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JPF

Member Since 04 Nov 2013
Offline Last Active Dec 06 2013 10:19 AM
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Posts I've Made

In Topic: D150- One Channel Down!

06 December 2013 - 10:17 AM

Ah, today I am laughing. Those of you who have read the above know the story, but here's a synopsis anyway:
My old D150 broke. I started a thread here in the hope of getting advice on fixing it, where I lamented that the schematics and PC layout diagrams on the Crown site are illegible. After pulling out a lot of hair, trying to decipher the scans, I got a tickling sensation telling me that I may actually have those diagrams somewhere. Now listen, I am chaos personified, but I swear, I found an ancient copy of the amp's schematic in an old carton full of miscellaneous mixed papers within seconds, as though some mystical force were guiding my hand. Wit that and a lot of patience, I was able to more or less re-draw the PC layout, so that I could begin troubleshooting. But I wasn't so sure that my drawing was accurate, so I began with some trepidation.

Now I'm getting to the punchline:
Yesterday, I had occasion to look through that same box of old papers, for something entirely unrelated. This time I got all the way down to the bottom of the box, and what did I find there? Ha! The rest of the Crown document, containing parts lists, blowup-drawings, and two lovely, pristine drawings of the PC oard with all its components. Here's links:

http://www.flickr.co.../in/photostream
http://www.flickr.co.../in/photostream
http://www.flickr.co.../in/photostream

The link to the drawing that I made myself is now dead, because I'd hate to have anyone burn up an amp as the result of some mistake I made...

Now then: I STILL haven't found the problem in this amp. I have done a lot of checking, and found the following: No DC at output. I've checked output x-sistors, drivers, the IC, diodes 210 and 211, none of them can be causing the problem. I have checked voltages at several points and definitely found discrepancies between the two channels. But for one thing, I haven't got an oscilloscope (working on getting one but I'm a Mac user and all the ones I see and might be able to afford only work with PC), and for another, basically none of the voltages I read match up with the schematic. I'm thinking that's down to leaky elkos, so I think I'll recap the beast and see what I get. Meanwhile, your tips are very welcome!

cheers,
JP

In Topic: D150- One Channel Down!

18 November 2013 - 01:05 PM

Hi again everyone.
Soo... I'm getting around now to figuring this amp out. First I decided to make a legible diagram of the PC layout, and here is what I've got so far:

http://www.flickr.co...nd/10929222815/

PLEASE NOTE:
the linked diagram has not been checked by a real engineer, so please don't use it as a reference yet! I haven't checked it for accuracy, nor for proper PNP/ NPN orientations and the like.

For the moment, here's my question:
I'm having trouble reconciling the schematic (see above posts) with both Crown's (nearly illegible) layout diagram and the PC board in the actual amp, which I have in front of me. To be precise, it's those transistors Q102 and Q202. I'm aware that they are in a TO-92-18R package, which would make their pinout C-B-E as opposed to the usual E-B-C, right?... but still, the schematic has their bases going directly to pins 1 and 13 of the IC, which doesn't seem to be the case in reality. Also, there are two diodes on the board which seem not to appear on the schematic, as far as I can tell, in fact bridging those very two pins 1 and 13 with the collectors of those very two transistors. What gives?

THANKS AGAIN! (he screamed... sorry...)
JP

In Topic: D150- One Channel Down!

14 November 2013 - 06:54 AM

OK- working on getting this schematic into a more usable format, but for the moment here's a link to a photo of it:
http://www.flickr.co...21343/lightbox/
cheers,
JP

In Topic: D150- One Channel Down!

13 November 2013 - 07:14 AM

Ha! now here's something:
Somewhere, way back in a corner of my mind, I had a feeling I'd seen a D150 schematic in my old junk. So I opened the box of papers I'd been avoiding for aeons, and lo and behold, stuck in with the schematic for my Ampex SA-10 was a D150 schematic, not perfect but much better than the one on the Crown site. I have no idea where or when I got it, but it's on US- sized paper, and I haven't lived in the US for over 20 years, so it's at least that old. I'll take it to the copy shop today and get a hi-res scan, and post that here. I hope it helps someone out there!
All the best,
JP

In Topic: D150- One Channel Down!

10 November 2013 - 11:20 AM

Hi Alain,

First let me just say that it brightens my day to know that there are people like you who are willing to share knowledge so freely, and thank you VERY much! Sorry it took me a few days to get back; that's life around here sometimes...
I did finally find those PSU voltages at the IC; turns out the IC was not seated properly (duh). When I got the new IC to sit right, I discovered the exact same symptoms as before, so I guess that's out. Now reading 8.75 on the plus side, and -9.76 on the minus, not quite exactly within the -9.5 parameter, but pretty close.
I don't own an oscilloscope, but will pick one up as soon as I get paid. Haven't used one in many years, so I'm looking forward to it.
I checked the resistances across the outputs- no shorts. Across the plus and minus terminals of both outputs, as well as across the two plus terminals, I see a slowly growing resistance ending at around 15K ohms. I guess that's my meter charging caps in the circuit.
And yes, I confirm that there is no DC at the output terminals.

I'll keep poking around, comparing voltages, until I can get an oscilloscope on it. Till then, any more suggestions are very much appreciated!

All the best,
JP