Author Topic: PF-6 circuit trouble ? (Read 593 times)

room037 · « **on:** June 03, 2009, 08:09:10 AM »

Hi Mica,

Finally I got 75' 145 SSB.
But unfortunately Bridge PU sound is very weak than Neck PU.
I think Bridge PU was dead at first.
But both PUs are OK with another PF-6 card.

Now I am thinking following troubles.

1: First possibility is disconnection. (But I can hear the weak sound.)
PU conector cords are repaired, but these are poor soldered. (I will up the pictures.)

2: Second possibility is the operation amp trouble.
Weak sound means no amplification on the PF-6 card.

Please guide me next step.

Eiji

JimmyJ · « **Reply #1 on:** June 05, 2009, 12:13:13 AM »

Hi Eiji,

Even if the bridge pickup is shorted or unplugged there will be some sound from that output because of the hum balance mix... I'm sure you have tried adjusting the output trim pots.

Your next simple test could be to swap the bridge and neck pickup inputs to the board (markings: T = treble or bridge pickup, H = hum coil, and B = bass or neck pickup). This should reveal whether the pickup or the board is malfunctioning.

If it's the card, then the op-amp chips are interchangeable and you can try (carefully) swapping them around. I would switch the TWO final output pair first and check to see if the problem has changed sides. Then try the pair closest to the T and B inputs.

These tests should help you isolate the problem. Obviously the connectors themselves could be the problem...

Good luck! Let us know what you find.
Jimmy J

gtrguy · « **Reply #2 on:** June 05, 2009, 09:22:03 AM »

On a card that old the chips are soldered onto the board, I think.

Bye,
Dave

room037 · « **Reply #3 on:** June 06, 2009, 08:22:03 PM »

Hi Jimmy,

Thank you for your kind words.
I am very surprised to the answer from you.
You are my Bass hero for the last quarter of a century.
And now I love the narrow 5 strings basses like you.
I wrote some topics on your thread, but I am too shy when I saw your post.
Always the hero rescues us from trouble.

Now the trouble of my bass,

PU swap test and PF-6 card swap test were done.
The bridge PU sound is OK through the neck circuit under PU swap test.
Both PUs are OK with my 76-421's PF-6 card.
Because bridge preamp section is malfunctioning on 75-145 card.

Dave's comment is right.
Old PF-6 card has 5 Harris 911 tips that soldered on the board directly.

Please look this pict.

PU connectors are resoldered, but not holded.
I think the card will back to mothership and needs repair work by daddy.

Eiji

(Message edited by room037 on June 06, 2009)

JimmyJ · « **Reply #4 on:** June 06, 2009, 09:35:50 PM »

Eiji-san,

I'm happy to be here and talking shop with my fellow Alembic brothers and sisters! Of course, as Dave pointed out, my suggestion about swapping chips only works on newer boards with sockets. Sorry about that.

It's good that you were able to determine that the pickup is OK. And it's hard to imagine the reason for that rough looking soldering job. My guess is that the shield for the bridge pickup lead broke off the board and the quick fix was to re-solder it to the exposed hum shield which was still connected. That should have worked, but the rough work is most likely the source of the current malfunction.

If you or somebody you know is handy with a soldering iron you could attempt to repair this connection by cleaning the original solder points of wire and solder (circuit side), trimming and preparing the old wire and reconnecting it all. Since it's not working now, you haven't got much to lose by trying!

Otherwise, you can send it to Santa Rosa HQ for a repair or simply order a new board with adaptors which will connect the old pickups to the new connectors.

Good luck! You have a nice collection of instruments!
Jimmy J

terryc · « **Reply #5 on:** June 07, 2009, 12:11:33 PM »

Sh*t..that is nice bass, I would get upgrade as jimmyj suggests, with an instrument that classy it is well worth every dollar & cent(pound and penny in the UK LOL)
I bet it sounds great with the upgrade..go for it man!

gtrguy · « **Reply #6 on:** June 08, 2009, 08:55:53 AM »

Get a VOM meter and check for continunity of the grounds from the pickup leads to the board. You should be able to poke the VOM lead into the connector outer tube and then touch the back of the board where it should be getting a good connection with the other lead, using the ohm setting. Kinda looks like a bad hum pickup ground from the photo?

Bye, Dave

room037 · « **Reply #7 on:** June 10, 2009, 09:29:17 AM »

I did the check for continuity of the grounds from Bridge PU connector.
It's OK. The soldering is poor, but it's still under connecting state.
This means the trouble is not connecting issue.

How much is the price of new PF-6 card, If I order it ?
I wish to repair original circuit, but If it's lost while the shipping...

Eiji

JimmyJ · « **Reply #8 on:** June 10, 2009, 12:12:54 PM »

Eiji-san,

First we must clear something up... Your original post said the trouble is with the bridge pickup, yes? The reason I ask is because the bridge pickup, which Alembic marks T for treble, is the FIRST input on the board, furthest left, with the red mark. So it could be that the questionable soldering job is unrelated to your problem and only there to distract us!

Fire up the bass with all 3 pickups unplugged but the pickup selector on both and the volumes up (not too much volume on the amp though!!). Then using the lead from the bass pickup as a source, connect to each input one at a time to see if you hear audio. All 3 inputs should pass some audio. This will at least determine which channel we should be concentrating on!

Let us know what you find.
Jimmy J

room037 · « **Reply #9 on:** June 13, 2009, 10:28:13 AM »

I correct to terms of Alembic.

Yes, trouble is T(red, bridge) section.
Please look this.

Point No 3 is part to soldring point.
It's a earth point for B(green or blue, neck PU)
But it connect to point No 2, and it is functioning well.
Point No 1 is swinging and unstable, but it is connected by connecting chcke from T connector sleeve to point No 2.

When I checked the circuit and PU connection at first, poping noise was appeared by touching T connector.

Today I got good news from my Alembic fellow in Japan Toshiaki (as to 81 0190 on here).
He will supply his spare PF-6(B ?) card with coaxial connectors.
Thanks Toshiaki !

Original PF-6 card will be back to mothership for repair ASAP.

Eiji

JimmyJ · « **Reply #10 on:** June 13, 2009, 03:04:58 PM »

Eiji-san,

Thank you for the further explanation, now I understand. It took me a while to realize the rough soldering was NOT the channel with the problem...

And with the help of your friend Toshiaki you have found a great solution. (Alembic users are a good family!)

Headquarters will find the best solution to get you up and running again. It's a lovely bass and worth the effort!

Seeya,
Jimmy J

room037 · « **Reply #11 on:** June 13, 2009, 07:14:43 PM »

Mr. Jimmy,

Thank you for the guidance.
I am very pleased to communicate with you.
Please call me Eiji.
I hope to do many conversation with you, about your music, 5 strings instruments (of course the narrow neck !) and equipments.

Dave, Terry,
Thank you for your advice.
I will up the info. after the repair work.

Alembic family in Japan, Eiji

mica · « **Reply #12 on:** June 14, 2009, 01:20:42 PM »

Eiji- Let me know when you are sending the PF-6 card so that I can be expecting it. Thanks!

room037 · « **Reply #13 on:** June 15, 2009, 03:32:43 PM »

Hi Mica,

Thank you for your reply.
Now I am waiting for the card from Toshiaki.
I will send it after fitting test.
Please wait for a while.

Eiji

room037 · « **Reply #14 on:** June 16, 2009, 11:19:20 AM »

Today I got new PF-6B card from Toshiaki.
Thank you !

I ask about fitting rigs of card on the backplate.
These are fixed on the card.
But new card has no fitting rigs.
Please let me know the tips for fitting.

Eiji