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, my first post here, as lat week I became a B&O owner for the first time. I bought a Beomaster 5500 with the Beogram CD5500 and a set of CX100 speakers off ebay locally.
The Master Control Panel had suffered severe battery leakage - the owner gave me a Beolink 1000 remote too so I can use the system. So far I'm impressed with the tuner's quality, although the CD playback isn't quite as good as my regular stereo setup (Audiolab amp and good Rotel CD player). I'm happy with it, and will be working through a symptahetic restoration, and possibly adding some panel speakers (beovox 3000, or maybe older P45's), to use the Beosystem in my office.
While I wait for new speaker foam from goodhifi for the CX100 speakers, I've turned my attention to resurrecting the MCP.
So far, I've:
The good news is that now, I can power up the remote, and it talks to the Beomaster 5500. I can use it to change inputs, presets etc. and most of its display is working!
The remaining issues are:
A quick examination of the main circuit board for more corrosion damage has found a couple of diode's along the bottom edge with leads which are not attached (due to corrosion). The other diodes on the board all test ok with a multimeter
Does anyone have a service manual which details the parts of the MCP5500?
I'm after the details for diodes D7 and D30 for now, and probably more components as I progress to more serious circuit tracing and
I'll try to work out how to add pictures so you can see the horror I'm trying to overcome :D
After careful examination of the board, it appears the diodes in question are plust regular diodes, and not Zeners. I'll add a couple to my next electronics order from Mouser.
In the meantime, here's the pics of the carnage that D-cell leakage can cause to an MCP!
Dom
2x BeoSystem 3, BeoSystem 5000, BeoSystem 6500, 2x BeoMaster 7000, 2 pair of BeoLab Penta mk2, AV 7000, Beolab 4000, BeoSound 4000, Playmaker, BeoLab 2500, S-45, S-45.2, RL-140, CX-50, C-75, 3x CX-100, 3x MCL2 link rooms, 3x Beolab 2000, M3, P2, Earset, A8 earphones, A3, 2x 4001 relay, H3, H3 ANC, H6, 2014 Audi S5 with B&O sound, and ambio
Eww, that's ugly. Good job getting that far. These seem rather robust technically, so if you can repair obvious damage I believe there's a good chance you'll get it fully operational as long as the processor itself is fine.
The service manual for Beomaster 6500 includes the schematics & PCB pictures for the MCP (5500 and 6500 are, as far as I know, pretty much identical internally). That is on site for silver & gold members.
Meanwhile, those two diodes are bog standard small signal diodes (1N4148).
Does the MCP wake up when you try to turn the wheel? If not, the problem is in the switch contacts that make when you turn it or related circuitry. If it does wake up but doesn't do anything more from the wheel, you will need to replace the associated opto sensor. They sometimes fail even without any apparent reason.
D7 is associated with the wheel switch (so that could explain that fault) while a failed D30 will probably partly disable the keyboard.
If you make a list of what display segments are out, we might have a ballpark guess at the fault location. The display LEDs and 7-segments are driven in the typical matrix fashion, and each row & column has a driver circuit with one or two transistors.
--mika
Thanks for the interest!
I replaced the diodes with the smallest ones I could find at my local electronics shop.. the black/silver one in the bottom right. The other components in that corner test ok with a multimeter, so I'm leaving them as-is for now despite the corrosion.
And here's the film resistor I used to replace the broken one.
And here's the repair of the bottom two traces which got hit by the corrosion too. They test cleanly with a multimeter for continuity, with no continuity to adjacent traces/component pads. A few of the pads have broken due to corrosion, but most have at least some copper to solder to.
After replacing the obviously broken components, there's still no change in the core issues. As they stand, the problems are:
1. Volume wheel doesn't work
I took the contact switch off and cleaned it throughly - it tests ok now. When I turn the volume wheel, I get continuity on the pins of the 3-pin connector. Unfortunately, the wheel doesn't wake up the MCP, so the problem is somewhere inboard of the 3-pin connector on the logic board, which isn't a huge surprise, given that its positioned right in the corner which had the most visible corrosion when I first took apart the MCP.
I can confirm this by the fact that shorting the contact pads for the 3-pin connector on the board doesn't awaken the MCP either.
2. Segment 2 of the numerical display doesn't work (with 1 being the right-most).
3. Track/preset number blocks 1-4 and 9-12 aren't working.
Here's the display lit up on radio (frequency is 95.3 - the 5 digit isn't working), and showing the clock.
Note individual segments of the working digits all seem to be there - I checked at various times to make sure.
As far as I can tell from fiddling, everything else is working - I can set the clock, play radio/cd, switch inputs, scan FM frequency (along with animation on the level meters), etc. which is good news, as it implies maybe the processor is okay, and its just a few items which aren't working. Even the dreaded Mute relay works correctly.
At this stage, the biggest suspects are the transistors, both on the display LED board (SMD 1K transistors), and on the main logic board.
You seem to have used rectifier diodes 1N400x - I guess they should work in place of 1N4148 in an application like this, but I'm not completely sure.
The service manual doesn't show designations for the separate LEDs so I'm not sure which ones are missing on your MCP now, but if the 2nd from the right 7-segment digit is completely out, I guess one of the strobe driver circuits is not working (apparently TR31/TR32 and associated components) and would disable many of the other LEDs as well. This is where you would really like to have an oscilloscope and the schematic. Compare to the neighbouring similar circuits, there are five of them.
Thanks Mika,
I've been away on holidays with the family, so no progress for a month. Back now.
Agree that having a schematic would be ideal, but you're right, comparing to the other circuits is a good start. My electronics knowledge is pretty limited - did some in high school about 25 years ago, so I might have to get myself a book on the subject and learn more.
I'll see about borrowing an oscilloscope off a friend - being able to trace the signal through the circuit would be a great start!