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Can I fix this old Pioneer SR303 Reverb myself?

mikehende

Dec 22, 2006
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I might be able to get one locally for $100 which is in mint condition, that would be less than the repair cost. I am thinking that would be the better way to go, should I run into issues with it in the future then most likely I can use mine for parts for repair option assuming it's not the same issue.
 

johnnyz

Feb 11, 2022
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Can you pick up where you left off and help me out with my Pioneer SR-303?

I have a Pioneer SR-303 that comes on, has power but I got no output and no display on the screen and no output. I have the service manual, and I know how to read it but still learning. I know how to use my multimeter and I know what transistors, caps, diodes are. I can order parts from mouser and change them out. What I can’t do is figure where to start and how to troubleshoot this to find out what’s wrong.
 
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johnnyz

Feb 11, 2022
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TP1 reads 0.679v with reverb time nob set to 0 and 3.466v at 100%
TP2 reads 20.2mv with reverb time nob set to 0 and 20.7mv at 100%
TP3 reads 2.4mv with Depth nob set to 0 and and is reading the input signal and goes over a 100mv when turning up the nob
TP4 reads 171.3mv
TP5 reads nothing .5mv
I am getting 23.96v off the main power transformer
 

kellys_eye

Jun 25, 2010
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TP4 and TP5 should read approx +/-15V (with respect to ground) - since they show 0V (as good as) the first suspect would be R1 (open circuit) however this itself would only 'blow' if there was a fault further into the circuit.

Are you sure you're reading DC voltages at the TPs' and not left the meter on AC after reading the transformer?
 

johnnyz

Feb 11, 2022
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TP4 and TP5 should read approx +/-15V (with respect to ground) - since they show 0V (as good as) the first suspect would be R1 (open circuit) however this itself would only 'blow' if there was a fault further into the circuit.

Are you sure you're reading DC voltages at the TPs' and not left the meter on AC after reading the transformer?
Thank you for getting back to me.

UPDATE - OK ya I think the meter was on AC. DC now and reading:

TP4 -0.191v On that resistor right before that it says it should have 28v and it only has 9v so something before that and then 0.4V, tracing back. I don’t know I am new to this electronics repair stuff :(. See picture and if you could let me know where to check next, how to trace this back?

TP5 -15.38v
 

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kellys_eye

Jun 25, 2010
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Check D13. If that checks out ok then snip the wire link (second left of C36) and see if TP4 voltage rises.

Note - above TP4 is C37. To the left is C36 followed by two wire links. Snip the second link.

This is the (dodgy) 15V supply to the rest of the device and if there is a fault 'further in' then the 15V could be being dragged down. Cutting that link removes any 'drag' on the 15V rail and if the 15V rail goes back up to anywhere near what it should be then the fault is further in on the equipment.

I have an unwritten rule though - if there's a zener diode in the circuit the zener diode is the fault.....:)

D13 is the 'zener' and I reckon it's gone short.
 

johnnyz

Feb 11, 2022
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Sorry just started to learn how to do this 1 week ago. How would you like me to check D13? I have a Fluke 179.

Diode Test mode its 0.722 in circuit power off.
 

kellys_eye

Jun 25, 2010
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Sorry just started to learn how to do this 1 week ago.

....and you've splashed out on a Fluke 179!!!! Wish I had the moolah! Anyways......

Turn the dial to the yellow 'diode' position then press the yellow button. Place the probe leads across the diode. One way will (should) read 'infinite' and the other should read 0.6 to 0.8V. If it's zero both ways then the diode is shorted (can be checked by pressing the yellow button gain to revert to the continuity mode and you'll hear it 'beep' with the leads connected either way around on the diode.
 

johnnyz

Feb 11, 2022
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....and you've splashed out on a Fluke 179!!!! Wish I had the moolah! Anyways......

Turn the dial to the yellow 'diode' position then press the yellow button. Place the probe leads across the diode. One way will (should) read 'infinite' and the other should read 0.6 to 0.8V. If it's zero both ways then the diode is shorted (can be checked by pressing the yellow button gain to revert to the continuity mode and you'll hear it 'beep' with the leads connected either way around on the diode.

Diode Test mode one way is 2.179 and the other 0.722 in circuit power off.
continuity mode on way is OL and the other 732
 
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johnnyz

Feb 11, 2022
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PS.I have had a WaveTek for most of my life but when I decided it was time to start learning how to do this I found a like new 179 on ebay for $150 :)

Next is a signal generator and oscilloscope. I really need to learn this. I can do just about anything. I am a fast learner and it really bothers me when I dont know how to do something.
 
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johnnyz

Feb 11, 2022
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Yes that is the one I did, not C36

And now with closer inspection it looks like it got hot in that area. And is that glue or did these CAPs leak? I think its glue.

Ok that CAP is defiantly bad. So would somthing take that out or is it ok just to order a couple of thoes and put them in?
 

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kellys_eye

Jun 25, 2010
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The heat comes from the two 100 ohm resistors R118/R119 which is 'normal' - however with the lack of input voltage (you show 9.4V where there should be 28V) you could cut one end of R118 to see if the voltage (where you show 10.48V) rises to 30-ish volts.

If the voltage doesn't rise then test (replace) C41, test D11 and then test R1 (off board).

Capacitors ARE prone to failure over time so replacement of all the electrolytics in the power supply section wouldn't be a bad thing (preventative if anything else) and MAY be the cause of the current issues of lack of voltage. The 'gunge' is indeed glue, commonly used to prevent physical movement.
 

johnnyz

Feb 11, 2022
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Thanks for the info.
So I just wanted to share this as things changed when I pulled out that bad Capasitor. Here are the new readings with out the cap in. let me know if you still want me to cut one end of R118 to see if the voltage (where you show 10.48V) rises to 30-ish volts. or if it may just be this bad cap? Also should I replace these to caps to 50V when I order?

RFS-50V471MJ8#5 Elna | Mouser
 

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kellys_eye

Jun 25, 2010
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Using higher voltage caps is ok so long as they fit physically - you obviously can't use lower rated!

The voltages are correct with that cap out so it points to it having dried out/gone short. If you had an ESR meter you could check the other caps but replacing them all would be easier and just as quick.

If you were 'serious' about the equipment and wanted to ensure longevity then replace ALL the electro capacitors throughout - especially those used to filter supply lines. As mentioned before, dud capacitors are VERY common in older equipment and restorers often replace them as a matter of course.
 

johnnyz

Feb 11, 2022
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Also like I have said I am just getting started on this. I see these "breadboards" used a lot for testing etc... can you tell me what is good to get? I don’t have anything so I would need a kit with the pins/wire/leads, whatever.
 

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kellys_eye

Jun 25, 2010
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Breadboards are ok for jury-rigging parts to test and even some small circuit testing and that one seems as good as any you can get.

You will find that you start building up a selection of parts and equipment so consider setting some space apart for it all. You might end up like me and have three sheds of 'crap' and a workshop you can't climb in/out of over the 'stuff I want to build/fix'. Life has this nasty habit of getting in the way of fun.
 

johnnyz

Feb 11, 2022
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Breadboards are ok for jury-rigging parts to test and even some small circuit testing and that one seems as good as any you can get.

You will find that you start building up a selection of parts and equipment so consider setting some space apart for it all. You might end up like me and have three sheds of 'crap' and a workshop you can't climb in/out of over the 'stuff I want to build/fix'. Life has this nasty habit of getting in the way of fun.
Thanks. Yes I get what your saying. Story of my life. I have A-D-D or somthing. I learn how to do somthing and move on to the next thing. Lucly I am very organized. But yes I have only been doing this a couple weeks and my bench is full and I am still ordering stuff daily.
 
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