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
Not all is well...........replaced the D204 & D205 diodes and was disappointed, still no mV on the emitter resistors as I was hoping, however the overload lamp has stopped coming in and the left channel still continues to work fine. Next up will be the Zener Diodes D202 and D203. I do have power on the +35 and -35 rails so will need to follow this through. Such fun...........
I'm still waiting for parts to pursue mine but having the same problem where I can't adjust the bias on the left channel.
Curious to know if changing the zeners will cure the problem!
I choose the modern equivalents 1N52242B & 1N5223B but i prefer to have all the parts in hands before changing them.
I'll stay tuned to see how it turns out with yours.
Ok....I've just spent over four hours testing and measuring voltages, comparing readings from one channel against the other and could not find any significant differences.....so frustrating. I also replaced the two zener diodes to no avail, eventually sitting glaring at the damn thing and uttering oaths it dawned on me that when replacing the emmiter resistors I had soldered them both into the board in the same orientation, not a problem functionally....however you cant measure the 5.4 mV unless your across one of them.....with them soldered in the same way around I could never measure jack ***!
swapped one around and bingo.......off to bed now.
connected spotify via Tape 2 and injected a track, left channel great right channel not so great....bit of probing around revealed a loose connection on one of the plug and sockets at the input to the right channel......bit of jiggling and the right side is now singing like a bird.Will need to bottom put the poor connection thing but as I'm going to recap the whole thing I wont worry about it right now. Changed to big power supply cans and also the quiet current trimmer, will need more parts to complete.
Just had to share these.....surely it would have been easier just to buy a couple? love it ;~)
Good for the museum!
As I'm waiting for the postman I have started to look at the case, decided on a walnut burr veneer for this one.
As I was testing the left channel I noticed the output transistors seemed to be getting quite hot for such a short power up duration, in particular OTR100.....didn't think too much of it and I'm certain, or thought I was certain, that when I originally attempted to set up the quiet current on the left side I was getting the 5.5mV across the top of the two emitter resistors and it did appear to respond to the trimmer being adjusted.....but now that I look closer at this pair of resistors they are actually installed the same way around as the right channel resistors which wouldn't allow measurement of the prescribed 5.5mV. Looking at one of my functioning machines shows the left two resistors installed in opposition too......I suspect our DIY chap may have removed the right hand side of these resistors and just replaced it back to match the other one, I will reverse it before I power up.
This is a pic I posted from the Basket case exercise some time ago.....clearly shows the orientation of the left channel emitter resistors.
Craig:the orientation of the left channel emitter resistors
sorry Craig but direction of a wire-resistor is irrelevant. Must be something else...
hx
Hemenex.....thank you for your observation, however its not the direction of the resistor that creates the problem, its the orientation of the resistor in the board that is the issue......this simple diagram identifies the measuring points for the idle current mV (the tops of both resistors) and as can be seen with them in this orientation your measuring across a piece of wire.
However...if we rotate one of the resistors through 180 deg we find we are now measuring across one of the emitter resistors and not a piece of wire, I had to look long and hard at this too......
Craig,
after all you have shown here I couldn't imagine you would not be aware of such a simple issue
Anyway you made me dig out my defective BM4400 I have as spare and have a look into it.
If you look at the printing on the PCB you'll find this:
E of IC101 goes to the "in picture upper" (unaccessable) sideof R179 while E of IC102 goes to the "upper" (accessable) side of R178. So measuring the 10-15mV across both resistors has to be upper left to upper right of the resistors..
You could more easily use the open wire of the right resistor and the emitter of IC101 at the orange wire to measure the mV's according to the service manual.
Sorry for having been confusing
P.S. I own a technical product information of BM4400 type 2417 which explains (among other topics) the function of the power amplifier on 11 pages but it's in german.
Hemenex
No worries......I just prefer to measure from the tops of both resistors and look for half the recommended mV signal, thats a very good picture of how the resistors need to be installed to permit this, incidently....I dont suppose your spare BM4400 has a power switch you dont require?
Craig ;~)
Took a wire brush to the bottom plate to get all the rust removed, will need new feet also...ordered 4 similar ones from ebay.
Coat of primer ready for a matt black spray, had to sacrifice the dismantling instructions....but I think I can live with that ;~)
Craig:I dont suppose your spare BM4400 has a power switch you dont require?
Ain't that the same one as in BM3000 / BM4000? Then chances are rising...
hemenex: Craig:I dont suppose your spare BM4400 has a power switch you dont require? Ain't that the same one as in BM3000 / BM4000? Then chances are rising... hx
Sadly it isn't.
Martin
Yes.....I know this, I have a 4000 removed the case and bottom cover to have a look ;~)
One will turn up in the fullness of time I'm sure, scary thing is it may come with a complete bank of switches and require the replacement of the whole set....it does not look an easy task replacing just the power switch in isolation either! (how hard can it be?)
You may want to look if you can fit this type of switch instead? There is a bunch of different models available at Mouser and maybe one would fit. You will have the ON/OFF function but you will lose the input release switch mechanism...
Dillen:Sadly it isn't.
Are you sure?
BM4400 mechanical parts list pos. 45 mains switch # 7450010
BM4000 mechanical parts list pos. 90 switch # 7450010
BM3000 mechanical parts list pos. 89 switch # 7450010
or isn't that the switch we are talking about? What am I getting wrong here?
I know you are the expert...
Correct for the early version of Beomaster 4400.The switch was changed (together with the rest of the switch row, the potentiometers, the tuner front-end and a few other things) from s/n 1524001 to a different type.The old and new parts are not interchangeable:https://type181.files.wordpress.com/2014/07/7450010.jpg
Ok then as my BM4400 type 2417 SN starts with 1424... and that proves it's an earlier one. Its switch looked equal to BM3000. What about craig's SN?
Did they change the type number on redesign? I don't think so.
Thanks,
oops, should have read the whole thread where the different mains switches were already mentioned. But couldn't find craigs SN.
My power transistors are mounted in a different style; looks more like a plastic screw instead of the nut in Craig's pictures Does this point to a newer SN?
Ok.....serial No for my latest endeavour is 1601023, the weather has prevented any deliveries of the bits and pieces I have on order to progress so I have spent a little time looking at the darlingtons I removed, I acquired this transistor analyser and thought I would give it a run out.
I bought this analyser a while ago; very useful tool!
It certainly would appear so.......it provides a huge amount of information about the device under test when connected to the laptop, unfortunately almost all of it means little to me given my current level of understanding, I need to condense the information down to the meaningful parameters, the ones that identify if the piece is good to go or not......I think comparing the readings with the published data sheet is a good place to start, any member opinions are welcome on this ;¬)
The values important to me are the HFE and the leakage.
HFE where for a given transistor, the value must meet the minimum requirement of course. Also, when they are pair matched, I'm trying to match them within 10% to avoid one working harder than the other. It is also preferable to balance right and left channel HFE... but not always possible unless you change them all...
Leakage, well you don't want a transistor to leak current when it is not supposed to...
Craig: I may have a working switch for you. I have a newer model BM 4000, bought for spares, newer tested it.
Collecting Vintage B&O is not a hobby, its a lifestyle.
BM4000 never used the newer switch.It's unique to the later BM4400.
Søren Mexico: Craig I have a BM 4400 coming in after Xmas, bought it for parts, maybe the top cover is better than yours, the top free to go for shippingcosts
Craig I have a BM 4400 coming in after Xmas, bought it for parts, maybe the top cover is better than yours, the top free to go for shippingcosts
I was hoping Soren was referring to this BM4400 and not a BM4000
;¬)
Craig: Søren Mexico: Craig I have a BM 4400 coming in after Xmas, bought it for parts, maybe the top cover is better than yours, the top free to go for shippingcosts I was hoping Soren was referring to this BM4400 and not a BM4000 ;¬)
It was a typo, of course I mean BM 4400, let me check this weekend if it works.
Soren
That would be great, some pictures of how you get it out would be appreciated too
Craig: Soren That would be great, some pictures of how you get it out would be appreciated too
Will do, stay tuned tomorrow
plywood shapes arrived today, had them cut to the overall size but without any shaping....
Cut the front chamfers and marked up the cuts to allow the cover to slide ober the protruding screws of the chassis....
bought this snappy little accessory for the dremel.....router attachment, never used one before so was a little nervous.
Overall, and considering no one will see it, it turned out quite well......will need to start the veneer exercise as soon as I have softened and flattened it out.
Craig: bought this snappy little accessory for the dremel.....router attachment, never used one before so was a little nervous.
I like that, good for these small cuts, I have a big router that came in handy for some speaker frets
Craig, was just about to start on the BM 4400, got visitors, will have to wait until tomorrow