JC 120 wont turn on help please

[ifeuerman]

A few days ago i had been playing my jc 120 which i believe is from '79 with no problems, then yesterday i went to play and the light would not turn on and no sound was being made. Is it possible the culprit is the fuse or possibly the power cord has become unattached somehow? I really would like to continue to use this amp and my local amp shop charges a hell of a lot to even assess the cause of such an ailment but if anyone could help me the assistance would be greatly appreciated. If the reason is the cord how would I go about accessing it in that it is attached with in the amp and I am by no means skilled in amp repair.

Also on my particular amp the fuse seems incredibly hard to get at in that i keep turning it but it wont come out if there is an easy way to get the fuse out id love to know.

Thanks for the help

[Enzo]

Hi ifeuerman, welcome to the forum. A lot of people will be willing to help.

May I suggest, just start a new thread for your amp, or pick ONE thread to pursue it. Posting the same message five times in the same board is considered bad form in a forum such as this one.

[Alex R]

...my local amp shop charges a hell of a lot to even assess the cause of such an ailment

The reason for that may be that once a repairman has 'assessed the cause' of a problematic amp - ie knows everything that is wrong with it - he has often 90% fixed it. The customer demand for estimates, whilst understandable, does tend to drive up repair prices.

[ifeuerman]

Thanks alex i think your right im just going to have to bring it in and let a professional handle it i just dont wanna end up paying $65 for the guy to determine that its some simple fix that i could have done my self

[Alex R]

Fuse failures usually have deeper causes. Yes it could be the cord though it's not that common. If you're not confident taking the chassis out then I think you do need the repairman. Btw it is worth bearing in mind that many of those who offer advice on this forum also make their living or part of it from repairs.

[km6xz]

Do you have any test instruments? A digital multimeter would be the minimum but luckily they can be purchased for very little. $20 for example, that are 5 times more accurate than is required for amp repair.
The first step would be to measure the resistance of the fuse, some are ceramic so you can't see if their are blown or not. It is blow, showing very high or infinite resistance on the meter, it might be better to let the tech do it. It is a relatively simply amp to repair and has proven to be quite reliable. If the fuse is good, there is a chance it is just the AC cord, power switch or a bad connection. With some simple checks with the meter we can help you determine if it is simple or complex and how much a competent shop ought to charge for a repair.
Here is a circuit diagram but bear in mind that the same model number, JC-120 was revised a number of time, sometimes changing the circuit quite a bit, particularly its chorus circuit. They all sounded alike but newer versions were a little quieter.
http://www.freeinfosociety.com/elect...C120-JC160.pdf

Estimates are essentially paying for the most critical aspect of a repair, the diagnosis. A good diagnosis saves a great deal of time and money, everything afterward is just mechanical labor. The skill is in diagnosis. If the shop did provide a complete estimate for a reasonable charge you could fix it yourself based on an accurate diagnosis. You can tell quickly if it is a hack who is guessing by the number of unrelated parts replaced and charged for. Some cases, like a damaged power amplifier can generate enough current and heat to damage a number of parts quickly but most circuits fail for single component failures.
Many shops have eliminated estimates, which are time consuming to do right, and have gone to fixed price flat rate based on model, power, number of channels or other criteria. Those with simple repairs are subsidizing the more complex repairs, and paying too much. Those with complex expensive repairs, if charged hourly, are getting a good deal, below what they would pay a shop doing work by time. If you knew it was easy, take it to a shop that charges for work actually performed, and if a complex repair(a JC120 is never a complex repair), take it to a shop that has a flat rate.

[Twist]

In response to "Alex R" I too agree. Every time I've offered free advice to someone on here on how to fix their amp I feel like I may have taken away a repair from the local amp tech in that town. It's probably happened to me. There's nothing worse than receiving an amp for repair that the customer has made an attempt to repair themselves. It generally cost them more in the long run.

[Alex R]

Oh I don't mind sharing information, that's what the forum's about. I just wanted to point out that no-one should be surprised if estimates aren't cheap, as once you know what's wrong the hard skilled work is done.

I find my customers are happy to work on trust on the whole. I guarantee not to charge more than the amp is worth, and to let them know if things are getting expensive, and that seems to make them happy. Maybe I have a good demographic, maybe I'm just cheap, who knows...

But yes, sorting out a badly repaired amp can create really tricky jobs, especially without a schematic.

I'd agree that JC120s are usually ok to fix, but by no means always, unless I am way stupider than km6xz (always a possibility), especially if the delay preamp goes awry. They went through a lot of versions, schematics aren't always available, plenty of obsolete ICs and quite a complex time-delay circuit to figure out...

[jrfrond]

The whole issue of estimates and such is another topic entirely for all of us professional managers/owners. There is no perfect way around it. We charge for estimates up-front, and the fee sits at two levels (one or two hours labor), depending on what the gear is and the complexity. It is non-refundable and if the repair is performed, it is deducted from the final bill. Since I write up all estimates, I've learned how to over-estimate, always giving the customers a worst case scenario, as well as making them aware of NYS Fair Trade Laws, which dictate that +/- 20% deviation from the quoted estimate is legal, plus making them sign off on the estimate. However, the only way you can implement all of this is to have a stellar reputation for being honest, which we are, sometimes to a fault.

As Stan pointed out, the diagnosis is the most crucial part of the estimate. The rest is mostly mechanics. One of my favorite repair anecdotes goes like this:

A man calls a plumber to his house for a leaky faucet. The plumber comes, stays a half-hour to put in a new washer and hands the guy a $50 bill. The customer complained "Hey, all you did was put a tiny little washer in and charged me fifty bucks!" The plumber said "The washer cost 5 cents. The remaining $49.95 was for knowing where to put it".

Oh, the original question: a JC120 doesn't turn on? Worst-case scenario: bad power transformer. Likely scenario: bad power cable (easy), or open fuse (could be easy, but might be more complex if it was caused by a short).

See what I mean? Oh yes, no charge.....

[Steve Conner]

Oh, I thought that one went:

Customer: "$49.95 for a half hour's work? I don't make that much as a lawyer!"
Plumber: "Neither did I"

[jrfrond]

Oh, I thought that one went:

Customer: "$49.95 for a half hour's work? I don't make that much as a lawyer!"
Plumber: "Neither did I"