channel loss and amp chips!!!

[bibox]

For hi-fi applications, I have heard that silver blend solder gives superior results. However, for lo-fi applications such as boomboxes,

Silver solder is probably not worth it as you surmise. It is also more expensive and can be hard to find. In the US, Kester 44 is the old stand-by for both repair shops and hobbyists. I can't count the number of projects I've used it on. Everything from tube amp builds to car audio circuit board repairs. It is great!. A 1 lb. spool in 0.031" size will last you a decade.

What you do not want is RoHS compliant solder. Eventually that will be all you can buy but for now you don't have to. RoHS solder is a b*tch to use. You need a hotter iron and more of it to keep from getting a cold solder. It is a real PIA. RoHS stands for "Removal of Hazardous Substances" i.e, lead. Lead is replaced with another element and it does not flow like lead.

 

[saxonman]

that RoHS is the stuff I've got which is lead free!! I'll use my old reel which is about 20yrs old!! I've now stripped it right down and have gave it a hot bath!!!!! soo all being well, and the chip works it will be fully operational and clean!!

 

[Superduper]

Oh. I should say that it's not unusual to find counterfeit "original" semiconductors out there. Most anything found in China is counterfeit. So if the new amp chip doesn't work right, just keep in mind that the issue can still be the amp chip. I have experienced that on several occassions, especially with fake HA1392 amps.

 

[saxonman]

this has hitachi on it like my one!!! it was on ebay BIN so hopefully it'll be good I did see lots for $5 but just kept to private uk sellers!!

 

[Superduper]

this has hitachi on it like my one!!! it was on ebay BIN so hopefully it'll be good I did see lots for $5 but just kept to private uk sellers!!

I would say especially eBay stuff, could be counterfeit but sometimes, there is no choice. The counterfeit stuff are mostly not up to snuff.

As for the hitachi name, trust me when I say that if they go to the trouble of manufacturing a fake chip, putting the hitachi name on it is the easiest of the counterfeiting process.

 

[saxonman]

yer see ya point superdude!!

 

[saxonman]

right changed the chip now and it's the same but alot louder and clearer!! there is a faint volume on the the dead channel !!! what do ya reckon??

 

[Superduper]

What is the part number of the amp module?

 

[saxonman]

ha1392 i'm sure this new one is ok as it's got the same problem!!! is there anything else which could be between the amp and connection!!

 

[Superduper]

OK. This is how I troubleshoot such problems. Pins 2 and 5 are the inputs to the amp. One is left and one is right. Unless you have dual amp chips, in which case, both are inputs to the same channel, operated in bridged mode. The pins are usually enumerated from left to right, looking at the chip with pins down and silkscreening facing you.

I inject a 1khz audio signal (line-in) or you could use cassette tape recorded with a 1khz audio signal, or RF generator etc. I then trace backwards from the amp towards the preamp using a signal tracer but you could try using a millivoltmeter. Standard analog voltmeters is not going to work. Only newer meters with high (approx 20MegOhm) impedance should be used to prevent loading the circuit which will draw down the voltage and skew the results. One side will likely have a signal. The other side will likely not. focus on the side with no signal. Sometimes, you can bridge pins 2 and 5 to see if you can get the second channel working again. If it does, then it confirms the amp is OK. Chances are, one of the coupling capacitors in the signal paths has gone south or you have a bad solder joint, fracture of a trace that may or may-not be visible.

 

[saxonman]

thanks my now best friend superduper!!! I'll check all that I'll get my mate over who is a bit more testing gear! I reckon it must be sumit like joints or such like!!! thanks again i'll keep ya posted

 

[docs]

I've got same problem on my Sharp 9797. I've indentified the amp chip as HA12026, would jumping pin 2 and 5 be the same on this amp chip or different pins ? I can't find a circuit diagram for it

 

[Superduper]

I've got same problem on my Sharp 9797. I've indentified the amp chip as HA12026, would jumping pin 2 and 5 be the same on this amp chip or different pins ? I can't find a circuit diagram for it

Is that a 16 pin Dual Inline Chip? I think that is a stereo decoder, and not an amp chip. I would NOT bridge anything on that chip or you may blow it out and replacements are very hard to find, if not impossible. Amp chips will almost always be fastened to an aluminum heatsink.

 

[docs]

Ouch, okay thanks for the info I'll take a look at the board again, don't want to hijack here just got the same issue is all.
I'm not sure this thing could be in any more of an awkward place

 

[Superduper]

Ouch, okay thanks for the info I'll take a look at the board again, don't want to hijack here just got the same issue is all.
I'm not sure this thing could be in any more of an awkward place

[ Image ]

Yep, that is the one. I think it's also the HA1392 amp. But you do need to be sure since different amps have different pin outs. If you bridge the inputs, you should only do it momentarily and only for the purpose to verify amp functionality. Normally, we use a circuit tracer.

 

[docs]

Thanks for the info. I have a dmm with 200m, 2m, 200k, 20k, 2k and 200 settings, how could I use this to do some grace testing please?

Incidentally, this 9797 is not an easy box to remove the amp board from as it is secured from both sides. I think in order to remove the amp board you have to remove everything from the back shell which is a nightmare.

 

[saxonman]

I have now given up on it!!!! tried everything now still no reward if anybody wants the box they can have it just pay the postage !!! another one bites the dust!!!

 

[docs]

I'm thinking the same thing saxo, I've got this in pieces at the moment but I think its fruitless.

Superduper, upon contacting 2 and 5 (2 being left and non working, and 5 being right and working) and having the balance offset to only come out of the left speaker I just get a hum or a buzz but no white noise from the radio. I tested continuity from the chip through to the jumper and onwards is fine. What further tests could I do to be 100% certain its the amp chip please ?

 

[Superduper]

Docs. First, the jumper needs to be super short because it will act as an antenna and pick up RF interference. Since this is a low level signal, everything will get amplified by the amplifier.

Secondly, the whole exercise here it to bring a known good audio signal to the input of the side that is not working. Hopefully, it will tell you if the amp is blown. If the amp is good and it's starved for an input signal, bringing the signal from the other side should accomplish that. With the signal being shared, reduced impedance could load down the other side so distortion and low output is not uncommon. Again, we are just trying to test the amps ability to amplify a signal. Keep in mind that the amp input signal at the pins is AFTER all signal processing. Do you see what you are doing wrong now?

By turning the balance knob ALL THE WAY to the bad side, you introduced another factor. If the issue is before the amp, say in the pre-amp, you just turned the signal to the possible dead side. So if the preamp is defective, and you turn the signal all the way to the bad side......... there is no way for the amp to amplify a dead signal. Try this again with the balance at neutral or at the good side and retry.

If all you got is a voltmeter, I'm not sure you have enough equipment to test and determine the problem. On the other hand, if you have a service diagram with V-R test point specs, then you CAN indeed test and determine whether the circuits are working as they should. Basically, as you traverse the circuit diagram, there will be voltage and resistance readings at various critical locations including almost all IC pins. If you have an audio signal generator, you can inject an audio signal at the amp to see if it will amplify the signal. If you have a signal tracer, you can test backwards from the amp through the circuit until you find a break in the signal. Anyhow, sorry but maybe someone else can think of a more simplified manner to test the amp for you.

As for the amp module being hard to extract -- that probably is not unusual. Most amps are in pretty obscure and hard to service locations. After all, amp failure is not that common of a malady. Also if you do need to remove the amp module, and you decide to do it yourself, always, always secure it properly to the heatsink with appropriate heatsink grease. Then solder it in last. That accomplishes 2 things. First, it always helps to have a little heatsinking to protect the chip. Second, once the chip is soldered in, it's almost impossible to fasten it down so it will sit flat against the heatsink. A GF-9797 is worth fixing. If you no longer want it, ship it to me.

 

[docs]

Many thanks for the information once again. I'll test it again at mid balance point ujst to see if I can get white noise from both and will let you know.