hp 654a test oscillator - Page 3 - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd September 2008, 08:40 AM   #21
DRC is offline DRC  United Kingdom
diyAudio Member
 
DRC's Avatar
 
Join Date: Jan 2003
Location: UK (south west)
Assuming the power rails are OK :

(1) Take a look at the signal at R44, the input to the balanced amp. It should be 3v peak to peak and a perfect sinewave. Probe both ends - they should be near identical. if this is OK then the problem is in the balanced amp

(2) Check the bias point (voltage) at emitter/collector for Q13/14 Q15/16 against the figures in the schematic. Check the voltage accross R64 (should be ~11.8v and nearly dc) this provides the tail current for the Q15/16 diff-amp but is modulated by the DC balance R74/75 and C32 at higher frequencies.

(3) check the signal at the O/P R76/77. if this is very asymetric it will pull the tail current for Q15/16 out of whack - you can disable this by unsoldering Q22 base and connecting it to 0v to ease diagnosis.

PS, thx for the schematic !

dave
  Reply With Quote
Old 22nd September 2008, 08:49 AM   #22
DRC is offline DRC  United Kingdom
diyAudio Member
 
DRC's Avatar
 
Join Date: Jan 2003
Location: UK (south west)
schematic :
Attached Images
File Type: png sch.png (45.9 KB, 303 views)
  Reply With Quote
Old 22nd September 2008, 10:45 AM   #23
DRC is offline DRC  United Kingdom
diyAudio Member
 
DRC's Avatar
 
Join Date: Jan 2003
Location: UK (south west)
You can replace the tant caps with ordinary electolytic caps. this is probably better anyway as tant caps have a rather nasty failure mode. Do this before you investigate further ...

AFAIK, tant has only small size in its favor ...
  Reply With Quote
Old 8th October 2008, 02:25 AM   #24
diyAudio Member
 
deyjavont's Avatar
 
Join Date: Aug 2008
I have been having a terrible time finding a 180uF 10v (or any voltage) axial lead capacitor, aluminum or tant.

what do you guys think about using two capacitors in the place of one? I dont like that idea at all...

i dont know what else to do. i can only get the correct sprague caps in lots of like...35...and 16 dollars a piece.....eh, I could get an HP 339A and be done with it

DRC What do you mean by nasty failure mode?


(oh, does anyone have a service manual for a heathkit IM 12 harmonic distortion analyzer??)

once I get that capacitor in there...them the real diagnostics and troubleshooting begin
  Reply With Quote
Old 8th October 2008, 03:12 AM   #25
diyAudio Member
 
gain wire's Avatar
 
Join Date: Nov 2004
Location: NCR
Yopu know that C40? the 180uF? Well, where is it in the schematic because the schematic you posted is not the section you are referring to for this capacitor. I am thinking you could possibly substitute the value for maybe, 160uF or 200 uF. But I need to know the function of that cap. By the way you can check mouser, I'd rather buy there, they have more oddball components. And if that doesn't work then try Jameco, or maybe Newark.
Color test.tomato, does it work?
__________________
Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig
  Reply With Quote
Old 8th October 2008, 07:34 AM   #26
diyAudio Member
 
deyjavont's Avatar
 
Join Date: Aug 2008
yea, that schematic was posted by DRC. I bought the whole manual on pdf, great resolution too, if you would like a copy Ill just email it to you, or tell me how to post it on here.

Ill try to upload the schematic of where C40 is. I am not sure if this capacitor is what is making the output be only half a sine wave and no movement on the meter...but we will see. I think its one of the transistors in the balanced amp.

i havent tried newark yet. but everyone else has min order of at least 25 at 16 a pop. bleh.


your tomato looks great by the way
Attached Images
File Type: jpg detector.jpg (43.1 KB, 262 views)
  Reply With Quote
Old 8th October 2008, 06:09 PM   #27
diyAudio Member
 
gain wire's Avatar
 
Join Date: Nov 2004
Location: NCR
thanks for your quick reply, I might as well reply as soon as I can also. you know that 180uF (thanks for the schematic picture) well if ti's busted then the signal will not come through the average detector, which I believe is responsible for the accurate level tracking, an AGC circuit in some sorts. Can anyone else confirm? Or am I in the potatoes?
Anyway, if you take a 160uF or a 200uF (remember these components have tolerances) it will be OK. As you can guess its only function is to eliminate the DC component from the signal coming out of Q25, so as to have 0volts going to the two rectifiers. clever, if complicated arrangement for a DC tracker.
You know you might as well check what signal you have on the collector of Q25, my guess is it should be a sinewave, if it's not then, you have a problem for earlier up on the line, possibly what's feeding the average detector, the Final amplifier.check to see if
-R70, R71, are open circuit
-C31 is shorted (that would short one rail of the power supply)
Note that what I just said is for the top side, check the lower side (the PNP side of the amplifier).

I'm not trying to sound like a smart a$$ I just say what I would do. Hope it helps!
__________________
Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig
  Reply With Quote
Old 9th October 2008, 05:10 AM   #28
diyAudio Member
 
deyjavont's Avatar
 
Join Date: Aug 2008
woah gainwire! I totally forgot about tolerances! gees... a 200uF with 10% tolerance overlaps the 180uF 20% needed..
okay, I'm off to the electronics store tommorow ( I really wish someone had an all night electronics store. like..join up with 7 11 or something. haha)

I know that my power rails are in great shape. +31.0 v and -26.0 v dead on (thankful)

I wish the service manual showed what the waveform looks like when it goes through the balanced amp, because then I could verify what I am seeing on the scope is what is intended.
Once I put that cap back in (Ill do it tomorrow) Ill take some pictures of what the waveforms look like at various points in the balanced amp. hey, and gainwire, if you want the service manual for the 654A, just email me, or give me ur email. It's actually a nice pdf. great schematics

thanks again for your interest!

(the schooling I am doing right now is still at DC circuits. what a bore. haha. I guess you have to start somewhere. It will be over a year until I start doing new material for me. yawn...)
  Reply With Quote
Old 9th October 2008, 04:52 PM   #29
diyAudio Member
 
gain wire's Avatar
 
Join Date: Nov 2004
Location: NCR
yup, tolerances are one thing that can work in your favor when you can't get the right value, honestly that's the only time I think about them! Unless I'd be building a DAC r-2r ladder.
Anyway, as you say, waveforms would be helpful. I am actually surprised HP did not do this as I have a couple of HP manuals from the seventies and they do include waveforms at different testpoints. Oh well. HP kicks butt anyway!

So wait a sec here, you have two power rails, and they are not equal? That's weird. If you dont' mind I'll take kyou up on the offer... pdf please how big is the file?
Unless you've posted it on BAMA.

Oh, one thing, you'd be best off to test which way the tolerance goes, if it does go (and I am sure it will) up or down... you want the 200uF cap to go down, but check it with a multimeter, if your meter has that function. Or ask the store to check them while you're there. Jeez I always feel like I'm writing a chapter in freakin' book!

by the way I know what it feels like to be ahead of the game, the same situation happened to me in College, I knew the colour codes, part numbers, manufacturers, schematics symbols since I was like 14 yrs old. It's a good situation in which to be...

gain-wire
__________________
Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig
  Reply With Quote
Old 11th October 2008, 04:11 AM   #30
diyAudio Member
 
deyjavont's Avatar
 
Join Date: Aug 2008
I have the waveforms of what is happening at the base and collector of Q11, the first transistor in the balanced amp. I dont know what these mean (especially the one of the collector) so if you guys know, that would be great.
Attached Images
File Type: jpg dsc_3562.jpg (63.1 KB, 217 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
HP 654A oscillator dtmedin Swap Meet 0 27th February 2009 01:21 PM
Use of a Ribidum Oscillator as refrence oscillator in a DAC Mark A. Gulbrandsen Digital Line Level 18 2nd January 2009 09:57 PM
10 MHz oscillator possible to use ? Bernhard Digital Source 7 28th August 2007 09:07 PM
oscillator dsavitsk Tubes / Valves 9 15th November 2005 06:07 PM


New To Site? Need Help?

All times are GMT. The time now is 02:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2