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Hitachi CSP 680 - ex crustytv  

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EmleyMoor
(@emleymoor)
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This is proving to be a "one step forward, two steps back" kind of set, at the moment. I set up to measure one of the TR41 voltages, but could not, once again, get a raster or sound. Only about 200mV present. Checked fuses, seemingly OK, apart from possibly the two not on the circuit diagram, but they are harder to reach..

The fact that both my printer (due to consumables shortage) and laptop (due to CMOS battery failure) are out of action means I don't have access to the service manual in the same room as the set, complicating investigations, but both of these problems should be resolved soon.

When I have found suitable tools I will be getting the tuner out to investigate why it's partially seized. This will be done either while I'm waiting to deal with the printer and laptop or once I've got a raster again.

If I sort the tuner I would like to find a tuning ring, as this one is partially broken. If not, I'll be looking for another tuner ideally the same type (HU-548), but at a push the one from a CRP-145 (HU-518), as long as it has the knob with it. I have seen a few other alternative arrangements, and could go with those if necessary, but the tuner is one of the interesting things about these sets.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 29/08/2020 3:26 pm
kswhite
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Is this the model you had in your car phil

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Posted : 05/09/2020 4:34 pm
EmleyMoor
(@emleymoor)
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@kswhite Yes, of course.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 07/09/2020 7:41 pm
EmleyMoor
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Tests today showed, once again, no HT with plug K out of the deflection board. I have the power audio PCB out, and it seems to differ from the circuit diagram - VA903 is absent, solder is smooth, like it was never there.

I am planning to test the output from the transformer next, just to make sure the fault isn't there, before I dig any deeper into this board. All diodes I have found seem to be OK, fuses and resistors intact and those that are readable in circuit are right. Assuming all is well transformer side, I will try to identify how the circuit differs from the diagram. I will also try to check the two fuses that are not on the diagram, if transformer output tests show a problem.

If all this is sound, the power PCB will be the next suspect.

 

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 12/09/2020 12:20 pm
EmleyMoor
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All transformer voltages, and the chassis-mounted transistor and resistor in that part of the circuit, check out. The main capacitor, a 470µF/200V can, is outside the range of my meter, and could possibly be the cause, and to source a replacement at some point might be good, but I consider it less likely than other possibilities.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 12/09/2020 1:03 pm
EmleyMoor
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Instead of the cathode of CR39 connecting to the cathode of VA903, it connects to the cathode of VA901, via a wire link inserted as VA902. This seems to actually be how the board is marked. The vacant position for VA903 is between F903 and R906. Needing further tests, TR42 and all capacitors in the power part of the board.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 12/09/2020 1:40 pm
EmleyMoor
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Had time to investigate this a bit more.

TR42 (a 2SA673) may well have been OK but one leg fell off during testing.

R908 - meant to be 22K, 5% tolerance - is reading short - it's a large-ish resistor, RDIP by it according to the circuit diagram. Would a 2W carbon film type be OK as a replacement, or is something else needed? For typical resistors I normally use a 600mW metal film type, so if that is suitable so much the better.

C906 (330µF 16V) reads open circuit - maybe the smoke came from here. C907 gives an attempt to read but is too large in value to measure - I expected the same results from these.

C908 (10µF 160V) reads 18µF - no marked tolerance, and 80% over is not necessarily a problem, so will stick with it.

Ceramic capacitors are not presently suspected and all pass basic tests. Value too low for me to measure.

A BC327 or BC636 seem to be reasonable substitutes for 2SA673 - unless anyone here knows different I will go with the most economical.

 

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 12/11/2020 7:11 pm
irob2345
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The BC327 has a different pinout, the 2SA675 has collector as centre pin.

A BC640 has a matching pinout and is a "tougher" part with higher collector current and power dissipation ratings.

I recall from distant experience that it stands up to lightning hits much better too! In Sydney in the 70s and 80s a weekend electrical storm would guarantee a storm of phone calls for service on Monday morning!

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Posted : 13/11/2020 12:53 am
EmleyMoor
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OK - well, one of my suppliers has BC640 for the same price as BC327 and subject to an order multiple of only 5, so I have put that on my list. Once I get to the bottom of the resistor requirement, I will place an order.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 13/11/2020 10:48 am
EmleyMoor
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Oddly enough, due to a special Transatlantic shipment charge, it is cheaper to buy 50 BC640 from one supplier than to buy 5 from another. If I go for the cheaper deal and anyone needs any, I may well be able to supply.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 13/11/2020 10:02 pm
Katie Bush
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@emleymoor

Would that be the 'special arrangement' with the USPS? Which now levies a charge against all items of mail from China to the USA? The Chinese reciprocated by adding their own shipment charges to every item of mail they send out, regardless of where in the world it is destined, so because of the US Mail, we all now have to pay through the nose!

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Posted : 13/11/2020 11:01 pm
EmleyMoor
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@katie-bush I don't think so - it's because their entire stock of BC640s is on the other side. £15+ surcharge because of it. Other supplier can sell me ten times as many for about half what I'd pay in total.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 13/11/2020 11:32 pm
irob2345
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Suspect you are using the wrong supplier! 6k+ pcs in stock for next day delivery, 0.22p 5 pcs price.

https://uk.farnell.com/multicomp/bc640/transistor-pnp-to-92/dp/1574386?scope=partnumberlookahead&ost=BC640&searchref=searchlookahead&exaMfpn=true

 

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Posted : 14/11/2020 4:40 am
EmleyMoor
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@irob2345 Hmmm... oddly they didn't show me that particular line when I searched. Now I only need to solve the resistor issue.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 14/11/2020 11:08 am
EmleyMoor
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Parts on order. Postal issues may delay things a bit, but with luck I'll have a raster by Christmas.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 18/11/2020 3:37 pm
EmleyMoor
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Farnell order arriving today. Looks like early next week to actually fit the parts.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 20/11/2020 10:44 am
EmleyMoor
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OK, some progress... having replaced TR41 (with a BC640), R908 (with a metal oxide 2W resistor) and C906, the symptom is no longer "no raster", but "no video" - there is clearly a raster as deflection collapse is visible on switch-off. About 10.7V is present on the signal PCB at pin B1, and there are no shorts on connector A at all.

According to the flowchart, the next test is to apply a clicking noise to the base of TR1. Presumably, I need some way to generate this, or I could follow each side - assume excessive noise and check the VIF coaxial cable, the +B voltage of the tuner and the AGC voltage, but if all OK, assume possibly no noise and do the video amplification test using a 100nF capacitor between JA9 and P11. Horizontal streaks on this would point to an AGC issue in any case. I don't think I have a spare 100nF capacitor at present, but I can easily order one.

Any suggestions on how to apply the noise, or is that more likely to be a dead end? I am still interested in any case in finding a replacement tuner.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 25/11/2020 5:00 pm
EmleyMoor
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Tried a 10% each way adjustment of R911 - no significant change to HT which now reads about 112V. Only 10.3V on the 12V rail, it has been suggested by another friend of mine, may not be sufficient for the tuner. It's difficult to adjust R911 in a way that the voltages can be monitored, simply due to the way the boards are positioned, so will look towards causes of insufficient voltage.

"Yes, a bit of wet string may get you a good TV signal here on four channels, but you'll have to dry it out to get Channel 5!"

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Posted : 01/12/2020 4:38 pm
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