to come out of protection. You do need to check the driver transistors before re-installing the driver board. Carry on.

- Pete

 

Perfect, thanks for your help and sharing your expertise. The parts for the Mac 4100 project came in today and I'm gonna finish that up before I dig any deeper into the Sui. But I'll be back in a few weeks.

 

Welcome to the Sansui side of the AK fence. Lots of experience here on the xoxo series. Anyways, I might humbly suggest you carefully remove those supposed stv3's noting lead orientation and measure the voltage drop across the leads, if memory serves me they should be somewhere in the 1.8vdc range. Also as stated above any fusible resistors need to be filed carefully in the nearest round filing device you have handy. Finally very bad things will happen if you happen to put that driver card back in one pin off, also those trimmers adjust differently depending on the channel you are working with.
-Lee

 

Aaaand I'm back! 4100 has been rebuilt successfully and after a couple weekends of too much stuff going on I'm tearing into this sucker.

First thing I decided to do was take all the emitter resistors completely out and test them again. On the whole they don't want to test very well. They'll read .3-.4 ohms for a second and them jump all over the place. I'm not sure if the leads are too old and corroded and it's a connection issue or what, but I'm just going to order new ones to make myself feel better. It's 6 bucks for ten 603-SQP500JB-R33 on mouser.

Right now I'm going to pull all the caps and fusible resistors off the power supply and replace those as well as replace the 4 blown outputs. Once the emitters arrive I'll throw them in, power up on a DBT without F2624, and see what happens.

 

It's been awhile, how about a re-fresh on what's going on with your receiver to get us re-focused. What exactly are we trying to fix?

- Pete

 

Here's the (pun intended) recap!

End goal: Full restoration/rebuild

Condition: beat up and won't come out of protection. Someone else has tinkered on F2624 and the protection board and probably caused more damage than they solved. All 4 right channel outputs are blown and there are melted resistors on the corresponding side of F2624. Won't come out of protection with F2624 out presumably because of the blown outputs.

Known burned/out of spec components:

- R11 (blown), R21(blown), R33, R34, R41, R42, R47 on F2624
- Output transistors TR01, 03, 06, 08

Known replaced parts by the person before me:

- R44, VR03, VR04, C05, C06, TR01, TR03, TR09, TR10, TR14 of F2624
- Output TR03, and TR08
- The relay and possibly a couple components on the protection board, but I haven't dug far enough to know for sure yet.

What I've done so far:

- pulled all outputs and found the 4 bad ones
- pulled all 8 emitter resistors completely off the power supply and decided to just get new ones. They tested somewhat erratic as explained in my previous post.
- Replaced all electrolytic caps and the three fusible resistors on the power supply. Once the new emitter resistors come in I'll put them in and see if it comes out of protection (with F2624 out and new outputs in of course)
- While I'm waiting for the ER to arrive I started pulling components off F2624. I have everything on hand to replace all the electrolytic caps, fusible resistors, and all the transistors recommended in the "Restoring the f2624" thread. I started on F2624 because there's no way it's going back in the unit in its current condition. Once we get the protection issue figured out I'll have f2624 ready.

That's where I'm at. Other things the unit will need before this is over is a new power switch and a couple buttons.

 

The only parts I do not have for F2624 are the STV-3H diodes. Looking on the auction site it seems there is a supplier out of Germany with quite a stock and there's also someone selling an SV-03Y axial diode they say is an STV-3H equivalent. Currently (see pictures) there's a red 53A and a green 56A on the board. I'm going to assume these need replaced with the correct part. What would be the most reliable way to get a hold of a couple of the correct diodes? I'd read mixed results about littlediode.

 

You should be able to check the STV-3 diodes with the diode check function of you DVOM. See post #14 in this thread. Let us know how the new outputs work out.

- Pete

 

if the seller in Germany that you're looking at is sh-halbleiter you're in the right place. Used him several times...