1997 California Blonde (pre-Fender) won't power on

[Jime]

I would really like to fix this myself, but I'm a noob at electronics.

1) would this community put up with a noob asking noob questions as I try to troubleshoot this myself? If yes please skip down if you want to read more about my adventure so far.

2) if no...can anyone recommend a decent electronics technician in the Chicago or Milwaukee area? Preferably in Lake County Illinois or Kenosha County Wisconsin...but I'll drive semi-far (60-90 miles) on a strong recommendation.

Backstory
I have heard so many good things about this amp that when I saw this sad looking California Blonde in the corner of a local shop for dirt cheap ($40) "as is, does not power on"...I decided to take a chance. Thinking if I could fix it for <$100, I'd feel like Mel Fisher finding the Atocha. If I could fix it for between $100-$200...then it's still a really good deal. If I fix it for $200-$300....then I could probably just buy a new used one that already works. I figure it's worth a shot...and I'm in really no hurry to fix this thing. Some previous owner painted the top black...so I call her "Blacktop" now. I also figure as I go along this adventure I'll learn something along the way and probably meet some cool cats.

1st Troubleshooting session
During my noob troubleshooting session, I plugged Blacktop into a GFCI outlet....and the the outlet trips. I check and the power on Blacktop is off. I unplug her, make sure she is powered off, reset the GFCI, plug her back in...and the outlet flips again. I try the same thing but start with the power on....unplug her, turn the power on, reset the GFCI, plug her in, and the GFCI trips.

I scratch my head, search the web and find a bunch of schematics that I don't understand. (links below). Unscrew the head from the cabinet (that's how I know it's circa 1997), do the same stuff above and get the same results. I unplug her poke around a little bit, and nothing jumps out at me...so I take to the interwebs to see if there are sites that might help me along the way. I find this board and on the advice of user/nsubulysses, am now posting this treatise.

I think there is a short and my 1st thought is that it's in the transformer. A new transformer from Mercury Magnetics is $175...so now I'm thinkin I really need to DIY this because with a normal electronics tech troubleshooting fee + my original cost + the new transformer...I'm going to get close to my $300 marker real quick.

Other things I noticed
- the accessible fuse (from the back panel) wasn't blown
- there is a weird looking fuse soldered from the IEC to the fuse...(red arrow in one of the pics and close up in another), it looked blown but I couldn't read the writing on it, so I snipped it off and still can't read the writing on it. It was attached when the GFCI tripped on plugging Blacktop in. I didn't try to recreate the GFCI trip condition after I snipped off this fuse.

So my few noob questions right now are...
1) is there a way that noob with a DMM, wire snips, beginner solder skills, a willingness to learn, an IQ above 90, and basic logic skills can determine if the transformer is really the problem? pics of Blacktop's innards are in the link below. My thought is if I pull the transformer out of the amp, and then put power to it...I could measure it with my DMM somehow to see if it is shorting? I just don't know what to measure. I figure I can frankentape/clip the transformer to an outlet to get it power (since I don't have any super cool bench electronic testing stuff). I know there is safety to consider here, but when I've accidentally connected the circuit from a household 110 outlet with my fingers...it just scares me and gives me a shock.
1a) if the transformer is what is causing the short, what should I check next upstream? I would think that something caused the transformer to fail...it wouldn't seem like it would be a component from the board, but I have no way to know or many years of experience to know something like, "yep...it's probably this or that because of you know what".
1b) if the transformer is the initial culprit...is there a way to back into the specs of the transformer? I wonder if there are cheaper ones out there (not as good as the hand made Mercury Magnetic ones)...but also not $175. There are only 3 wires coming off the transformer.
1c) if the transformer is not what is causing the short...what should I check next?
2) how can I identify the weird looking fuse? I can't read the writing on it. Maybe from the schematics...but from what I can tell on the schematics, this extra fuse doesn't look like it's on the schematics.

so that's where I'm at right now. Thanks in advance to any "rescuers" that take pity and help me limp along this path.

Peace!
JimE


Specs that I found online...all are newer than 1997, some post Fender purchase of SWR
link to California Blonde Specs
https://support.fender.com/hc/en-us/..._Complete_.pdf

link to another set of California Specs
https://support.fender.com/hc/en-us/..._Complete_.pdf

images of Blacktop that might be relevant to this post
https://imgur.com/a/zt8ePVk

[nsubulysses]

The internal fuse is to protect the amp in case the user is careless or doesn't know any better and replaces the blown fuse with a larger one. No need to worry about that fuse if the amp blows the circuit breaker. The fuse conducts and the tripping breaker proves it.

Easy way to find out if it's the transformer ( although most of the time it's NOT the transformer) is to disconnect the two red and one black secondary windings from the circuit, leave the primary windings hooked up to the AC power from the wall and try turning on the amp again. Make sure no unsoldered secondary windings are touching anything when you turn on the amp or sparks will fly.

If it does not trip the breaker the transformer is not shorted.

There could be any number of diodes or opamps or transistors shorted in the amp that are causing the fuse to blow. Most likely culprit is output transistors I would guess.

Fixing this amp will be hard for a beginner but it could happen. MOst shops would not work on it just for the fact that it is solid state and they don't want to waste time trying to figure out what the issue is, possibly not figuring it out and wasting an hour or two.

[Leo_Gnardo]

What nsubulysses said ^^^. Plus, consider the "death cap." There very well may be one in there, it runs between chassis ground and the AC power line. If that cap is shorted or leaky, it will cause your GFCI to trip. Find it, cut it out. Then try again. If the GFCI doesn't trip now, the problem was a bad death cap. Amps get along perfectly well without them, like you would without an appendix. Not much point in replacing it.

Besided shorted output transistors, I've seen rectifier bridges go bad in these and other SWR amps.

[nevetslab]

Welcome to the Forum. As you are armed with the schematics, and I assume you've already removed the chassis from the cabinet, look at the last schematic on your first document listed. This shows the power amp circuit, and also shows the three power transformer secondary leads coming to the bridge rectifier. Unplug the two leads marked AC IN to the bridge. This will now unload the power transformer, and it can now be tested open circuit.

But, before you do anything, I would highly suggest you build yourself a Lightbulb Limiter so you can safely plug in this or any other device with a 50 or 100W incandescent lightbulb in series with the amp from the AC mains. There should be instructions on how to build this at the beginning threads of the Maintenance & Repair Forum.

Typically, the power transformer, if ok, will only draw 20-50mA (2-5W) excitation current. If instead, it causes the light bulb to glow brightly, then you DO have a bad power transformer.

What normally fails on solid state amps such as this are the output transistors. When they fail, usually C-E shorts on Q7 & Q8, and possibly Q5 & Q6, they now impose a short across the power supply, and draw HI CURRENT from the wall. If the previous owner had bypassed the AC Mains fuse, you'll have to restore that primary circuit. We're not sure if you can read a schematic enough to understand how the component symbols relate to the physical parts you're looking at, but, it does show (as you stated) only one fuse shown, and following that fuse, is a thermistor, used to lower the in-rush current when you power up the amp. It's on the same AC hot line as the fuse, ahead of the power switch. There is an X-rated cap across the line (C17, 0.01uF/250V) which rarely blows, but that is something you can check with your DMM, set for Ohms, lowest range. With the switch off, there should NOT be any resistance looking between the two AC terminals of the IEC connector (middle terminal is Chassis Ground).

I looked to see if I had any maintenance photos of the California Blond, as it's one of the many products that flow thru my shop, but I haven't taken any inside photos of it, so working from memory. There's lots of us here that have worked on these amps as well, so ask away with your questions, once you've gotten your Safe-and-sane Light Bulb Limiter box built. It saves lots of $$ in fuses, and a bright glowing bulb tells you have a short inside your amp, causing high current to flow. Those are usually something that can be found using both the ohmmeter as well as the Diode Test mode on your DMM. If it doesn't have one, it really does. Ohms mode, 2k range does the same thing....it provides a 1mA constant current behind a 2V DC source, enough to turn on semiconductors (which will read in the 0.50V to 0.70VDC in forward junctions, and open in reverse, but if a shorted transistor (Collector-Emitter junctions) is found, it will read 0.000 or near that.

Sometimes the Bridge rectifier can fail. That too can be tested with the DMM. The two symbols ~ are the AC inputs, the other two are (+) and (-). RED DMM lead on either ~ terminals, and BLK DMM on (+) will test two of the four diodes in the bridge, and reversing your DMM leads with the RED going to the (-) terminal, that tests the other two diodes in the bridge.

This should get you started.

Found this thread on servicing the California Blonde:

https://music-electronics-forum.com/...t+bulb+limiter

And this for the Light Bulb Limiter test circuit:

http://www.geofex.com/Article_Folders/SPO_Test.htm

Also, type in California Blonde into the Search Parameter box just above Advanced Search, and click on the magnifier. You'll find loads of forum threads on servicing your California Blonde.

[g1]

Not really sure how you would trip the GFCI breaker yet leave the fuses intact. So there may be a gross wiring fault even before the power gets to the transformer.
More pictures of the AC inlet area would be helpful (where the blue wire is going to from the fuse holder).

[glebert]

GFCI trip is different than an overcurrent, isn't it? I thought GFCI just looked at the current going through hot and neutral and trips if they aren't very close, which implies current going to some other path, such as the chassis.

[52 Bill]

Agree, the gfci outlet would indicate a ground fault not a shorted amp, especially one with a blown internal fuse.

Was the internal fuse actually blown or not? Did you test it with your meter?

I have a working pre-Fender California Blonde chassis in the shop. I'll have to see if it is the same as the one that you have. PM me if you're interested in a swap/trade deal.

Edit: I just looked at your photos, and it looks like there have been some mods done to the speaker wiring. If I remember correctly, the original one had hard wired speaker connections, later ones had an under sized stereo jack. It looks like yours has an added jack on the rear panel. That jack looks like it has an unsoldered connection.

[Dave H]

Not really sure how you would trip the GFCI breaker yet leave the fuses intact. So there may be a gross wiring fault even before the power gets to the transformer.

That's the first thing I'd check. Is that Mercury Magnetics PT a replacement?

A GFCI breaker is called a RCCB (Residual Current Circuit Breaker) in the UK. It trips when the difference (Residual) current between mains live and neutral is more than about 30mA which is much less than the current required to blow the amp's fuse. The internal 'fuse' could be thermistor RT1 on the schematic. If there's a current difference between live and neutral then it must be returning via ground either back through the power cord ground pin, the user or something else connected to the amp.

I'd check it by disconnecting everything from the amp (including yourself) except the IEC cable. Does it still trip the GFCI outlet? If yes then unplug the IEC from the amp so it's totally disconnected and switch on its power switch. Don't plug it in! Now measure from the amp's IEC ground pin to amp chassis. It should measure a dead short. Next measure from the amp's IEC ground pin to IEC live and neutrals in turn, both should measure open circuit. Any other reading is a fault. Avoid touching the meter probes when making the measurements or it will measure your resistance rather than open circuit.

when I've accidentally connected the circuit from a household 110 outlet with my fingers...it just scares me and gives me a shock.

That sends shivers down my spine. The mains voltage measures 250V over here. I treat it like a deadly snake and poke it with a long stick with the other hand behind my back in case it should strike unexpectedly.

[eschertron]

The mains voltage measures 250V over here. I treat it like a deadly snake and poke it with a long stick with the other hand behind my back in case it should strike unexpectedly.

Early in my career, I worked with an engineer who would treat working with high voltage wiring - even after powering it down and verifying it safe with a meter - as if it were live. His reason? Stated simply, 'Poor habits can kill you'

[Jime]

I would like to thank all of you for posting so far...I was really nervous about spilling my California Blonde guts to electronic expert strangers on the interweb.

I haven't digested everything, but I'm already overwhelmed with positive vibes on how many of you are "givers", and supportive of me (and so many others in this community)...without even knowing me.

I am going to read every post and spend some time on my makeshift bench with Blacktop on Thursday night (1/10/19 probably after 7PM CST). I will report back how it goes as I dig deeper into this as I process all the awesome comments and advice given over the past few days...I will most probably be responding to some of your posts, and will post some pics as my journey continues.

The first thing I'm going to do on Thursday night is take nevetslab's advice

But, before you do anything, I would highly suggest you build yourself a Lightbulb Limiter so you can safely plug in this or any other device with a 50 or 100W incandescent lightbulb in series with the amp from the AC mains. There should be instructions on how to build this at the beginning threads of the Maintenance & Repair Forum.

and build myself a lightbulb limiter

peace to all, for now it's off to my real job (and maybe keeping an eye on this forum in the background).

JimE

[Leo_Gnardo]

Is that Mercury Magnetics PT a replacement?

SWR amps of this period that I've worked on have Mercury OEM power transformers. Which goes to show, Mercury at one time was just another transformer company that had to bid on production contracts and supply iron at fair prices in order to be in the game, far from the huckster outfit they have become over the last 20 years.

[g1]

Mercury at one time was just another transformer company that had to bid on production contracts and supply iron at fair prices in order to be in the game, far from the huckster outfit they have become over the last 20 years.

Don't want to derail the thread, but anyone who has shook their head at the MM propaganda should have a look at the 'new' website. It looks like they may be trying to salvage their company from the snake-oilmen?