HELP! Rescuing Dad's old PL400 S2 (pics)

[kevin]

We'll... you did a good job Brad !!! I been following this thread since ya started it.. I hear that Lee guy is pretty good with these things.... Take your time and get that amp right !!!! You have only just began with it.... Put all the new boards in it.... You will be glad you did !!!

 

[lightfall]

Thanks man, it is really tempting. I am hooked on audio again. It has been a while since I had a good amp, so when I got those bookshelf speakers hooked up to the PL400 last night I set them up and sat down and listened in front for about 20 minutes. I forgot what good sound and stereo imaging sounds like. I just sat there absorbing it. I listened to Orbital - "In Sides", which is a really well mixed album and really tests speakers. It was a real pleasure, and I am looking forward to getting everything up and running in top shape. I have some upgrades to do to the amp too which I am really looking forward to hearing the before and after!

Now for this pesky preamp...

 

[lightfall]

Gadget, I think one of the boards might be supported by the base of the pots. I have to take a close look and make sure there isn't a fracture in the solder in the difficult to observe base of the pots as they connect to the PCB. That makes some sense since the weirdness did not start until I touched the tone control. The tone control button was seized up, and I did deoxit until it was free, but perhaps I did not clean it enough.

I dug up the 2000 service manual, and it does not appear to have cards like the 4000 has. Thats a good thing, fixing that thing was a huge pain in the ass.


http://thecarversite.com/shell-manuals.htm

iff'n you'd like a copy of the manual for that. The owners manual and the service manual are both there.




These are the guts of a 4000. You can see all of the cards.

here's the bottom side. The one I fixed needed ALL of those joints re-soldered. The cards are not supported, so they put a lot of strain on the main board.

 

[laatsch55]

There are several threads on restoring the 2000's....might be handy...

 

[lightfall]

Yea, fun times 2.0. I have to exhaust existing knowledge and troubleshooting before I start posting new questions. I have the service manual now so I am going to be going through that sequence.

I have to get this preamp working so that I can use the amp with phone and switch between that and my DAC for FLAC files and so forth. I am also really interested in upgrading those components on the amp, BUT I want everything in working order before I start modifying!

 

[laatsch55]

Yep....

 

[lightfall]

Power on amp hooked up to speakers and DBT: OK and plays music.

Power up preamp to DBT: OK.

Amp to DBT: OK.

Preamp and AMP to DBT: OK.

Preamp and amp connected by RCA wires DBT: OK.

Preamp and amp connected by RCA wires left speaker wired and /or right speaker wired and preamp OFF DBT: short and buzz.

I then unplug RCA from the preamp to amp and turn off preamp either speaker still wired DBT: short + buzz.

Completely unplug preamp and rca cords and just leave the amp hooked up to speaker wires DBT: short and speaker buzz.

Finally leave just the amp attached to nothing but DBT: OK.

Restart with amp to speakers and rca in from my phone: OK on DBT and with music.

I am struggling to understand this.

I checked for shorts then per the service manual on the PL2000s2 and got connectivity chassis to most wires, rca inputs and outputs, on the preamp. I see no shorts anywhere.

 

[lightfall]

Additional test: after using just the amp to mp3 to speakers on ac to play music if I unplug from ac then test on the DBT it will short. If I then unplug the speaker wires it will stop showing short on the DBT.

 

[laatsch55]

Not much of this is making sense.

1.--When the amp is on and has speakers hooked up WITH NO PRE AMP on the inputs it will be VERY noisy.

2.-- When you unplug the amp the power supply capos discharge through the board and outputs and can have significant DC offset on the speaker outs...

As to the rest of that.......it appears the pre has some problems, or your interconnects...

One last thing....the 2 resistors and cap on the speaker posts...do the resistors look stressed?

 

[laatsch55]

You can now keep the DBT off the amp. It can not behave itself as an amp going through the DBT when the amp is hooked to speakers...

 

[lightfall]

I only played music with speakers with the amp to AC. Should the speakers buzz and the DBT activate with no music playing or should I not have plugged the speakers in while on the DBT even with no input plugged in?

 

[lightfall]

I don't see why the DBT should show short if the preamp and amp are plugged in and speakers are plugged in with the preamp off and no music playing, unless a DBT will always activate if an amp is plugged into it with speakers hooked up.

So the DC going into the speakers with the amp recently powered off will cause the DBT to show short and that should not be concerning?

Should I show connectivity between the chassis on the preamp and the RCA inputs/outputs of the pre or am I correct in thinking this demonstrates a short somewhere that is likely causing the DBT to blow.

 

[laatsch55]

I would not plug or unplug either inputs or outputs on either with the units powered on....too many surges ...

 

[laatsch55]

I don't see why the DBT should show short if the preamp and amp are plugged in and speakers are plugged in with the preamp off and no music playing, unless a DBT will always activate if an amp is plugged into it with speakers hooked up.

So the DC going into the speakers with the amp recently powered off will cause the DBT to show short and that should not be concerning?

Should I show connectivity between the chassis on the preamp and the RCA inputs/outputs of the pre or am I correct in thinking this demonstrates a short somewhere that is likely causing the DBT to blow.

The speakers represent a load, however small , but bias goes up and the outputs are loaded. Bulb SHOULD burn brighter...

 

[lightfall]

I powered off for a minute before changing ANY connections.

 

[lightfall]

When I say DBT shows short I mean I get a BUZZ and that 100w bulb is bright and does not settle down after a few seconds.

 

[laatsch55]

Good habit there Brad..

 

[gadget73]

If its humming, its drawing current and that will make the bulb light. Usually hums are flaky cables, but it might be a problem with the preamp. Try turning the level knobs all the way down on the PL 400 to see if it stops making noise. if thats quiet, then the problem is outside of the amplifier.

 

[lightfall]

Amp hums with the volume all the way down. It also hums with the amp knobs fully down and the preamp powered off. It also hums after playing the amp and then shutting down and rechecking on the DBT with speakers hooked up.

 

[lightfall]

Is there a cap or something in the amp that will just bleed after being shut down extensively enough to drive the woofers out a half inch with no sign of settling down?

I am going to try to play an mp3 through the preamp and see if it plays only on one channel again.