SX 1250 FROM SCRATCH

[rhodus]

In many cases you are improving on the original by using new parts. The connectors and switches are silver plated which we all know is a Achilles heel but if you polish them up they are good for years. It is kind of nit picking because even the speaker terminals are kind of a joke for a serious power amplifier but where do you start and where do you end in this journey or $ sink hole

Yea, I'm really not a fan of the connector plugs either. I think good quality screw terminal strips would be far better. I've read varying viewpoints on the speaker terminals, both pro and con. As an Electrician, it does seem that fine stranded 14 gauge copper wire can carry far more current than the 1250 can supply but the spring loaded thing does leave a little to be desired.

 

[tarior]

Those connector pins clean up very nicely with some Brasso or Flitz, then treat them with G100. I, for one, am glad that the boards can be unplugged and completely removed for ease of service.

 

[rhodus]

Those connector pins clean up very nicely with some Brasso or Flitz, then treat them with G100. I, for one, am glad that the boards can be unplugged and completely removed for ease of service.

Do you know a safe way to clean the female connectors besides just flushing with deoxit or such?

 

[tarior]

Oddly enough, the female side hardly ever seems to crud up. Look at one with a magnifying glass.

 

[rcs16]

The 1250 has a nice layout. It is however difficult to probe the pcb's mounted vertically in that tight space, esp. with power applied. Kind of forces you to trouble shoot with them removed, using the ohmmeter, which is the way it should be done anyways in many cases if you are looking for out of spec parts.
If you have a test jig then it is easy to test with a proper supply. This is how I test the new PS's or any other design.

The contacts could be tin plated brass as many are. gold contacts shine
i just spray the contacts with some deoxit and polish the pins

the 1250 PS is better positioned compared to models having it on the bottom like the 1980.
They should have just flipped them upside down and problem solved. The PS would cool properly and less dirt getting into the tuner gangs.

There is a new PS pcb for the 1250 in the works, more HS in order to run the parts cooler, new parts, design improvements. I need to verify it for fit since I have added terminal blocks in replacement of those connectors which we agree can be improved upon in that regard.
Lucky someone local wants their beloved 1250 refreshed, so I have one to use a mech sample.

Happy restoring
Rick

 

[tarior]

With the 1250, it's not too tough to add a little extra heat-sinking to keep the heat from going into the board, thanks to its vertical orientation.

 

[zebulon1]

The vertical boards can be checked in circuit.
With the receiver on its side vertical.
Pull the molex plugs out so they are facing the bottom and plug in the board having it hang with an insulator on the bottom of the chassis. It works. I wish I could find a picture of the procedure.

 

[rcs16]

That's right, someone with a lot of experience speaks. The pwr amps I do not think so.

Yeah we were contemplating on putting in a new PS or leave it stock. Owner/we decided to leave it stock, had the box of ecaps and parts for the PS already, so it will probably be just that, PS heatsink upgrade too
So one wonders if you are adding all this extra HS, it is not stock anymore so ...?
I think that big PS HS is made of steel, I'll check, it would be better if it was aluminum but a self adhesive 25x25mm pin array HS should work out okay. I think . Those smaller ones could get some extra. The more I think about it, it would be faster to just build a new one

 

[rhodus]

The 1250 has a nice layout. It is however difficult to probe the pcb's mounted vertically in that tight space, esp. with power applied. Kind of forces you to trouble shoot with them removed, using the ohmmeter, which is the way it should be done anyways in many cases if you are looking for out of spec parts.
If you have a test jig then it is easy to test with a proper supply. This is how I test the new PS's or any other design.

The contacts could be tin plated brass as many are. gold contacts shine
i just spray the contacts with some deoxit and polish the pins

the 1250 PS is better positioned compared to models having it on the bottom like the 1980.
They should have just flipped them upside down and problem solved. The PS would cool properly and less dirt getting into the tuner gangs.

There is a new PS pcb for the 1250 in the works, more HS in order to run the parts cooler, new parts, design improvements. I need to verify it for fit since I have added terminal blocks in replacement of those connectors which we agree can be improved upon in that regard.
Lucky someone local wants their beloved 1250 refreshed, so I have one to use a mech sample.

Happy restoring
Rick

Keep us posted on that new PS.

 

[tarior]

With the schematic and wiring diagram, you can check P/S voltages all over the place in the 1250. Pioneer service documentation back then was unparalleled.

 

[merlynski]

Do you know a safe way to clean the female connectors besides just flushing with deoxit or such?

On my SX-1050 I used silver polish on pipe cleaners (the scratchy ones), then with water wetted ones to clean out the residual polish, Silver polish on cotton swabs for the pins. No abrasive needed to polish the pins.

 

[merlynski]

The vertical boards can be checked in circuit.
With the receiver on its side vertical.
Pull the molex plugs out so they are facing the bottom and plug in the board having it hang with an insulator on the bottom of the chassis. It works. I wish I could find a picture of the procedure.

Picture of my SX-1050 on its side, with the power amp pulled outwards and the heatsink plugged in and supported for live action trouble-shooting:




The Receiver is sitting on a 15" lazy susan / turntable for easy rotation.

 

[tarior]

That's quite the setup.

 

[Watthour]

Oddly enough, the female side hardly ever seems to crud up. Look at one with a magnifying glass.

Forget the magnifying glass. I've been studying the female side under a microscope for decades, and I still haven't figured them out.

 

[rhodus]

Yesterday I powered up the amp section just out of curiosity. Dim bulb first, of course. Soft start seems good, bulb dimmed....Yahoo! I got the power supply set to 65v and moved on to the amps...DC offset off the chart, all 4 boards I have to experiment with tested 150-295mv, protect relay not engaged...I'm going to rebuild the plug in boards before I go any further....

 

[rhodus]

Looking for suggestions for C13 on the the stabilizer board. Mouser shows 647-TVX1V102MCD to be obsolete. They do have this....871-B40600B7108M001. Its a TDK/Epcos Aluminum Organic Polymer $5.06 ea

 

[Watthour]

It doesn't have to be an audio-grade capacitor. Anything with a good ripple factor and a minimum 35 WVDC rating will do well there. Since the area can experience general heating it would be good to get something rated for 105°C or higher.

 

[markthefixer]

it also does not have to be an axial cap - several axial caps on the sx-1980 have been "converted" to radial.

A bit more of a pita to mount, but no big deal.

 

[rhodus]

It doesn't have to be an audio-grade capacitor. Anything with a good ripple factor and a minimum 35 WVDC rating will do well there. Since the area can experience general heating it would be good to get something rated for 105°C or higher.

I just checked and the only other 105 degree option is a Vishay that actually costs more...$5.39 ea. The TDK has a 150 degree operating temp...I'm gonna check DigiKey..

 

[rhodus]

it also does not have to be an axial cap - several axial caps on the sx-1980 have been "converted" to radial.

A bit more of a pita to mount, but no big deal.

How about this....80-EST108M035AL4AA