ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi I'm new to this forum.
I recently acquired a beomaster 1900, something I had always wanted.Anyway this is a goodwill purchase so I have no history about this receiver.I didn't even power it up due to finding the output devices not properly attached to their heatsink. And tested the left channel output pair which are fried.I purchased output devices replacements for both channels. And plan replacing power supply caps and rectifiers.Continuing examination of the chassis and going through the schematic I found 2 areas on the bottom of the main board that kinda got scratching my head. At first I'm thinking this was a kludge by a tech.... but the components seem to be similar to others on the rest of the board.I'm putting this out asking if any one has come across these sorts of changes in a beomaster.Below is 1 of 2 snippets of the areas from the schematic that are affected. I'll post the 2nd in a follow up post.Thanks,Joe
--Joe
This is the 2nd schematic area.
That is zoomed in too close for me. Could you take a photo of the actual board and highlight the area you are questioning?
-sonavor
This is the TP17 area on the board:
This is the TP200 / TP300 area on the board:
Since I'm new to this forum I'm now wondering if I should have posted this on the workbench forum.
As of today I'm continuing replacing the electrolytic caps, measuring resistors, checking diodes and transistors, cracked solder joints.....
I have decided to revert back to the schematic on the TP17 resistor (3.3Mohm) to the -30V supply. This makes me think something failed in the 15V supply cicuit, which I will closely examine.
Lamps that need to stay incandescent have been checked. All others have been swapped for white LEDs.
Also harvested the "good" incandescent lamps for future use.
Thx for reading,
Joe
Well, that is interesting. On the 3.3Mohm resistor from TP17 to the -31 VDC rail it appears that was added to bring the Beomaster 1900 up to what the Beomaster 2400 has there.My Beomaster 2400 schematic shows it having a 2.7Mohm resistor between TP17 and the -31 VDC rail.The Beomaster 2400 is the same preamplifier, power amplifier and tuner design as the Beomaster 1900 except that the Beomaster 2400 has a remote control section.
TP200 & TP300 are the nodes where the selected source from the respective left and right channels show up and go on to the Beomaster volume control circuitry. So perhaps the mod there was to fix some problem regarding the source selection? Like I said, none of the Beomasters I have seen have that mod.We can ask Martin (Dillen here on the forum) about those TP200 & TP300 modifications.
Thanks for that reply.
I'll download the 2400 schematics and compare.
As for remote control I'd expect another board or more components (besides this 3.3Mohm). Although the board has "Remote Receiver" written in traces on the main board. Still the solder connection didn't have that factory look plus the resistor is mounted on the bottom.
Was it possible to convert from a 1900 to a 2400?
I looked at the 2400 schematic, agree about the 2.7Mohm pulldown to -31V but the unit I have doesn't have the remote board (#9). Possibly there was a board swap in the past on this unit???
I'm pushing onward. I've only replaced 2 resistors so far (out of tolerance, but higher than spec). Only transistors to be found bad were the left channel output pair.
The Beomaster 1900 and 2400 shared a lot of the same parts. It is common for the main board on the BM1900 to have the remote control area. I don't think it would be worth the effort to convert a 1900 to a 2400. You can pick up a 2400 so inexpensively that I would go that route if you wanted to have remote functionality. -sonavor
I was only suggesting that a board swap (by previous owner) might have been a possibility in my case.
Not really interested in a remote. I just want to get this 1900 up and running, I think it's gonna be so cool. If fact I really want to wall mount it, that's one of the nicest aspects of this form factor.
I would guess that is the original Beomaster 1900 board and a service center added the 3.3Mohm resistor as part of an upgrade. It isn't unusual to add a component to the trace side if it isn't taken too far.Check with Beoworld member and moderator, Dillen (Martin). He has some nice parts for the Beomaster 1900 like new feet for the chassis and new, plastic sliders for the slide controls (balance, bass, treble) to hold the contacts. It is extremely common for some of those to be broken. I think I have replaced those on every BM1900 and 2400 I have restored.
Also ask Martin about those components added to TP200 and TP300. He might have a B&O service bulletin about those.
Thanks for your replies, you are most helpful.
And I will send a message to Dillen, I want to understand the design idea of the tp200/tp300 edits on this chassis.
Thx.
I wanted to add a little more detail about the TP200 / TP300 changes I found (uploading a modified schematic showing the changes).
The change, to me, alters the DC (static) voltage ratio from ~4:1 to ~ 1:1 as seen from a TP200 / TP300 to ground perspective. Not certain how this affects the volume control (maybe an impedance matching idea???).
At first glance it doesn't make much sense.Are the LDR resistors in the volume control dying?Wrong lamp fitted in there?
Martin
I do not know if the photo resistor is going bad, that I will look into.
At first inspection the lamp in the volume down position was burnt out....I swapped that with a good one from the tone control / balance set, so the lamp set for the volume are good..... but will recheck.
Before reading your message I reassembled and powered up with a variac monitoring the 15 volt supply. Initially the good news the 15V supply was nominal, the relay kicked on about 70V AC and some touch controls work. I could not select the tape input for my test signal so will have to check my touch panel. So not sure about signal to output yet.
So I've some items to address.
Thanks!
Whereas the front panel lamps can indeed cause problems if not the correct type and wattage, they are not the ones I am talking about.I am talking about the lamp inside the LDR casing, that controls the volume and Loudness.
So I'm totally ignorant of the contents of that component. I just tried measuring R200 / R300 and read a charging capacitor....
Alright, that LDR component seems fine.
The lamp reads 18ohms
The 4 photocells read max resistance in absence of light but read 80 to 100 ohms when place near a light source.
Thanks Martin for educating me on that part.
Moving on to more checking.
After further checking I found that the balance slider is in fact broken...not allowing signal through to the main amp stage.
I took this slider apart and found the wipers were not fastened at the slider. The small plastic strap that holds the metal wiper in place broke...both channels. I fixed this with super glue (believe or not it holds really well, even after dexoit fader lube). But either the previous owner or me, while adjusting the broken balance slider caused the wiper to score the resistive material on the left channel.
After checking for possible replacements or parts I found that the main slider bodies are not made. Only "harvested" from donor beomasters. So in previous repairs to other potentiometers I have created a slurry of graphite and pro-bond glue....sort of a conductive paint. I "painted" over the scored resistive strip area where the scoring occurred. Left it cure overnight. It worked.
So right now doing initial burn-in of the beomaster 1900 listening to Robbie Robertson's "Music for the Native Americans".
I removed the 3.3Mohm resistor added to the TP17 node and -31V. And I plan on reverting the change to the TP200 + TP300 resistor divider network as well.
I'll continue adjustments, but this is cool, perfect addition to my Sherwood, HK, Luxman, NAD, Marantz and Sansui collection.
Thanks for all the help for a B&O newbie.
The broken tabs on the slider controls are typically broken on almost every BM1900/2400.
Martin provides replacement sliders with more durable tabs.
jhjove: I fixed this with super glue (believe or not it holds really well, even after dexoit fader lube)
I fixed this with super glue (believe or not it holds really well, even after dexoit fader lube)
That was what I initially did too.And, sad to say, what I recommended others to do.But the problem with the black plastic is its high oil content.The superglue losens, the wiper breaks off again and the glue remains only adds to the mess.Hence the need for reproduction parts (beoparts-shop.com)