SONY PS-8750 on eBay

[Yamaha B-2]

Not sure if the base is covered in some ultra-thin layer of vinyl or melamine or if painted. The tags on this machine, one on the back of the base and the other in post #49, both feel off. Believe this was due to the moisture I alluded to in my previous post. When finished, I'll put them both back on once everything is running well.

One problem with this TT is the lack of access to the insides without turning it on its back. Then, of course, one can't reach the controls, the platter must be removed and the TA is not really in the optimum position to run correctly and be set. The neon bulb and CdS sensor for the automatic features of the TA movement have adjustments, as does most everything on this TT, so will start playing with them shortly. Have removed the base and letting it 'dry', in the event any moisture is left in there. Next step is some Deoxit.

Serial Number is 800579.

 

[Yamaha B-2]

Had some more time to play with the PS-8750. Results are:
- Doesn't lock in when the Xtal Lock position is selected. Runs slow and hunts. Locks-in perfectly in the standard position.
- Auto-function motor does not operate. Hopefully, this is something electronic and not the motor.
- Sound is fine once the ground is properly connected.

Giving serious thought to removing the electronics from the base of the unit and building a separate PS/controls enclosure. Will be simple enough to do and use of a couple of Amphenol connectors should make the interface at either end bullet-proof. Think I will also remove the arm to preclude any chance I'll f-it up in my work. Will be a fairly long-term process as I have a few other items on the 'must do' agenda, first.

 

[axel]

... just found this full-size nudie of a japanese PS-8750...

 

[junkaudio]

very nice tt .gotta buy one

 

[Yamaha B-2]

Axel - check post #56 in this thread. Thought that looked awfully familiar (and not just because I have one ).

 

[axel]

oh, well - now we know japanese models have the fuse to the left and european models to the right

 

[EchoWars]

Had some more time to play with the PS-8750. Results are:
- Doesn't lock in when the Xtal Lock position is selected. Runs slow and hunts. Locks-in perfectly in the standard position.
- Auto-function motor does not operate. Hopefully, this is something electronic and not the motor.
- Sound is fine once the ground is properly connected.

Giving serious thought to removing the electronics from the base of the unit and building a separate PS/controls enclosure. Will be simple enough to do and use of a couple of Amphenol connectors should make the interface at either end bullet-proof. Think I will also remove the arm to preclude any chance I'll f-it up in my work. Will be a fairly long-term process as I have a few other items on the 'must do' agenda, first.

For some bloody reason, this unit has gotten dumped on me to sort out. :scratch2:

Unda Maris's observation of dried caps is spot-on. The 10µf 350V cap for the strobe light was toast, and allowing tons of AC to invade the logic (and the lamp would go 'bright-dim-bright-dim )...I had a 22µf 450V cap laying around and that fixed that. But, not only that, the 5V supply was also the victim of bad caps, so the servo amp board was recapped as well.

At first, once the recapping was done, the quartz locked speed was dead-on at 33.3, but miles off at 45. Started fooling around, and then lost both the 33.3 and 45 lock. Fooled around some more and the 33.3 came back. WTF?

Freeze spray baby! :thmbsp: Shot a few IC's, and both the 33.3 and 45 came back until the IC's warmed back up. I suspect that the excessive ripple from the dried-up caps has damaged the digital IC's, so not only am I going to replace the ones that I found are intermittent, I'm going to replace all of them.

Designation     Old Number    New Number    Description      
IC102~106        M53200P       74HCT00       Quad 2-Input NAND Gate
IC107            M53210P       74HCT10       Triple 3-Input NAND Gate
IC108            M53220P       74HCT20       Dual Quad-Input NAND Gate

No more Japanese logic IC's, this is getting new Texas Instruments devices, and gold sockets. :yes:

IC101 is a strange one, a MSM5576 oscillator/divider chip. I'd replace it too if I knew what would work, but hopefully it will remain working as intended.

Dunno what's up with the auto functions. Hopefully it's just the belt, but until the IC's are replaced and the speed is working it's a waste of time to fool with it.

 

[Yamaha B-2]

EW - All right!! :thmbsp: While you are waiting for ICs can you go ahead and recap the rest of the system? Since none of this is in any audio circuit, BGs are not necessary (as if you don't know that). I'll give you a call Thursday to confirm my arrival on Saturday. 2pm is looking good.

 

[Unda Maris]

EW, B-2

as you might know my PS-8750 has the same problems.

I also changed several Logic ICs, but the problem did come back.

I still think it has something to do with the manually soldered trough hole vias.
Some of them had a significant resitance over them, so I resoldered a few.
The problems went away and came back ...

My ST-A7 tuner has also this strange type of double sided boards and it has comparable problems ...

This is a really strange circuitry. The frequency dividers are far away from any textbook solution, looks more like a magic "voodoo" solution, which works from time to time or if the gods have mercy.

Btw. if you use HC/HCT types it might not work or the chips might get damaged. If possible you should use original (Texas) TTL chips.

 

[EchoWars]

Btw. if you use HC/HCT types it might not work or the chips might get damaged. If possible you should use original (Texas) TTL chips.

Wonder why you'd think that...the HC and HCL chips use the same supplies as the original (+5V) and recognize the same logic levels. The differences are in the internal construction of the device, of which we don't really care as long as the job gets done.

 

[Unda Maris]

I don´t know if my comment is really correct, but these trick circuits use
something like capacitor coupled digital signals, which might exceed the supply rails (+5V and GND).

Doing this, CMOS types react different than TTL or LS TTL gates.

But because I don´t have the schematics ready, I might be wrong ...

 

[EchoWars]

Cap-coupled or not, with a 5V supply that's your ceiling. Q101 and Q102 are interfaced to the logic IC's to provide a correction signal and reset signal (respectively), and use the same 5V supply as the logic does.

I plan on completely removing the logic board for the refurbishing, and checking out all the feed-through's you mentioned. Reflowing the solder on them should eliminate any issues. And since the new logic IC's will be socketed, they'll be a breeze to replace if there's any trouble (which I doubt).

 

[Unda Maris]

This sounds like a very clean solution !

 

[EchoWars]

Well, it turns out that the 74HCT00-series is not suitable. They work for about 10 seconds, and then go into uncontrollable oscillation. I don't know if it's a layout issue, or improper bypassing, or what, but basically they are too unstable.

What is needed is original 7400-series devices. I found a few places on the web, as well as Consolidated Electronics that apparently has some of the original Mitsubishi chips.

For now, I cleaned up the leads of the original chips and stuck them in the sockets. Same thing...no speed control.

BUT...the speed would lock in every time I freeze-sprayed a section of the PC board. So with soldering iron in hand, I re-flowed the solder on all the pass-through's in that quadrant of the board (about 10 or 12 of them). Speed locks fine now, but I'm wary of the original logic IC's still.

The best devices for the job would be TI-series 7400 chips - SN7400, SN7410, and SN7420. Not easy to find...

Oh...and the auto-return is fixed. :yes:

 

[Yamaha B-2]

To say that I am psych'd is a gross understatement! :thmbsp: See you tomorrow.

 

[EchoWars]

Well, the speed has decided to flip out again. Worked for 3 or 4 hours last night, and today it has decided that it don't wanna go.

Hopefully the full chip replacement will take care of it. In the meantime, I'll try to resolder a few more passthroughs.

 

[Yamaha B-2]

Well, obviously, at least to me, whatever else you did was your typical magic and all is working well for the second day in a row. I've ordered the easy-to-find ICs (~$10 for the set) and put out a search on the unobtanium oscillator IC (wish me luck).

Next step is to decide exactly what I want to do for the base. Think I'll make a 2" high spacer to replace the existing base and then have a piece of granite cut and polished that is about 2" wider and deeper than the existing plinth. Will sandwich the wood (cherry?) between the two, drill the corners of the granite for spikes and then be ready to go. Let's see. This looks like indoor project number 5, so should get to this by next spring, if I'm lucky.

 

[EchoWars]

Cool.

Spent a lot of time on that...I'd like to think is was not for naught.

 

[Yamaha B-2]

OK. Time to post a pic of the finished product. Here she is all dolled up with the Ortofon Kontrapunkt b. Compared to the Yamaha PF-1000 I would say the sound has more "presence". That is, is just more "live" sounding. Of course, this is after one LP. Even if it is Miles "Kind of Blue" in a 200g pressing. Red wire is the temporary ground that took care of the minor hum I was getting. Using Cardas wires between the K-b and the headshell and a set of Wasatch 105U ICs. Plan to try a set of silver ICs at some point.

 

[Vinyl Rules!]

OK. Time to post a pic of the finished product. Here she is all dolled up with the Ortofon Kontrapunkt b. Compared to the Yamaha PF-1000 I would say the sound has more "presence". That is, is just more "live" sounding. Of course, this is after one LP. Even if it is Miles "Kind of Blue" in a 200g pressing. Red wire is the temporary ground that took care of the minor hum I was getting. Using Cardas wires between the K-b and the headshell and a set of Wasatch 105U ICs. Plan to try a set of silver ICs at some point.

So how does the Sony PS-8750 compare to your mint Sony PS-X7 TT?