Aufarbeitung eines Hitachi HA 8700

2x 22 µF 25V ----> - 22 µF + + 22 µF -

Yes I knew it 2 capacitors in series on the + but I wanted to have your opinion anyway thank you for answering me I will keep you informed of the rest at the beginning of this week :-)

C'est mieux si tu attends. Il y a d'autres personnes sur le forum qui peuvent encore mieux t'aider.

The PROTON D1200 amp also I already repaired with its leaky diode on the VUMETER control which made the amp go into protection it was not easy to repair it

Ok thank you I will wait for other opinions from other people on the site, thank you.

I think the problem adjusting idle current is most likely in stage 3 (red).

Did you replace the 'fuse resistors' in stage 3?
R717L/R
R720L/R
R721L/R

They look like normal resistors but are aging fast, especially when under constant heat stress. Value will deviate up or down, both can happen. Value will also vary by temperature and humidity (!). In some cases, they measured correctly when desoldered (still warm and humidity has been driven out) but continued deviating when back in operation.

I always replace any fuse resistors I find.
After more than 40 years in a very hot MOSFET amplifier, this is a must.


These are fuse resistors I replaced in a Hitachi HA-6800 main amp section:




- Johannes

Hi yes I had to replace the R717L/R fuse resistors which had a very high value, I also changed 2 transmitter resistors which had a high value of 10 ohms instead of 2.7 ohms. the impossibility of setting the quiescent current occurs when I deactivate the main in switch but when I activate it I can set it to 300 mA, I check AND TEST the S701 L/R relay it works very well, the switch too

The capacitors that CarlM. told me to check its in the right value

Beim Hitachi HA-8700 werden Sicherungswiderstände (Fuse Resistors) ausgerechnet in Stufe 3 (rot) verwendet, wo der Ruhestrom eingestellt wird.
Art des Defekts: Fuse Resistors sind nicht immer komplett durchgebrannt, sondern verändern über die Jahre ihren Widerstandswert, teilweise nach oben und teilweise nach unten. Sie sehen aus wie normale Widerstände 1/4 Watt.

Im Schaltplan erkennt man diese Widerstände daran, dass sie schwarz gezeichnet sind:



R720L/R, R721L/R --- 100 Ohm 1/4 Watt --- Arbeitswiderstand 3. Stufe
R717L/R, R748L/R --- 100 & 120 Ohm 1/4 Watt --- "Long-Tail" Widerstand 3. Stufe
R737 --- 10 Ohm 1/4 Watt --- Trennung Signalmasse und Gehäusemasse


- Johannes

Hello I have already changed it, but I will check it anyway, when I have time, for the moment I have left it aside, otherwise I think the problem comes from the mosfet transistors 2sk134 and 2j49 its original parts are hard to find, any ideas for an equivalent?

I would recommend: Do not always trust the measurement value of certain old resistors.

To my knowledge, some fuse resistor types used to be implemented with organic material which may have drawn humidity causing deviation of value. But when desoldering and heating up, the resistor may temporarily measure ok, only to draw humidity again.

Electrolytic capacitor parameters also are manyfold, there is more than the capacitance and ESR that changes over the year. Leakage current and certain other parameters will cause it to fail or degrade in operation.

The impossibility of setting the quiescent current occurs when I deactivate the main in switch but when I activate it I can set it to 300 mA,

The main in switch could be the "direct coupling" switch?
If so, then be aware that it just bypasses a coupling capacitor which means that any DC from previous circuits may come through to the main amp input which has no coupling capacitor to my knowledge (although it has bipolar input transistors which normally require coupling caps).

- Johannes

Ok thank you for the advice, it is noted I changed 4 or 5 fuse resistors on the MAIN P.W.B 1 board the others were at the right value, I will change them anyway soon, concerning the adjustment of the quiescent current as I see it I said before I could adjust it only when the main in direct switch was on, but when it was turned off, the quiescent current was over 2 volts and the transistors were hot! regardless of whather the switch is in direct coupling or condenser coupling mode, but lately it was working fine then after 15 minutes then it went into protection, I don't know if it's a bad ground or a component that's broken lack.

With such elusive but reproducible problems, you may have bad solder joints ("kalte Lötstellen") across the PCBs.

- Johannes

This is an analysis of the signal path (left channel) to support troubleshooting the Hitachi HA-8700.




- Johannes

Hi thank you for this detailed diagram I will do it soon and I will keep you posted

Hallo alle zusammen!, kann mir jemand helfen? Mein Hitachi HA-8700 hat 210 Volt an der Gehäuse drauf!!! Weißt jemand was geht hier ab!
LG

Vorbereitung zur Diagnose:
alle! Steckverbinder zum Gerät abziehen und dann beschreiben, zwischen welchen Messpunkten du 210Volt feststellst. Kontrolle: Netztstecker einmal anders herum reinstecken und nochmal messen. Änderung?

Hi ! Dankeschön!, hat sich erledigt! Stecker gedreht und alles wieder in Ordnung!
Jetzt geht es ran an die Oxidierte Teile, Elektrolyte, Widerstände!

LG

OK, dann war die Spannung am Gehäuse entstanden durch parasitäre Effekte am Netzteil.
Bei Geräten, die keine Schutzerde angeschlossen haben, kann das durchaus mal passieren.
Die Spannungen können durchaus hoch sein, aber die fließenden Ströme sind zu gering, als dass man Schaden nehmen kann.

Hallo Broesel02, ich hoffe dir geht es gut!, ich habe eine Frage, es geht um Austausch von Polyesterkondensatoren von 0.22uF 250V auf 1.5uF 160V, auf der Platine sind 6 Stück Polyester 0.22uF 250V Kondensatoren, welche hast Du von die 6 Stück gemeint? Das würde mich sehr interessieren !

Danke

Mit freundlichen Grüßen

Du beziehst Dich wahrscheinlich auf Post #12.

Da ist aber eigentlich alles klar beschrieben. Es geht um die Folienkondensatoren, welche parallel zu den Puffer-Elkos sitzen.

Hallo Johannes,

ich denke es geht um #16:
http://www.hifi-foru...d=10403&postID=16#16

Dort sieht man in der Mitte zwei WIMA. Laut Service Manual S. 13 (von 30) befinden sich dort C708R und C708L mit je 33µF 16V (bipolare Elkos).
Irgendwie passt das also nicht so ganz. Zumindest scheint doch eine präzise Erklärung notwendig zu sein.

Carl

p.s.
Mir fällt gerade auf, dass die WIMA auf der Platine in #12 woanders sitzen ....