Terminal battery drain, BM 6000

My 80’s Beomaster 6000 remote control terminal is draining 9v batteries very quickly.

 

I’ve disassembled, cleaned contacts, reflowed all the solder points on both boards, except on the processor (trying to be gentle on that as much as possible). Replaced the 2 47pf capacitors. Removed and tested the BC328-25 transistor with my peak tester, good.

 

I’m still getting 40-120ma draw when hooked to my bench power supply when no buttons are being pushed. My terminal remote for the BM8000 has 0ma draw when idle. Each switch when depressed shows a 20-40ma additional draw when pressed (just like my working terminal for the 8000) and the BM shows no sign of any buttons being held down and the remote works as intended with all switches. Just kills the batteries.

 

 

I’m not sure how to diagnose this problem. Only thing I can think to do next is to try swapping parts between the 6000 remote and the 8000 remote.

It's quite common for the keyboard printed circuit to become conductive between tracks.

You will need to peel off the black tape,remove the contacts and clean the board with ipa etc.

In some cases,I've even had to score the board between tracks to overcome this problem.

When you reassemble,you can use Sellotape to secure the contacts,this seems to work well.

Nick

Thanks for reply Nick. Two more baths and scrubs of isopropyl and magic eraser alcohol scrubbing. Looks beautiful but still getting 100ma of current when at rest.

When you score the board between tracks, are you basically just scrapping all the top layer off near all the tracks on the side of the contacts?

Yes..They seem to be vulnerable where tracks are routed under the contacts.I usually use a pin or needle,to score with.The pcb actually seems to become conductive?You might expect this with high voltages,but not here?

You may be able to narrow down where the problem is by measuring the decoder lines back into the chip(pins  3-10 of  IC1)?

In standby,none of the lines should be active,but I think you will find that one of them is permanently high?

Alternatively,simply monitor the current being drawn from the battery,while scoring around the tracks,until it drops?

Nick

Fingers crossed, I think the problem is fixed.

While starting the scoring on the PCB with the switch contacts the current draw went up to 200ma and the R3 resistor on PCB 13 with the processor started getting warm so I moved my attention there.

Every bit of scoring I made around this area changed the current, even accumulation of dust would cause fluctuations. The scoring shown in the image is probably more drastic than needed but it was so fickle in how it responded to the scoring I got a bit over zealous.

I scored a couple points on the contact board too. But the work around R3 seemed the most effective and this seems to be working. 36 hours with the 9v battery showing no decrease in charge.

Thanks Nick, I wouldn’t have thought to look or try this.

Interesting indeed!

This phenomena is obviously something to do with the composition of the pcb?Or it could even be the residue of old soldering flux?

I think they used something called paxolin back in the day?Pcb's nowadays seem to be made of a fibreglass type material

It's one for the "gremlin" book certainly,and can save time when looking for culprets for those odd little faults that we encounter with vintage gear!

Thanks for sharing.

Nick