Why do public houses have the oldest systems? Maybe because the
SRD400 has been a reliable workhorse and publicans know how to be
careful with money! Bert Wetherill who runs the "Horse and Hounds"
was no stranger to thrift.
"It won't cost more than a tenner?" he told me, forcefully. "'Cause I
can get another at the car boot sale on Sunday. Only it'd be real
nice to have it back fer the match tonight. Plus, you don't want the
price of your pint to increase, do you?"
This last statement was made without a smile so I decided to get on
with the repair immediately!
The apparent symptom was low LNB voltage, switching between 10.6 and
13.4 volts on my meter. Of course I wasted half an hour messing with
the regulator circuit before realising there was a dry (corroded)
joint on the big 4700uF electrolytic. If I'd plugged the TV in I'd
have seen the hum bars
immediately - but I'm far too clever for that! I had to measure the
blooming voltages first and confuse myself by assuming I was
measuring smooth d.c.
I've known other competent repair men to be caught out by supposedly
"low secondary voltages" on power supplies. I always recommend using
an oscilloscope to check the power supply outputs because this will
instantly show if the voltage is regulated or has sawtooth spikes! On
day I'll take my own advice.
An additional problem was evident; although the channel number
changed as I pressed the "up" button, the actual picture didn't. It
alternated between just two programmes - one on vertical and one on
horizontal polarisation. Measurement indicated that the regulated 27
volt supply was only giving 3 volts. Replacement of the 2SK301 and
the AN431 cured this problem.
"The power went off and now the red light is flashing. I'm afraid to
turn it on in case it goes bang!"
Now, Jimmy is a timid person at the best of times. He's been a
gardener all his life and still prefers gas mantles to electric
lights, so his fear was understandable. However, all modern
Grundig-based receivers and "BT" receivers flash an LED when first
connected. It's there simply to remind you to set the internal clock
in case you decide to use the timer function for recording a
programme. Even the old SRD510 flashes its lights after a power cut
if the timer was set. It never ceases to amaze me how many dealers
phone me about this type of "fault". Am I the *only* person in the
world who reads the User Manual???
I stuck a piece of black tape over the offending LED and handed the
receiver back to Jimmy. He doesn't own a video recorder so he
wouldn't be setting the timer.
"Thanks, Mr Armstrong. I'll cut your grass, shall I?"
This unit arrived by carrier. I do contract work for a chain of
public houses and receivers often arrive unannounced! The decoder
message bars on screen were brilliant white without any text,
although the decoder worked perfectly. Replacing the graphics
generator, U27 (TCE-VCT01) had no effect. According to a helpful
young man at Pace, the message graphics are inserted onto the video
signal in U19 (4053). In this particular case, U19 pin 1 was
permanently high at 12 volts. The IC was faulty and replacement
effected a cure. Even the lads at Pace were surprised as this is not
a fault that had been reported previously. By the way; if you use
Pace's friendly help line and subsequently find the cause of your
fault, please take the trouble to fax them with details of the
original symptoms and your cure. This helps everyone.
This receiver appeared on the market as a direct rival to the MSS1000
from Pace. It has similar features in a slightly smaller box and the
price was somewhat lower. Recently, the price fell even further and
you could buy one for the price of a PRD800. As with anything, you
get what you pay for. The reliability, in my experience, is not too
bad but, if the receiver *does* fail, some spare parts are difficult
to obtain. For example, IC602 (labelled "AMS42577") controls the LNB
voltage and is "unavailable" from CPC as a spare part. Strange
because Pete Gurney tells me it's just a standard LM2574N switching
regulator!
But I digress. When Betty from the cake shop demonstrated her
receiver to me, it was clearly not well but nor was it a power supply
fault. The picture was dull and would occasionally go even more dull
or flash bright horizontal lines then give a blank screen. It looked
very much like the "Q105" symptom in later Pace PRD receivers so I
rubbed my hands together and thought "goody".
Two hours later I was less confident. The oscilloscope showed that
the baseband coming out of the tuner and entering TR5 was
"jittering". Both the dc level and the peak amplitude were varying.
Scraping my plastic toothbrush handle inside the tuner would correct
the fault for a few minutes but then it would return. I got out my
magnifying glass and resoldered a few joints as a token gesture but,
it seemed to me, that a semiconductor was failing.
I replaced the tuner but it made no difference. Then I noticed a tiny
connection on the circuit diagram which took the tuner baseband
output straight to... where?
Straight into the decoder, in fact, but the decoder circuit is not
shown in the service manual. So, the problem was definitely in the
decoder, which meant that the receiver was a write-off as I was not
prepared to spend any more time on it. Sometimes you just have to cut
your losses. Knowing when to stop is all part of running a business.
I'll find Betty a good second hand Pace receiver instead.
During the warranty period, the Grundig receivers apparently had an
incredibly low failure rate - but they are making up for that
now!
When Derek, a local installer, brought me a GRD150 and described the
fault as "horizontal line on picture" I had my suspicions that he was
describing a "hum bar" and plugged the mains cord in at arms
length.
A horrendous buzzing noise errupted from the power supply so I pulled
the plug, quickly!
I didn't need a magnifying glass to see that C201, the 47uF/400v
capacitor, was bulging.
"Wow" Derek breathed. "It was giving quite good pictures before it
cooled down. Just that line across and occasional scrambling. Is it
repairable?"
I assured him that it was and quickly replaced the offending
capacitor with one that I'd robbed from a "B.E.R." Minerva, earlier.
The result was perfect pictures and no more buzzing. Derek paid up
with good grace and drove off to fleece his customer.
This is a cheaper version of Grundig's GRD150 but uses a different
board from the "Omni" chassis used in the Minerva and Matsui
variants. Last week I saw my first one and I am still puzzled by the
fault. Both red and green LEDs lit permanently and the only response
to button presses was a slight dimming of the LEDs. On removing the
cover I could see that ALL the large electrolytics were bulging. This
smacked of power supply output voltages having gone too high so I
replaced all the faulty capacitors then applied power while
monitoring the 5 volt output. It was perfect but the symptoms
remained the same. I put the lid back on, quickly, in case I was
tempted to spend more time on it. The customer had set a 35 limit on
the cost so now was the time to give up! It seemed to me that some of
the ICs had been damaged by the overvoltage. If anyone has come
across this problem in a Grundig receiver, I'd be interested to know
the cause. There was no obvious fault on the primary side so why had
the output voltages risen so high that the electrolytics had been
damaged! (I suspect foul play).