Micro (Seiki) BL-91 restoration

[8991XJ]

They left enough wire such that I don’t have to unwind the wires from their posts.

We usually unsolder the wire wrapped pin instead of cut or unwind the wire. The wire wrap is an excellent connection. But I've done it both ways. I even had a recapped unit here where the guy doing that work cut all the wires leaving a stub of the insulation as a marker so the wires could be reinstalled properly. But that wasn't even necessary as I have recapped the same unit without moving any wraps, just positioning the board as needed for the work with wires attached.

I hate it when problems arise. Probably because I'm better at replacing parts than figuring out how stuff works which leads to determine why it doesn't work. Hope you get this one up and running easily.

 

[J!m]

Thanks, I hope so too.

It may be the switch itself, which would easily explain the behavior, but it’s obviously a nice switch and it “feels” fine. (Getting it out will be very difficult) Also, I saw a change in supply voltage (increase actually, which I figured was noise if some sort) when I switched it on the first time.

So, I’m currently stumped. My plan is to check the bridge first, then zeeners, to confirm their voltage, and if those are good start the deeper dive to check transistors. I am least comfortable with the latter and I don’t have every voltage listed on the schematic, but at least I have some of them.

Do zeeners fail open usually?

 

[laatsch55]

I've seen em both ways..

 

[J!m]

So, maybe that's good news....

 

[J!m]

Well, I once again confirmed the caps are all on with the correct polarity.

switch is tested good. It actually switches before the transformer…

Checked voltage at the zeeners and both are way low. Like 1/10 what they should be. Checked power for the LED and it is also way low.

Popped the board out so I can get probes on the back, and I have an EIGHT VOLT DROP across the bridge. I’d expect maybe one volt? I’m pulling that now. They should have it at the local place.

 

[NeverSatisfied]

If I am following along correctly, you did not verify operation prior to changing the caps?

 

[laatsch55]

A bridge should drop only a volt.or soJim, so you are correct on that. Check those transistors..

 

[J!m]

I was going to go one step at a time. Once the bridge is working I’ll confirm voltage at the zeeners. Maybe this got a lightning strike?

But I’m making progress at least.

And I rebuilt the spindle bearing. It’s a beast.



A tiny bit of wear in the thrust plate, so I flipped it. I may upgrade the ball to one of my polymer ones, but it’s 6mm and I don’t have that size on hand…

There’s a bronze sleeve bearing at the top and bottom of the shaft plus the thrust ball. I did my best to fill the void between the bushings with oil. Under the sticker is a vent plug which allows assembly- the fit of the shaft in the bushings is nearly air-tight.

 

[WOPL Sniffer]

Yeah, if you had caps in backwards, they send shrapnel flying pretty quick, especially in a power supply circuit.

 

[J!m]

They'd probably need to be fed power for that to happen... but none were in backwards.

I replace one at a time, checking value and polarity on each one as I go. Then double check before soldering anything.

 

[derek92994]

Speaking of problems, I was messing around with cheap chinese made 12 volt preamps, with plans to run them off the pure battery powered setup. Cut a Long story short, both boards pissed me off, combined with a rough week and several other events, one ended up like this:



Sticking to the mains powered PL 3600 from now on

 

[laatsch55]

A little noisy were they Darc??

 

[derek92994]

A little noisy were they Darc??

The first one lacked bass, even with the bass pot turned all the way up, then I accidently put the 2134 opamps in upside down which killed the board. No great loss, the opamps survived. The 2nd one sounded fine, but when I went to upgrade the caps on it, the board was near impossible to work with, really cheap nasty solder was used in the factory. Ended up destroying a few pads and that was it, lost my temper.

 

[laatsch55]

I love the fact you stopped and took a pic of your tempers result. I have a horrible temper too but keep a firm grip on it most of the time. There are some rocks and pumping units in the oilfield that are a recipient of some nasty ass temper ..

 

[J!m]

Brute force always prevails.

 

[derek92994]

I love the fact you stopped and took a pic of your tempers result. I have a horrible temper too but keep a firm grip on it most of the time. There are some rocks and pumping units in the oilfield that are a recipient of some nasty ass temper ..

It was worse when I was younger, the most important thing was to make sure the unit didn't piss myself or anyone else off, ever again! I took to that one with a 5 and a half pound weight. Was going to pour fuel on it and set it alight Luckily the boards were cheap, the Opamps were worth more. Got some spare NE5532's and Burr Brown 2134a's for a rainy day now. Would never destroy any of my precious audio gear intentionally.

 

[J!m]

Okay.

I’ve installed a new bridge and that’s not the problem. I had to get creative because no one has the same pin out in that thin package…



Now I have voltage going into it, but still the voltage is way low coming out.

If we look here, I should have 16V on one side of R36 and/or R10, and I don’t. No traces are broken so I look downstream to Q10 (2SD359). Data sheet I found is in Japanese…

Since C10 and C14 are both new and installed correctly, would this be your choice as well? I think it is being used as a voltage regulator but I don’t know for sure. There is nothing between the bridge and R36 for the LED but voltage is way low here and of course the LED does not illuminate.

I didn’t want to shotgun this thing but it’s looking that way now…

 

[J!m]

Fixed it. Another broken trace (like the 880) that’s probably my fault…

Anyway, it’s working now. Totally silent motor… I saw the led and touched the motor pulley to tell it was turning. Both speeds too!

 

[J!m]

And on a more positive note: the weight showed up today!

 

[NeverSatisfied]

Persistence pays, well done. Going to be a really nice table Jim.