Mission Pcm2 caps

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Disabled Account
Joined 2014
Hi All,
I've a poorly PCM2 which I'm trying to resurrect and have got two caps on the out put board which I'm trying to identify:
Would someone be kind enough to confirm these are BiPolar 470uf 6v and 47uf 16V? I looked on the internet but couldn't find a datasheet for these rodenstein caps.

Thanks in advance.
Joe
 

Attachments

  • IMG_2057.jpg
    IMG_2057.jpg
    758.3 KB · Views: 85
  • IMG_2056.jpg
    IMG_2056.jpg
    721.9 KB · Views: 82
Administrator
Joined 2007
Paid Member
Have you looked where they connect ? for example do they go to the opamp supply pins 4 and 7 of the NE5534 or do they connect to an opamp output (so could be a coupling cap).

Same for the other board, those look to be at the end of some low value resistors, perhaps an audio output coupling cap.

Does the 'dot' have any significance on the 470/16 type ? edit (470/6 type :))
 
Disabled Account
Joined 2014
Thanks for responding,

sorry but I've put the player is back together at the moment until I get some more time to work on it, so I can't confirm the connections. I wanted to change these out as the crazing is all over the tops of the '470' ones so it looks like they're way past their best. Although the main reason to look at the player was it is exhibiting odd behavior - it turns on for 40 seconds then powers down, I then a couple of seconds later - on it comes again , stays on, then goes off. It'll cycle like that for a while until you actually turn it off. I need to get some new 200mA fuses as this might be the culprit.

So while I had the hood up I thought I'd change some of the caps in preparation. I've had a look on the internet and this type of ROE cap is quite old.I think the polarised ones do have a + or - on them.

thanks again
Joe
 
Administrator
Joined 2007
Paid Member
They are old and they can and do fail. I've had experience of these on Quad amplifiers, a 303 I think from memory.

Pictures of old ROE caps do show a + sign but I wondered about the dot on yours and whether it signified anything.

First thing has to be to see what they actually do. Anything rail related is going to be a standard polarised type, signal coupling could be bi-polar.
 
Disabled Account
Joined 2014
Hi Mooly,
Ok the big caps are connected to the 2 op amps via pin 6. The smaller ones, these I have no idea on as the traces are very small and just go off to resistors. But this is definitely an output board.

Unfortunately there was some discoloration on the lower MAB Chip board, which required a new resistor to be fitted, I did a cap change at the same time and on replacing it I now have a bigger problem with no display (it's lit up on different segments) and a tray motor that wants to go in all the time. So more work to do - I wonder if either the chip has had it, or I've a transistor gone down on that board. Nothing on the internet apart from the unavailability of that MAB chip. Still I'll persevere with it and see it I can't get back to where I started. One thing - I checked the diodes on this board and one was odd, it only has B23 marked on it - its a small glass one, DMM on Diode check produces voltages ( component off the board) 0.7 and 2.3?
Thanks for your time
Joe
 
Disabled Account
Joined 2014
Thanks Mooly,
I'll have another look at it next week when I have more time, none of the regs on the board looked defective, but you never know. I checked the stocko's for continuity - no problems, and that's the only board I've worked on since I had full display and the switch off problem. Very odd. Its a real pain not having any sort of schematic.

Could you suggest a suitable replacement for the zener if needs be? There's nothing coming up on a google search that I can find.
Regards
Joe
 
Administrator
Joined 2007
Paid Member
I would doubt the diode (if it is a Zener) is faulty tbh. Without seeing a circuit it is hard to be sure but I would guess it could be a 2v7 type (2.7 volt). A DVM actually displays the volt drop between the meter leads when used on 'diode test' range and that is why diodes read 0.600 to 0.800 approx. (0.6 to 0.8 volts) which is the forward volt drop. A Zener would conduct in the other direction as well... so something low like a 2v7 seems plausible. It almost certainly is OK though.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.