Results 1 to 19 of 19

Thread: Newbie requesting help with a dead ProCo Vintage Rat

  1. #1
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0

    Newbie requesting help with a dead ProCo Vintage Rat

    Hi,

    I've acquired a free-but-dead ~1990 ProCo Vintage Rat, the re-issue of the large format original. The prior owner said it worked last time he used it a decade ago, but it turned out to be dead when I tried it out. Here's what I've figured out so far:

    - it passes signal just fine when on bypass (switch off) whether there's a battery present or not
    - it doesn't pass signal at all when switch is on, again whether there's a battery or not
    - if you short out the battery connector (no battery, just a conductor across + to - terminal) then it does pass signal (albeit poorly) and the volume pot does attenuate the sound (obviously it doesn't distort).

    That suggests that there is a complete circuit, right?

    I can't see anything obviously blown or leaking.

    Where should I start looking? Bit worried that the op amp chip might be fried, is that something I can test?

    I have fair soldering skills and a multimeter and a desire to see this work, hoping someone can give me some pointers.

    Thanks.

    0 Not allowed! Not allowed!

  2. #2
    Supporting Member TomCarlos's Avatar
    Join Date
    Oct 2009
    Location
    Roseville, Ca.
    Posts
    705
    Thumbs Up/Down
    Received: 83/0
    Given: 192/0
    Rep Power
    10
    Is this the pedal that you have?

    https://www.electrosmash.com/proco-rat

    0 Not allowed! Not allowed!

  3. #3
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Not quite, it's this one:

    https://www.ebay.com/itm/Proco-Vinta...8AAOSwzahdDScM

    Edit: note that it looks like the original, but is actually a 1990s reissue. Identified with the word "vintage" on the serial number sticker.

    0 Not allowed! Not allowed!

  4. #4
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    3,143
    Thumbs Up/Down
    Received: 1,046/101
    Given: 143/35
    Rep Power
    12
    Quote Originally Posted by scrumper View Post
    Not quite, it's this one:

    https://www.ebay.com/itm/Proco-Vinta...8AAOSwzahdDScM

    Edit: note that it looks like the original, but is actually a 1990s reissue. Identified with the word "vintage" on the serial number sticker.
    TomCarlos link should work. Proco Vintage rat uses original circuit.

    Check the voltage for the power supply section in the link, then check for voltage on lm308 pin7.

    Then check this link for audio probe http://diy-fever.com/misc/audio-probe/
    Maybe hook an mp3 player up to proco input and then use the audio probe to see where signal stops.

    nosaj

    1 Not allowed! Not allowed!
    Last edited by nosaj; 06-25-2019 at 12:22 AM.
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  5. #5
    Supporting Member TomCarlos's Avatar
    Join Date
    Oct 2009
    Location
    Roseville, Ca.
    Posts
    705
    Thumbs Up/Down
    Received: 83/0
    Given: 192/0
    Rep Power
    10
    Scrumper:

    Take a look and see if what you have matches (or comes dawg on close) to the schematic from the Original Rat. Check the Power Supply Voltages and voltages on the IC. Give us the pins and voltage that you measure.

    Tom

    0 Not allowed! Not allowed!

  6. #6
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    3,143
    Thumbs Up/Down
    Received: 1,046/101
    Given: 143/35
    Rep Power
    12
    Quote Originally Posted by TomCarlos View Post
    Scrumper:

    Take a look and see if what you have matches (or comes dawg on close) to the schematic from the Original Rat. Check the Power Supply Voltages and voltages on the IC. Give us the pins and voltage that you measure.

    Tom
    Tom i used this for my determination of the circuit.https://www.diystompboxes.com/pedals...t_versions.htm
    nosaj

    1 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  7. #7
    Supporting Member TomCarlos's Avatar
    Join Date
    Oct 2009
    Location
    Roseville, Ca.
    Posts
    705
    Thumbs Up/Down
    Received: 83/0
    Given: 192/0
    Rep Power
    10
    Nosaj... good find on that document. If nothing else, Scrumper can check to see if the Power Supply looks similar to one of the circuits and the IC with surrounding components.

    0 Not allowed! Not allowed!

  8. #8
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    11,717
    Thumbs Up/Down
    Received: 1,848/22
    Given: 1,446/35
    Rep Power
    26
    "First fix DC, then Audio"

    Meaning: first measure and post voltage on all IC pins.
    Then if normal start checking signal along the path from input to output to see where it gets lost.

    2 Not allowed! Not allowed!
    Juan Manuel Fahey

  9. #9
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Thanks all for excellent advice. Will be tackling this at the weekend - honestly wasn't expecting such a quick response.

    I'll report back then with voltages and other findings.

    1 Not allowed! Not allowed!

  10. #10
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Ok I had a look. It's not an LM308 Rat, this has an DPOP07 op amp, making it a bit newer. The circuit is different to those in the links above. It says "MULTI RAT" on it. Some capacitors are not included.

    Voltage across the chip (pin 4-7 according to this: https://www.analog.com/media/en/tech...heets/OP07.pdf) is 0.48V using a 9V battery that reads 8.5V.
    Voltage between battery negative and pin 7 is 8.3V - don't understand why that's the case.

    I managed to get hold of an old oscilloscope, fed the pedal a sawtooth wave from a synth, and found that when the footswitch is not in bypass the chip is outputting on pin 6 a very low (millivolt) signal which is affected by the Filter and Distortion knobs. This signal appears to be a very noisy copy of the input signal on pin 3. There's also a copy of the input signal on pin 4 which is supposed to be ground. This goes away when the footswitch is in bypass.

    This suggests to me the chip is damaged: am I right that the output shouldn't be a an orders-of-magnitude lower copy of the input, especially where the chip is intended to be overloaded to color the signal like here?
    (The other thing maybe is there's maybe something wrong with the ground, a short somewhere or a broken switch? Why am I seeing the input signal on the chip's ground pin otherwise? I guess could be another symptom of the chip failure).

    So it's a bit weird. I'm trying to trace out the circuit and figure what's what but it's a bit difficult with the circuit on one side and the components on the other - and the component side has space and labels for many things which aren't there. When I was 16 I studied and enjoyed electronics at school but that was 30 odd years ago and I've not thought about it since, so please bear with me while I scrape off decades of rust!

    0 Not allowed! Not allowed!

  11. #11
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    3,143
    Thumbs Up/Down
    Received: 1,046/101
    Given: 143/35
    Rep Power
    12
    Quote Originally Posted by scrumper View Post
    Hi,

    I've acquired a free-but-dead ~1990 ProCo Vintage Rat, the re-issue of the large format original. The prior owner said it worked last time he used it a decade ago, but it turned out to be dead when I tried it out. Here's what I've figured out so far:

    - it passes signal just fine when on bypass (switch off) whether there's a battery present or not
    - it doesn't pass signal at all when switch is on, again whether there's a battery or not
    - if you short out the battery connector (no battery, just a conductor across + to - terminal) then it does pass signal (albeit poorly) and the volume pot does attenuate the sound (obviously it doesn't distort).

    That suggests that there is a complete circuit, right?

    I can't see anything obviously blown or leaking.

    Where should I start looking? Bit worried that the op amp chip might be fried, is that something I can test?

    I have fair soldering skills and a multimeter and a desire to see this work, hoping someone can give me some pointers.

    Thanks.
    Quote Originally Posted by scrumper View Post
    Ok I had a look. It's not an LM308 Rat, this has an DPOP07 op amp, making it a bit newer. The circuit is different to those in the links above. It says "MULTI RAT" on it. Some capacitors are not included.

    Voltage across the chip (pin 4-7 according to this: https://www.analog.com/media/en/tech...heets/OP07.pdf) is 0.48V using a 9V battery that reads 8.5V.
    Voltage between battery negative and pin 7 is 8.3V - don't understand why that's the case.

    I managed to get hold of an old oscilloscope, fed the pedal a sawtooth wave from a synth, and found that when the footswitch is not in bypass the chip is outputting on pin 6 a very low (millivolt) signal which is affected by the Filter and Distortion knobs. This signal appears to be a very noisy copy of the input signal on pin 3. There's also a copy of the input signal on pin 4 which is supposed to be ground. This goes away when the footswitch is in bypass.

    This suggests to me the chip is damaged: am I right that the output shouldn't be a an orders-of-magnitude lower copy of the input, especially where the chip is intended to be overloaded to color the signal like here?
    (The other thing maybe is there's maybe something wrong with the ground, a short somewhere or a broken switch? Why am I seeing the input signal on the chip's ground pin otherwise? I guess could be another symptom of the chip failure).

    So it's a bit weird. I'm trying to trace out the circuit and figure what's what but it's a bit difficult with the circuit on one side and the components on the other - and the component side has space and labels for many things which aren't there. When I was 16 I studied and enjoyed electronics at school but that was 30 odd years ago and I've not thought about it since, so please bear with me while I scrape off decades of rust!
    Looks like your on you own, would've been saved some time instead of telling everyone it was a 90s Vintage Rat, when in fact it's printed with Multi Rat.

    Good luck this is all that's out there.
    https://www.youtube.com/watch?v=ETM8Rx2xKMM
    nosaj

    0 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  12. #12
    Supporting Member TomCarlos's Avatar
    Join Date
    Oct 2009
    Location
    Roseville, Ca.
    Posts
    705
    Thumbs Up/Down
    Received: 83/0
    Given: 192/0
    Rep Power
    10
    From the datasheet

    Pin 1 VOS trim
    Pin 2 (-) input
    Pin 3 (+) input
    Pin 4 V-
    Pin 5 No connection
    Pin 6 Output
    Pin 7 V+
    Pin 8 VOS trim

    You mentioned reading 8.3 volts from pin 7 to the battery negative terminal. But if you move the black lead to pin 4 you get nothing? Follow the trace from Pin 4 back to the negative terminal. Make sure you do not have bad solder connections anywhere along that trace. Maybe you can solder in a jumper wire from the negative terminal to a point near the IC? See if that does anything?

    Let me add, check that switch once again. Maybe it needs to be cleaned or replaced.

    2 Not allowed! Not allowed!

  13. #13
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Quote Originally Posted by TomCarlos View Post
    You mentioned reading 8.3 volts from pin 7 to the battery negative terminal. But if you move the black lead to pin 4 you get nothing?
    Not nothing - I get 0.5V across pins 4->7. It should be ~9V, if I'm reading the schematic correctly. I will check that path back to the terminal as you suggested.

    Could be a fault in the switch screwing up the ground - I'll check that too.

    (And nosaj - apologies for wasted time. I didn't see it was a "Multi Rat" until I had the thing in pieces and flipped the board over this weekend. Everything else including the serial number makes this out to be a ProCo Vintage Rat. My guess is this someone's kit-built thing, like your video, stuffed in a Vintage Rat case. It doesn't have that selector rotary like in the video.)

    0 Not allowed! Not allowed!

  14. #14
    Senior Member
    Join Date
    May 2006
    Location
    Cheshire, UK
    Posts
    2,198
    Thumbs Up/Down
    Received: 503/4
    Given: 277/0
    Rep Power
    16
    Quote Originally Posted by scrumper View Post
    Voltage across the chip (pin 4-7 according to this: https://www.analog.com/media/en/tech...heets/OP07.pdf) is 0.48V using a 9V battery that reads 8.5V.
    Voltage between battery negative and pin 7 is 8.3V - don't understand why that's the case.
    It's most likely because pin 4 is open circuit from ground/battery negative. With the battery disconnected check for continuity between battery clip -ve and pin 4. If it isn't a very low resistance find out where the open circuit is and correct it then do as Juan said and check the DC voltages on the op amp pins wrt battery -ve. They should read 4.5V on pins 2,3 and 6. 9V on pin 7 and 0V on pin 4.

    1 Not allowed! Not allowed!

  15. #15
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    6,175
    Thumbs Up/Down
    Received: 1,101/1
    Given: 875/1
    Rep Power
    16
    Normal pedal architecture has the ground path completed when a plug is inserted into the input jack. You do have a plug there for testing?

    5 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  16. #16
    Senior Member
    Join Date
    May 2006
    Location
    Cheshire, UK
    Posts
    2,198
    Thumbs Up/Down
    Received: 503/4
    Given: 277/0
    Rep Power
    16
    Quote Originally Posted by The Dude View Post
    Normal pedal architecture has the ground path completed when a plug is inserted into the input jack. You do have a plug there for testing?
    Yes, good point!

    0 Not allowed! Not allowed!

  17. #17
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Quote Originally Posted by Dave H View Post
    It’s most likely because pin 4 is open circuit from ground/battery negative. With the battery disconnected check for continuity between battery clip -ve and pin 4. If it isn’t a very low resistance find out where the open circuit is and correct it then do as Juan said and check the DC voltages on the op amp pins wrt battery -ve. They should read 4.5V on pins 2,3 and 6. 9V on pin 7 and 0V on pin 4.
    This was instructive - there is an open circuit there. Didn't get far figuring out exactly where last night - maybe one of the capacitors just up from pin 4 is fried but not sure yet.

    This is great though - I have something to go on now. Thank

    The Dude: I did have a plug in the input jack, but worth pointing out!

    3 Not allowed! Not allowed!

  18. #18
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    6,175
    Thumbs Up/Down
    Received: 1,101/1
    Given: 875/1
    Rep Power
    16
    Maybe this will help- schematic with notes/changes for the various Rat pedals.

    https://music-electronics-forum.com/...6&d=1387061571

    2 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  19. #19
    Junior Member
    Join Date
    Jun 2019
    Posts
    7
    Thumbs Up/Down
    Received: 4/0
    Given: 4/0
    Rep Power
    0
    Thanks The Dude - I found that very helpful indeed. That covers my circuit.

    Managed to get distorted but quite crap sounding audio out of it after connecting pin 4 direct to a known-good ground point. Investigating now where the open is between 4 and the point its connected to in the actual circuit, which is the DPDT switch. I have a feeling the switch is bad so the chip might not be the only thing that isn't grounded.

    I'm tempted at this point to make a clone of an LM308 rat and use my existing pots, jacks, and housing. Whatever it is that's broken will be fiddly.

    Thanks all for the help.

    0 Not allowed! Not allowed!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Requesting for Schematics
    By wilby.hagley in forum Schematic Requests
    Replies: 1
    Last Post: 02-28-2016, 10:36 PM
  2. Newbie Question: Death Cap in Vintage Fender 3 prong corded amp
    By keithb7 in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 01-02-2016, 01:57 AM
  3. (relative) Newbie Q: Amp is dead / no symptoms. Thoughts?
    By Musicalbox23 in forum Guitar Amps
    Replies: 7
    Last Post: 04-14-2010, 01:42 AM
  4. LM 308H type in a proco Rat.
    By pbdog in forum Guitar Effects
    Replies: 3
    Last Post: 10-09-2007, 02:26 PM
  5. HELP with a Vintage Amp that's dead...
    By strangedogs in forum Maintenance, Troubleshooting & Repair
    Replies: 12
    Last Post: 06-23-2007, 06:51 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •