3250 Update, Questions

USMC Spike

USMC Spike

Well-Known Member
I've finally gotten around to checking out the 3250 Preamp that I got
from another member here. It's pretty clean and I've got the service
manual for it, big disappointment.

I looked and didn't see any other instructions. None posted either,
that is why I ask. I've not worked on one of these before.

PJ01 Board Removal.jpg

I don't see three screw on that terminal board, in fact
I don't even see 0302 at all.

2. Do they mean the three screws along the bottom of the
rear backplane?

3. It must be, then there are two screws each along the
side and rear of the backplane (terminal board [0302]).
Then this just folds back.... It looks like it takes another
board with it.

QUESTION
Do the pins just slide out and will they go back in again?
It looks like they are soldered?

4. Remover the two screws at the bottom of chassis.

5. Looked for the clamp but didn't see it (0231)
and the bracket (0223) then, pulling pushing gently
slides the PreAmp board out from the front vertical board.?

The reason I ask is I read similar instructions to repairing a
laptop computer....some of the connects slid out from the
connector leaving just the flat wire. other connectors slide
out with 1/2 the connector.

I pulled the keyboard flat wire out...when I should have
pulled the other end of the connector. Thus rendering
the keyboard usless, because it can't be resoldered
reattached on the 4 layer board they used.

It does work with a USB keyboard and usb dongle. :)

My goal is to ID the componants, put it back together,
and listen to it for a while before replacing caps, etc.

Thanks,

USMC_Spike
 
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Catrafter just did a restoration on a 3250.
He mentioned that the three boards on his did NOT unplug from each other making it a pita to access.
I would send him a pm or he might see this thread.

Bob
 
I didn't read the directions, I just took it apart.
Removed the knobs and face plate.
Removed the front chassis, then the screws holding the boards to the rear panel and bottom chassis.
Kept the U shaped assembly of all three boards together.
YMMV

Tom

3250 rlyps (2).JPG 3250 rlyps (4).JPG e
 
Okay,

Thanks for the quick replys Bob and Tom.

I got it, the backboard is the backplane/chassis, and mine
will tilts out.

These aren't soldered together, the slide into and out of
the connectors. I don't know what it's called.

Wouldn't you know, now that I got bench apart
trying to install more shelves to make room for stuff
and need better work area...I had to desolder the
the blue wire. I think attenuator.

They used some good electrolytic is seems,
Chemi-cons
Elnas,
Orange Chemi-cons...those low leakages?
No BiPolars I see.

I"ll make a list and check the lead spacing on these.

Is there anything really special I should do while I'm in here?
Also, is there a better way to get the hot melt glue off the board?
It's only around the 470uF 63V caps.

While is apart, the stepped attenuator, it almost looks like a standard pot'
but with a piece that clicks....

One of the knobs comes apart, is that any recommened way to reaffix them
the black plastic with the aluminum? SuperGlue, rubber cement, goop,
nail polish? Just trying to keep it from spinning....cleaned with Iso.

Just want to check because there is that ONE part that when you put a
dab of Superglue on it, it disintegrates before your eyes.

Thanks,

USMC_Spike
 
Well it wasn't much of a problem to get it out.
cleaned everything up now I'll put it together
again and listen.

Cleaned out the ususal suspects, pots, switches and the like.
Wrote down all the caps and their lead spacing for ordering
replacements.

3250 Board Trace Side.jpg

Now I need a coffee to put it back in. And listen.
 

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So, I'm down an amp--actually three.
I have no room, so I pulled my Audio Research SP3A1
that's been highly modded, including a new power supply.

Put the 3250 in it's place, the only amp left working
that's ready to go is an old Citation II that I rebuilt
some 20 odd years ago. This one is tweaked a
bit more as it's running in triode mode w/KT90s.
My source is a lowly HK CD Player plugged into
the 3250 Aux with Pre Out into the Cit II, coupled
to a pair Klipsh Cornwalls, heavily modded.

I mean really, it is heavily modded, there is a piece
or 14 gauge steel epoxied to the inside back of
these cabinets. Sound trying to go through layers
of Steel, epoxy, wood? Ain't getting no bad reflections.

I wasn't expecting much from the 3250 though the until is clean
and been sitting around for a year and a half maybe two. The only
thing I did was swab the circuit board to get the gunk off
them, then clean the pots and switches.

Nothing fancy D5, D100, F5, MCL 5, Iso, MCL100.
Read also what a few of y'all had to say about why
some of you like it etc.

REVIEW
It's a good piece that 3250 is. It's warm musical,
and it's just plain easy. I've gone through the usual
disks that I would typically go through...

k.d. Lang is good for a few tunes,
then we've got follow up
Chris Rae -Texas, ZZ Top - Stockings, Govi - mood music,
Van Morrison - Moon Dance, Then we have the showdown
with Johnny Copeland, The Ice Man, Robert Cray; Then
moving on out west, we have the Tower of Power - Bump City.
Then just some jazz after that and some classical.

It's real easy to dial in find some very nice sweet spots.
For the ice man, I had to bump the treble up two...
He's playing the crap outta that Telecaster....
that Albert Collins is the Master of the Telecaster.
You gotta have that ice pick in your head
or it ain't working right. (it's not that nasty
horn Ice pic) even though these Cornwalls
have horns...they got the smooth duty horns
only made for a few years, these them ceramic hoans.
Mmmm mmmm.

This preamp really like's that CitationII.

Hmmm, I'll have to go dig out the old 8B
and slap some tubes in that baby and plug
her in for a ride too.

I always had to F**k with that ARC SP3A1 to
get it to sound right....

The 3250 is just so easy and nice.
It's why I went back to school at my
age, to really understand some of the
circuity and make it work. It's not like
I need another degree, but a little
associate's in Electrical Engineering
Technology don't hurt nun I reckon.

Them I be...
Walk down from Dallas, Texas,
down to Wichita Falls,
I got thinking bout that big legged woman,

Well you know how it goes.

Thanks TrannyMan!
 

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The 3250 was restored for a client.
I replaced all the electrolytic capacitors, film types (mostly WIMA) were installed in the audio signal path.
The old assembly glue was removed.
The tired voltage regulator transistors (on the small heat sinks) were replaced with new On-Semi TO-220 parts along with new thermal compound.
The suppressor network was replaced.
The controls were cleaned and lubed.
Every surface was cleaned.
The jacks cleaned, polished and treated.
The face and knobs cleaned and polished.
It was tested to insure it met or exceeded the manufacturer's specifications.

I think it came out beautifully, it sure sounds good.

Tom

3250.JPG
 
Tom, that is a fine looking preamp.

So, for one of these, would you recommend
what you did for your client assuming that it's
fulling functional?

I've got to do some more research before I start.
I assume to bring these up to speed and to last
for another 30+ years I should probably do the
same on mine.

I didn't see any bi-polars.
I was thinking to replace with similar caps
NCCs SL- with current UCC caps. Black
NCCs LR - Orange Capacitors...with ?
and the Elnas locations with Silmic IIs.

I could find small films for the 1uf, 2.2uf, and 3.3uf caps
IF they fit.

The two Vregs, on TO-220, heat sinked.
Q801, Q802, So it looks like these are
pass transistors used for volt regulation.
Not like the 78xx, 79xx nor the 317types.
Did you go with something like
the TIP41,42 or Mje15032G?
Hmmm maybe the MJE as they were Motorola derivative?

How does the rest of the circuit like them?


And our friend the suppressor network,
looking that must be G001, the 0.1uf + 120 Ohm Resistor
Is that all in one package?

Tom, if you don't mind sharing,


Any other recommendations would be appreciated.

I haven't pulled anything yet, but as I went through and measured
lead spacing.

This is good stuff.
 
Spike,
I like to use WIMA or Panasonic ECQ for film caps in the signal path. Sometimes you have to bend the leads slightly to match the spacing on the board.
One of the Vreg transtors is an NPN, the other a PNP, I used MJE15030 and MJE15031.
They work fine as Vreg pass transistors and have a higher Vce, 150V. On-Semi acquired Motorola semiconductor quite a while ago, get parts from a reputable supplier.
For the suppressor you can buy one with the resistor built in, but I usually just make my own out of a interference suppression type film cap (300VAC) and a 120Ω 1/4W resistor.
The 3250 is a good preamp, one of my favorites.

Tom
 
Thanks Tom,

Yep, I didn't ID both, but I have the datasheets here from on semi.
Vceo/Vcb @150V...can't hurt, vs 120V.

I Always try to get parts from Standard Distribution Houses and/or
known good sources. Go Figure.

Have a healthy stock of ECQs as well.
as well as others.

So I just finished up my final EE Tech course
at the Community College have 3 other classes
to go. I have to see what will transfer to a 4 year
place as I like this stuff.

That said, I haven't learned about the pass transistor
used for voltage regulation. After I get all the parts
I should make some Measurements of the unit before
I replace caps and such.

Is my assumption correct that I should leave the other
transistors alone if the PreAmp is working fine?

There is barely any noise from it as it is.

One final question how well do these fujitsu relays
hold up? Are they the 6,000 switch variety or
of the million type?

I'll look it up and see if I can't find it.

Thanks,
USMC_Spike
 
I change the pass transistors as a prophylactic measure.
The Fujitsu reed relays usually last a long time, which is a good thing as a suitable substitute is difficult to find.

Tom
 
Hi Tom,

That is what I was thinking. Even though they might not need to be
replaced...Better to be safe with new units, i.e., MJE15030,MJE15031.
How would the LM317 & LM337 work here?

Thanks

USMC Spike
 
Do y'all know if the from the phono in
on this pre amp, if Marantz has it cross
over to the the other channel, like some of
the Xs that I've seen in in pre amps?

3250 Service Manual: LINK

If I start from page 10 (8. Block Diagram) pdf p12
which shows
"From RIGHT Channel, to RIGHT channel,"
in the center of the page, in stereo mode.

Then on page 9 (7.4 Front Panel Assy) pdf p11
So the right channel goes through JS02-1//JJ05-1
and trace the circuit through to:
SJ03-3: SJ03-1 to SJ01-5 which goes through
phono pre-amp assy switched at SJ01-1
to JJ01-1 which is the LEFT Channel Phono input.

I'm going through this switch-ology to identify the
components in the various signal paths.

Looking to upgrade some of the other parts if needed
down the road.

Anyone notice that? Or am I off base here?
I missing something?

Ideas?

Thoughts?

Thanks,

USMC Spike
 
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Following your thread as I have both a 3250 and 3250B that have not been “refreshed”. Need to finish my 170DC 1st.
 
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