New here, 700II and 4000

[SG700II]

Hi guys, recently was gifted a PL700II and a PL4000 P.Amp, in original boxes, perfect condition.

By a coworker who bought them new in the 1970s, and had them in his garage since the 90s.

I already swapped out all the factory fuses for the corresponding agx, and the capacitors for Nichicon UFG, and ordered the WO Aishi main filter caps yesterday. Sounds great as it is.

 

[mlucitt]

You are a lucky guy!

 

[George S.]

Classics!

 

[J!m]

Those look great!

Welcome to the jungle.

 

[SG700II]

Thank you guys, stoked.

 

[MarkWComer]

It’s rare to see them in that condition. Congratulations!

 

[MarkWComer]

Left sensitivity control set at minimum, but LED panel shows output…
What’s going on there?

 

[SG700II]

Left sensitivity control set at minimum, but LED panel shows output…
What’s going on there?

That was prior to the caps being replaced. No longer doing it.

 

[SG700II]

 

[wattsabundant]

I hate to be a buzz kill, but the 4000 is a (small) time bomb waiting to happen. If you pull the bottom cover you'll likely see hundreds of cracked solder joints on the mother board. Reflow the solder around the pins. The phono jacks also like to breaK. I bought a few hundred last year on a close out deal.

The 700II (and the 400II) has a resistor on the main driver board, R101 (7.5K/2W) that likes to fail. If it does it sends100 volts DC into the speaker likley resulting in damage. There is a relay board available that protects the speakers from such disasters. I'll let other people comment on the merit of that.

If low frequency response is poor, there is a capacitor on the 700 driver board that frequently fails. Lastly, a lot of hum and buzz can be attributed to the main 9800uf capacitors that are likely failures. White Oak Audio has a solution for that. If the displays seem to act up there is a capacitor on them that fails.

Is there a recurring (capacitor) theme her?

Service manuals attatched.

 

[SG700II]

Thank you for the information, taking notes and learning as I go. Currently eyeing the relay board. I also have a SX950, which got me used to having a relay at startup. Plus the speaker protection feature is a must.

 

[laatsch55]

Yep...

 

[marcok]

I restored 2 PL 4000 units , so I would add some other considerations :
- mother board and front board are critical below S/N 2000
- caps values are critical (35 V in stead 63 V ) below S/N 5000
- RCA connectors are really a disaster ( they are too fragile after 45 / 50 years )
-Output relay is no good for PL 700
Conclusions ( suggestions ) :
-Replace RCA connectors
-Check and eventually replace caps
-Short the 2 legs of output relay to increase the max . current
Follow the last version of service manual (rev. 6 81 )
available on HiFi engine .
Ciao
Marco

 

[SG700II]

I restored 2 PL 4000 units , so I would add some other considerations :
- mother board and front board are critical below S/N 2000
- caps values are critical (35 V in stead 63 V ) below S/N 5000
- RCA connectors are really a disaster ( they are too fragile after 45 / 50 years )
-Output relay is no good for PL 700
Conclusions ( suggestions ) :
-Replace RCA connectors
-Check and eventually replace caps
-Short the 2 legs of output relay to increase the max . current
Follow the last version of service manual (rev. 6 81 )
available on HiFi engine .
Ciao
Marco

Thank you for all the knowledge. Really grateful.

 

[SG700II]

I restored 2 PL 4000 units , so I would add some other considerations :
- mother board and front board are critical below S/N 2000
- caps values are critical (35 V in stead 63 V ) below S/N 5000
- RCA connectors are really a disaster ( they are too fragile after 45 / 50 years )
-Output relay is no good for PL 700
Conclusions ( suggestions ) :
-Replace RCA connectors
-Check and eventually replace caps
-Short the 2 legs of output relay to increase the max . current
Follow the last version of service manual (rev. 6 81 )
available on HiFi engine .
Ciao
Marco

Any particular type of caps you recommend ?

 

[SG700II]

I hate to be a buzz kill, but the 4000 is a (small) time bomb waiting to happen. If you pull the bottom cover you'll likely see hundreds of cracked solder joints on the mother board. Reflow the solder around the pins. The phono jacks also like to breaK. I bought a few hundred last year on a close out deal.

The 700II (and the 400II) has a resistor on the main driver board, R101 (7.5K/2W) that likes to fail. If it does it sends100 volts DC into the speaker likley resulting in damage. There is a relay board available that protects the speakers from such disasters. I'll let other people comment on the merit of that.

If low frequency response is poor, there is a capacitor on the 700 driver board that frequently fails. Lastly, a lot of hum and buzz can be attributed to the main 9800uf capacitors that are likely failures. White Oak Audio has a solution for that. If the displays seem to act up there is a capacitor on them that fails.

Is there a recurring (capacitor) theme her?

Service manuals attatched.

Do you recommend a particular kind of resistor ?, was looking around and the ceramic type, at that value seems hard to find.

 

[wattsabundant]

I restored 2 PL 4000 units , so I would add some other considerations :
- mother board and front board are critical below S/N 2000
- caps values are critical (35 V in stead 63 V ) below S/N 5000
- RCA connectors are really a disaster ( they are too fragile after 45 / 50 years )
-Output relay is no good for PL 700
Conclusions ( suggestions ) :
-Replace RCA connectors
-Check and eventually replace caps
-Short the 2 legs of output relay to increase the max . current
Follow the last version of service manual (rev. 6 81 )
available on HiFi engine .
Ciao
Marco

I take exception to the comments on the relay board. I use 20 amp relays. Thus far no report of relay failures in 400 or 700.

 

[SG700II]

I take exception to the comments on the relay board. I use 20 amp relays. Thus far no report of relay failures in 400 or 700.

Im looking right now at your website.

 

[marcok]

I mean the relay on PL 4000 for switched AC outlets .
On service manual rev . 6 81 it's written :
Note : the relay is not capable of switching power amplifiers
rated at greater than 250W / channel.
In other words : PL 400 yes and PL 700 no .
Infact I had problems with 700 and not with 700.
Ciao
Marco

 

[marcok]

A mistake ,sorry : not with 400 .
Ciao
Marco