I've got the grainy scan of a third generation photocopy of the original service manual that Harman/Crown put online. It has part locations superimposed over a grainy picture of the board artwork but not a proper schematic.
I've got the much better scan of the Series II service manual with its decent schematics, but my DC-300A is not a Series II.
Since google doesn't really do real verbatim searches anymore, it just keeps leading me to the same PDFs in different places.
I've read through the threads here about this amp, and i think I've seen references to the existence of a good clean schematic file somewhere?
Anyone?
I've got the much better scan of the Series II service manual with its decent schematics, but my DC-300A is not a Series II.
Since google doesn't really do real verbatim searches anymore, it just keeps leading me to the same PDFs in different places.
I've read through the threads here about this amp, and i think I've seen references to the existence of a good clean schematic file somewhere?
Anyone?
The manual pdf on the mfr web site looks as good as the original manual.
Bear in mind how long ago it was published. The pcb diagrams look like
photocopies of boards, scanned as an image.
Here's another source for a schematic.
http://www.radiomuseum.org/r/intern_rec_dc_300a.html
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Hifi Engine had a pretty good copy of the manual...I'm not sure how it compares to what you've already found.
https://www.hifiengine.com/manual_library/crown/dc-300.shtml
you may have to login to be able to download it.
https://www.hifiengine.com/manual_library/crown/dc-300.shtml
you may have to login to be able to download it.
I believe this might be a better copy of the schematics here: Crown DC300 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
The one from eserviceinfo is a bit cleaner and contains most of the schematic (a bit is lost between pages there).
Based on the thumbnails at radiomuseum they have the same version as eserviceinfo.
I guess i can extract the images and see if any whole components or information are missing when i fit them together in an image editing tool
hifiengine has the same file harman is distributing.
Thanks.
Oh wait, that is the whole schematic in the eserviceinfo version. I just have to overlap the images just right.
I'll post up whatever i manage.
I'll post up whatever i manage.
Go right to Crown under their discontinued amps, all of their service lit is there for download. All of the DC300s are there. The IIs got rid of that dreaded Ua739/749 opamp for starters.
Craig
Craig
The file that Crown (now Harman (now Samsung)) supplies lacks the schematic. See comments above.
The II adds the clipping/DC detection, but through serial number 81323 it still has the UA739.
S/N 81324-up switched to the LF357.
Since the LF357 is internally compensated, maybe the late version is easier to upgrade to a modern part.
I'm not an EE, but my reading of the original schematic suggests that the "lag" or compensation networks on the UA739 are only connected to power and ground aside from the chip itself, so it's possible that i could make an adapter that would let me use a modern dual opamp, and just not connect those pins, but I imagine that other changes to the preamp & drive circuit may need to be altered to retain stability.
A few websites sell little modules to replace some DIP-14 opamps (including the UA739) with an ne5532, but I'm not paying $35 for a $1 chip on a board.
I hadn't been to the Crwon website in a while, it has changed quite a bit. I'm glad I downloaded that stuff years ago. I have DC300A on the back burner and it's been repaired so many times before I got it I just stripped it down to the bare bones in order just to start over. Since just about every semiconductor is obsolete and hard to find I've thought about getting a White Oak Phase Linear PCB and installing that. The output stage is almost exactly the same. Might to make a few resistor changes in the front end to compensate for the lower PS voltages.
Craig
Craig
I bought mine for $30 from a snaggle-toothed trailer park dweller who was under the impression that since it doesn't pop fuses it's working.
Has the original white can capacitors sticking out the back, one of which has some good dents in it.
Has 16 matching Motorola 3990 output transistors. All the big can transistors have the same thing scribbled on them with red sharpie but I'm not sure what it's supposed to be.
Not a lot of wear on the screws and the output device covers were not missing.
I saw the thread where a guy etched new boards for some minor component updates and rebuilt his DC300A-II from the ground up. Pretty impressive.
I'm toying with the idea of updating it to the late DC300A-II and using a decent modern or at least semi-modern part for the opamps. I am plenty comfortable etching and drilling single-sided boards.
If all or even most of my output parts are still good i don't see a reason to spend $100 on all-new OnSemi TO-3 parts like that one guy.
Right now my basic plan is to start by replacing the 100uf cap and 10v zener that seem to always fail, and then go through the diagnostics in the manual to see if it is working properly.
I am really itching to replace those big can caps, both because of the age and because of the dents. I need to get on the phone with Apex Jr and see if he has a pair on the shelf that look like likely candidates. Dunno that 47,000uf like that one guy used is necessary, but i will probably go up from the original 15,200uf.
Some time soon I'll probably build a spreadsheet with the parts - Crown seems to have retained component numbers throughout the 3 versions of the amp. Little things, like C107/207 don't exist in the late DC300A-II.
Has the original white can capacitors sticking out the back, one of which has some good dents in it.
Has 16 matching Motorola 3990 output transistors. All the big can transistors have the same thing scribbled on them with red sharpie but I'm not sure what it's supposed to be.
Not a lot of wear on the screws and the output device covers were not missing.
I saw the thread where a guy etched new boards for some minor component updates and rebuilt his DC300A-II from the ground up. Pretty impressive.
I'm toying with the idea of updating it to the late DC300A-II and using a decent modern or at least semi-modern part for the opamps. I am plenty comfortable etching and drilling single-sided boards.
If all or even most of my output parts are still good i don't see a reason to spend $100 on all-new OnSemi TO-3 parts like that one guy.
Right now my basic plan is to start by replacing the 100uf cap and 10v zener that seem to always fail, and then go through the diagnostics in the manual to see if it is working properly.
I am really itching to replace those big can caps, both because of the age and because of the dents. I need to get on the phone with Apex Jr and see if he has a pair on the shelf that look like likely candidates. Dunno that 47,000uf like that one guy used is necessary, but i will probably go up from the original 15,200uf.
Some time soon I'll probably build a spreadsheet with the parts - Crown seems to have retained component numbers throughout the 3 versions of the amp. Little things, like C107/207 don't exist in the late DC300A-II.
If that's the case, up the 100uF to a higher voltage rating, and to 105C if possible.
Also up the Zener to the next higher power rating.
Mouser sells a Kemet axial 200v 100uf cap that is rated for 27,000 hours at 105c. I had to double check the datasheet to make sure that wasn't a typo. That's what I'll be using.
The original zener was rated 500mw, a 1w part shouldn't be a big deal to source. Edit: but Mouser doesn't stock any axial zeners rated higher than 500mw?!
I read a whole bunch of DC300A threads, and those two parts are the biggest culprits of failure.
Mouser has 1N47xx series, those are 1W.
I know I've had few bad Ua739s in the few Crowns I've worked on, can't get the DC offset to adjust correctly.
Craig
I know I've had few bad Ua739s in the few Crowns I've worked on, can't get the DC offset to adjust correctly.
Craig
I have one DC-300 i bought off a grad student at NYU for peanuts -- i think that prior tenant of their apartment had abandoned it there. Also got an IC150 preamp which I have spiffed up.
Sold all the semi's, and driver board, replaced the Crown circuitry with an LM4702 (now obsoleted by TI).
They really were built on the cheap.
IMO, it's a good idea to pull all the outputs and check the breakdown voltage. I was surprised at how little safety factor they can have. That, and check the matching. It's done by Vbe, not by hfe.
Yeah, turns out that the mouser search engine doesn't know that "axial" and "through hole" are the same thing. Found it.
Never used the "axial" search for Zeners, always thru-hole. I know there were "radial" Zeners, TO-92 case, at one time as my GAS SON uses them. I don't think I've ever looked for them though.
Craig
Craig
Is that a tantalum capacitor? If so, I'd still go for an electrolytic type.
Here's a 1W Zener. Don't go any higher in power rating than 1W, though.
Make sure that the new part's leads will fit the pcb holes.
1N4740A ON Semiconductor / Fairchild | Mouser
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From the datasheet:
PEG124RB2100QL1 KEMET | Mouser
Huh, maximum 10 whole ohms ESR at 100hz. That gives me a little pause. (Edit: on second thought, no it doesn't. All the high temp high volt 10uf caps have somewhat high ESR)
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